NEWS
It is amazing that India cannot let go if its meddling ways. With an employee ratio of over 200 per plane, Air India burns through cash at a frightening rate. Being state owned, it has too much of everything - except brains. The state creates jobs for pals and voters.So the Indian government has thrown flag carrier Air India a lifeline by offering a financial aid package on condition it undertakes a “massive cost reduction” program. The offer by the prime minister follows his meeting with the airline’s new chairman and managing director. With the election behind it, job cuts can be made at minimal political risk.Praful Patel, India’s aviation minister, said: “The government is fully committed to Air India to tide it over the present crisis”. However he added that as a condition Air India “must shape up, become leaner and trimmer, and also must put its best foot forward”. Patel said Air India, and the unions that represent its 31,000 workforce, must undertake radical cost-cutting and other financial improvements to qualify for the assistance.The airline has already said it was looking to cut $103m in staffing costs, about 17% of its total wage bill as it faces its worst liquidity crisis in its 75-year history. Good luck on this project -the reaction will be horrible. Remember when Jet cut its staff? There were protests that brought the state into the fray and the airline backed down.Debts are running at $4bn and last week Jadhav asked 150 top executives to voluntarily forgo salaries in July, and announced that June pay for staffers would be delayed by two weeks. In India this is a radical move - probably unprecedented.“This is an hour of crisis for all of us,” Jadhav said in an e-mail circulated to staff. “It is a fight for survival – the survival of our airline. I am looking for every single employee of our airline to rise to the challenge.” He has been listening carefully to WW don't you think?The government is reviewing the carrier’s order for more than 100 new aircraft, about half of which have yet to be delivered. So delivery delays can be expected. It also intends to shake up Air India’s board by appointing eight independent directors.After years of monopoly, Air India’s domestic market is coming under increasing pressure from leaner private airlines, reflected in its share in passenger traffic falling from 38% in 2004 to 15% this year. On an international level, markets are being eroded by intensifying competition from Gulf carriers, which are expanding aggressively into India. In other words, Emirates is eating their lunch. The Indian airlines are all under pressure.
Friday, July 31, 2009
Wednesday, July 29, 2009
ARIHANT
July 19, 2009 - India's first nuclear powered submarine will at best be a technology demonstrator and test bed for developing operational nuclear capabilities.Not much is known for sure about the submarine developed under the super secretive Advanced Technology Vessel (ATV) at this point of time, but the rough picture that emerges is of a 7,000 ton submarine powered by a 80MW PWR using enriched uranium. Current Indian submarine building expertise is based on the two German HDW 209 1500 submarines – INS Shalki and INS Shankul - that it built in the late eighties to early nineties.India does not have any submarine design experience let alone for a 7,000 ton class boat.It is likely Arihant is based on the Russian Charlie II submarine that India got to study when it leased INS Chakra for three years from 1988-91.Arihant likely incorporates a lot of advancements in propulsion, noise suppression, command and control, communication and sonar that the Russians learnt since they built the Charlie II subs, as well as what the Indians learnt while building the HDW boats.Unofficial illustrations of the boat show elements of Akula design like the towed sonar at the aft. However, Arihant is unlikely to be based on the Akula II or the more modern Graney class Russian subs, as reported in some sections of the press, since these subs use a twin hull design and are therefore considerably heavier.It is likely India has sourced components like propellers and shafts from Russia for the boat to minimize risks.The stress must have been to build a safe nuclear propulsion unit and adding ballistic missile launching capability to the submarine.Officially, India has consistently linked its ATV project to the need for a sea based credible nuclear deterrent. It can be assumed the ATV will carry nuclear capable missiles. It is not an SSN but an SSBN.The ATV is reportedly equipped with 4 launch tubes of 2.4m diameter each. Initially, each missile tube will likely accommodate 3 0.74m diameter K-15 Sagarika missile. Later the tubes could accommodate the 2.0m diameter Agni IIISL (The submarine launched version of the Agni V / Agni 3+) missiles with MIRV capability.Once Arihant's nuclear propulsion is proven the stress will shift to weapon testing.The Sagarika's limited range of 700km makes it inadequate even as a deterrent against Pakistan, let alone China.Hopefully, DRDO will be ready with the Agni IIISL within a year or two. It is likely that followup nuclear subs will accommodate more sections to carry at least 12 launch tubes.Followup Arihant class subs will represent a credible nuclear deterrent only when they are fielded with at least 12 Agni IIISL missiles capable of striking targets in most of China from within Indian coastal waters.It could well be another 10 years before that capability is reached.The ATV project appears to be well conceived and carefully calibrated. It has a good chance of succeeding despite past delay. Indian nuclear and missile technology is well developed and reasonably advanced, though DRDO's past record has not always been stellar.
Tuesday, July 21, 2009
CHEAP DIGITAL PRINTING
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Monday, July 20, 2009
PRINTING SERVICES
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Saturday, July 18, 2009
BLOOD HOUND
It will be faster than a speeding bullet: a pencil-shaped car powered by a jet engine and a rocket, roaring across a desert at 1,000mph.
If all goes to plan, Bloodhound SSC will break the land speed record by the largest ever margin, and, in 40 seconds of breathtaking thrust, inspire thousands of British school children to take science A levels.
Today, at the Science Museum, the project to build this car will be announced by Lord Drayson, the Science Minister, who in 2006 first proposed the project to the two men who between them have held the land speed record for 25 years.
Richard Noble, engineer, adventurer, and former wallpaper salesman, reached 633mph (1,019km/h) as he drove a turbojet-powered car named Thrust 2 across the Nevada desert. In 1997, he headed the project to build the Thrust SSC, driven by Andy Green, an RAF pilot, at 766mph.
Lord Drayson could understand the desire to drive fast. In his spare time, he raced his Aston Martin DBRS9 around Silverstone at up to 160mph.
“Andy Green was one of my personal heroes,” he said. “I wanted to meet him. At the time there was a rumour that Steve Fossett [the late American businessman and aviator] was building a car that would do 800mph. They said they could do 1,000mph.
“I thought, wow. What's it like to drive 1,000mph? How cool is that?” He told the two men that Britain's shortage of science graduates was so serious that the MoD was struggling to recruit enough engineers. (This month the Science Minister tried a different tack to encourage children to study maths and physics, by declaring his support for manned space missions.)
The task of driving the vehicle will fall to Wing Commander Green, 46, who will lie feet-first in the Bloodhound. As the car accelerates, from 0-1,050mph in 40 seconds, he will experience a force of 2.5G (2 times his bodyweight) and the blood will rush to his head.
As he decelerates, experiencing forces of up to 3G, the blood will drain to his feet and he could black out. He will practise for this pounding in a stunt aircraft, flying upside-down over the British countryside.
Since the car covers the length of four football pitches every second, he will require lightning reflexes. In 1997, as Thrust SSC passed through the sound barrier, it swung sideways and he locked the steering wheel at 90 degrees to recover.
Mr Noble said: “The car was probably a few thousandths of an inch out on one side and it blew 100ft left.”
No one is sure what problems await a car that travels 300mph faster.
A prototype jet engine, developed for the Eurofighter and bound for a museum, was donated to the project. This will take the car to 300mph, after which a “bespoke”' hybrid rocket designed by Daniel “Rocket Dan” Jubb, 24, from Manchester, who built his first rocket at the age of 5, and now supplies the US military, will boost the car up to 1,000mph.
If all goes to plan, Bloodhound SSC will break the land speed record by the largest ever margin, and, in 40 seconds of breathtaking thrust, inspire thousands of British school children to take science A levels.
Today, at the Science Museum, the project to build this car will be announced by Lord Drayson, the Science Minister, who in 2006 first proposed the project to the two men who between them have held the land speed record for 25 years.
Richard Noble, engineer, adventurer, and former wallpaper salesman, reached 633mph (1,019km/h) as he drove a turbojet-powered car named Thrust 2 across the Nevada desert. In 1997, he headed the project to build the Thrust SSC, driven by Andy Green, an RAF pilot, at 766mph.
Lord Drayson could understand the desire to drive fast. In his spare time, he raced his Aston Martin DBRS9 around Silverstone at up to 160mph.
“Andy Green was one of my personal heroes,” he said. “I wanted to meet him. At the time there was a rumour that Steve Fossett [the late American businessman and aviator] was building a car that would do 800mph. They said they could do 1,000mph.
“I thought, wow. What's it like to drive 1,000mph? How cool is that?” He told the two men that Britain's shortage of science graduates was so serious that the MoD was struggling to recruit enough engineers. (This month the Science Minister tried a different tack to encourage children to study maths and physics, by declaring his support for manned space missions.)
The task of driving the vehicle will fall to Wing Commander Green, 46, who will lie feet-first in the Bloodhound. As the car accelerates, from 0-1,050mph in 40 seconds, he will experience a force of 2.5G (2 times his bodyweight) and the blood will rush to his head.
As he decelerates, experiencing forces of up to 3G, the blood will drain to his feet and he could black out. He will practise for this pounding in a stunt aircraft, flying upside-down over the British countryside.
Since the car covers the length of four football pitches every second, he will require lightning reflexes. In 1997, as Thrust SSC passed through the sound barrier, it swung sideways and he locked the steering wheel at 90 degrees to recover.
Mr Noble said: “The car was probably a few thousandths of an inch out on one side and it blew 100ft left.”
No one is sure what problems await a car that travels 300mph faster.
A prototype jet engine, developed for the Eurofighter and bound for a museum, was donated to the project. This will take the car to 300mph, after which a “bespoke”' hybrid rocket designed by Daniel “Rocket Dan” Jubb, 24, from Manchester, who built his first rocket at the age of 5, and now supplies the US military, will boost the car up to 1,000mph.
Friday, July 17, 2009
ONLINE FUN GIFTS
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if you are in search of a place where you will found all the child accessories like nap mat,backpacks and etc then posylane.com is the right place for you.Posylane provides you a broad range of each and every item of your requirement within your budget.Lets take a look at the nap mat that they provides.Here,at posylane you will find a great collection of posylane nap mats.Their nap mats are made from high quality material of nylon and cotton with a ribbon trimmed, soft, fleecy blanket.They are also available in lot of attractive designs like Black with hot pink polka dot,cadet,pink pony border and many more.Now take a look at the kids backpacks that they provide.Here they provide you their huge collection of Stephen Joseph and Mint toddler backpacks, towel wrap .As all we know that Stephen Joseph and Mint Coddler backpack are world wide famous for their high quality design of their backpacks.In addition to this these backpacks had some additional features like they had comfortable shoulder straps,it has 100% cotton twill outer and etc.They also provide laundry bag in hwich used clothes can be done for laundry these also avialable at different colours and size.
Saturday, July 4, 2009
Interview With ISRO's Madhavan Nair
How do you assess cooperation of India and Russia in space?
ISRO has had a long standing and successful co-operation with the erstwhile USSR in Space with the active participation of USSR in setting up the Thumba Equatorial Rocket Launching Station (TERLS) in early Sixties, Joint meteorological studies using more than 1000 meteorological sounding rockets launched from Thumba supplied from USSR and launching for India's Aryabhata, Bhaskara-I and 2 and for IRS-1A, 1B and IRS-1C in addition to the Tracking support for several Indian satellites.
The most significant and successful co-operation with Russia is the development and supply of the cryogenic engines for the Geo-stationary Satellite Launch Vehicle (GSLV) on a commercial basis. A historical milestone in Indo-Russian Space Co-operation was achieved in 2001 when Indian Geo-synchronous Satellite Launch Vehicle successfully demonstrated its capability in its first development flight using the Russian developed Cryogenic Stage (CS) as its third stage.
India considers Russia as the long standing partner in the field of space from the inception stage of Indian Space Programme.
Is this cooperation diversified enough? What would you like to improve in it?
India cooperates with Russia in many fields of exploration and peaceful uses of outer space. It has many currently operational agreements in the fields of moon exploration, global navigation system, human space flight, spacecraft building for atmospheric studies, etc.
India would like to further strengthen the cooperation in the above fields and also would like to cooperate further in developing cheaper and reusable means of access to the space.
Can you disclose details of the proposed manned space missions in 2013 and 2015?
ISRO has prepared a Project Report for deploying a space capsule for carrying two humans to low earth orbit of about 275 km for a duration of about a week which is being processed for approval. Once approved, formal approval from the Government is awaited. The first mission is likely during 2015.
When the approval of the manned space mission is expected?
Chandrayan I has been India's great success. How does it do on the orbit - any signs of water or Helium-3 so far? What main achievements it has made so far?
Chandrayaan has successfully completed 9 months of satisfactory operation in orbit and has sent vast amount of data on unique features of lunar surface. Presently the data is being analysed by scientific community from India and abroad. As of now, we have not found any signs of water or Helium-3.
How is work progressing on Chandrayan II, what is project status?
We have an operational agreement for a joint unmanned lunar landing mission and the definition of the mission has been completed. The Chandrayaan-2 mission will have an orbital flight vehicle constituting an Orbiter Craft (OC) and Lunar Craft (LC) that will carry a soft landing system up to Lunar Transfer Trajectory (LTT).
The target location for the Lander-rover will be identified using data from Chandrayaan-1 instruments. ISRO is responsible for developing the Orbiter while Russia is responsible for developing the Lander and Rover. Additional scientific payloads will be acquired from international scientific community through announcement of opportunity.
The mission is targeted for 2011-12.
When the launch of YouthSat satellite will take place? Can we expect YouthSat-2 any time soon?To encourage the participation of students community in spacecraft building and data utilization, a satellite project involving students from Indian and Russian Universities has been conceived under the Mini Satellite Programme of ISRO.
Accordingly a satellite named as Youthsat with 2 scientific payloads from ISRO and one from Moscow State University are planned to be flown to study the phenomenon of solar flare and ionospherical studies. YOUTHSAT is planned to be launched along with Resourcesat-2 in the third quarter of 2009.
Of course, we can expect similar projects coming up in future such missions are highly beneficial in motivating the younger generation.
Has the slowdown in the economy cast any effect on Indian space program? In what field?
Indian space programme is oriented towards research and development in spacescience
and technology. These programmes are also must for development of society and government fully supports such activities.
What is the status of Mark III rocket project?
Activities related to GSLV-Mark III capable of putting a 4 tonne satellite into GTO is progressing satisfactorily. Various facilities needed for development of the vehicle have been commissioned. The first launch is targeted for 2010-11.
India is a serious player on imaging market. How big share India can take of the global market in this regard, what are targets? When 'Bhuvan' project will be complete and ready? Will it be free like Google Earth but much better? What is status?
The data from Indian Remote Sensing satellites are received at 24 stations across the globe. Our share of remote sensing satellite data is about 18 to 20 percent of the global market. Bhuvan is a web based portal service providing access to 2 dimensional and 3 dimensional data from IRS satellites and geo-spatial information generated from them. The Bhuvan is currently under test and evaluation.
What is status of Mars mission project? How far ISRO ambitions are reaching?Mars mission is presently under study. We are awaiting interesting scientific proposals from the scientific community. Only after reviewing the scientific experiments/proposals project proposal will be finalised.
How do you assess cooperation of India and Russia in space?
ISRO has had a long standing and successful co-operation with the erstwhile USSR in Space with the active participation of USSR in setting up the Thumba Equatorial Rocket Launching Station (TERLS) in early Sixties, Joint meteorological studies using more than 1000 meteorological sounding rockets launched from Thumba supplied from USSR and launching for India's Aryabhata, Bhaskara-I and 2 and for IRS-1A, 1B and IRS-1C in addition to the Tracking support for several Indian satellites.
The most significant and successful co-operation with Russia is the development and supply of the cryogenic engines for the Geo-stationary Satellite Launch Vehicle (GSLV) on a commercial basis. A historical milestone in Indo-Russian Space Co-operation was achieved in 2001 when Indian Geo-synchronous Satellite Launch Vehicle successfully demonstrated its capability in its first development flight using the Russian developed Cryogenic Stage (CS) as its third stage.
India considers Russia as the long standing partner in the field of space from the inception stage of Indian Space Programme.
Is this cooperation diversified enough? What would you like to improve in it?
India cooperates with Russia in many fields of exploration and peaceful uses of outer space. It has many currently operational agreements in the fields of moon exploration, global navigation system, human space flight, spacecraft building for atmospheric studies, etc.
India would like to further strengthen the cooperation in the above fields and also would like to cooperate further in developing cheaper and reusable means of access to the space.
Can you disclose details of the proposed manned space missions in 2013 and 2015?
ISRO has prepared a Project Report for deploying a space capsule for carrying two humans to low earth orbit of about 275 km for a duration of about a week which is being processed for approval. Once approved, formal approval from the Government is awaited. The first mission is likely during 2015.
When the approval of the manned space mission is expected?
Chandrayan I has been India's great success. How does it do on the orbit - any signs of water or Helium-3 so far? What main achievements it has made so far?
Chandrayaan has successfully completed 9 months of satisfactory operation in orbit and has sent vast amount of data on unique features of lunar surface. Presently the data is being analysed by scientific community from India and abroad. As of now, we have not found any signs of water or Helium-3.
How is work progressing on Chandrayan II, what is project status?
We have an operational agreement for a joint unmanned lunar landing mission and the definition of the mission has been completed. The Chandrayaan-2 mission will have an orbital flight vehicle constituting an Orbiter Craft (OC) and Lunar Craft (LC) that will carry a soft landing system up to Lunar Transfer Trajectory (LTT).
The target location for the Lander-rover will be identified using data from Chandrayaan-1 instruments. ISRO is responsible for developing the Orbiter while Russia is responsible for developing the Lander and Rover. Additional scientific payloads will be acquired from international scientific community through announcement of opportunity.
The mission is targeted for 2011-12.
When the launch of YouthSat satellite will take place? Can we expect YouthSat-2 any time soon?To encourage the participation of students community in spacecraft building and data utilization, a satellite project involving students from Indian and Russian Universities has been conceived under the Mini Satellite Programme of ISRO.
Accordingly a satellite named as Youthsat with 2 scientific payloads from ISRO and one from Moscow State University are planned to be flown to study the phenomenon of solar flare and ionospherical studies. YOUTHSAT is planned to be launched along with Resourcesat-2 in the third quarter of 2009.
Of course, we can expect similar projects coming up in future such missions are highly beneficial in motivating the younger generation.
Has the slowdown in the economy cast any effect on Indian space program? In what field?
Indian space programme is oriented towards research and development in spacescience
and technology. These programmes are also must for development of society and government fully supports such activities.
What is the status of Mark III rocket project?
Activities related to GSLV-Mark III capable of putting a 4 tonne satellite into GTO is progressing satisfactorily. Various facilities needed for development of the vehicle have been commissioned. The first launch is targeted for 2010-11.
India is a serious player on imaging market. How big share India can take of the global market in this regard, what are targets? When 'Bhuvan' project will be complete and ready? Will it be free like Google Earth but much better? What is status?
The data from Indian Remote Sensing satellites are received at 24 stations across the globe. Our share of remote sensing satellite data is about 18 to 20 percent of the global market. Bhuvan is a web based portal service providing access to 2 dimensional and 3 dimensional data from IRS satellites and geo-spatial information generated from them. The Bhuvan is currently under test and evaluation.
What is status of Mars mission project? How far ISRO ambitions are reaching?Mars mission is presently under study. We are awaiting interesting scientific proposals from the scientific community. Only after reviewing the scientific experiments/proposals project proposal will be finalised.
Thursday, July 2, 2009
nAvigAtiOn And PlaNNinG
Overview and basic terminology
A flight planning system may need to produce more than one flight plan for a single flight:
Summary plan for Air Traffic Control (in FAA and/or ICAO format).
Summary plan for direct download into an onboard flight management system.
Detailed plan for use by pilots.
The basic purpose of a flight planning system is to calculate how much trip fuel is needed in the air navigation process by an aircraft when flying from an origin airport to a destination airport. Aircraft must also carry some reserve fuel to allow for unforeseen circumstances, such as an inaccurate weather forecast, or Air Traffic Control requiring an aircraft to fly at a lower height than optimum due to congestion, or some last-minute passengers whose weight was not allowed for when the flight plan was prepared. The way in which reserve fuel is determined varies greatly, depending on airline and locality. The most common methods are:
USA domestic operations conducted under Instrument Flight Rules: enough fuel to fly to the first point of intended landing, then fly to an alternate airport (if weather conditions require an alternate airport), then for 45 minutes thereafter at normal cruising speed.
percentage of time: typically 10%, i.e. a 10 hour flight needs enough reserve to fly for another hour.
percentage of fuel: typically 5%, i.e. a flight requiring 20,000 kg of fuel needs a reserve of 1,000 kg.
Except for some USA domestic flights, a flight plan normally has an alternate airport as well as a destination airport. The alternate airport is for use in case the destination airport becomes unusable while the flight is in progress (due to weather conditions, a strike, a crash, terrorist activity, etc.). This means that when the aircraft gets near the destination airport, it must still have enough alternate fuel and alternate reserve available to fly on from there to the alternate airport. Since the aircraft is not expected at the alternate airport, it must also have enough holding fuel to circle for a while (typically 30 minutes) near the alternate airport while a landing slot is found. United States domestic flights are not required to have sufficient fuel to proceed to an alternate airport when the weather at the destination is forecast to be better than 2,000-foot (610 m) ceilings and 3 statute miles of visibility; however, the 45-minute reserve at normal cruising speed still applies.
It is often considered a good idea to have the alternate some distance away from the destination (e.g. 100 miles) so that bad weather is unlikely to close both the destination and the alternate; distances up to 600 miles (970 km) are not unknown. In some cases the destination airport may be so remote (e.g. Pacific island) that there is no feasible alternate airport; in such a situation an airline may instead include enough fuel to circle for 2 hours near the destination, in the hope that the airport will become available again within that time.
There is often more than one possible route between two airports. Subject to safety requirements, commercial airlines generally wish to minimise costs by appropriate choice of route, speed, and height.
Various names are given to weights associated with an aircraft and/or the total weight of the aircraft at various stages.
Payload is the total weight of the passengers, their luggage, and any cargo. A commercial airline makes its money by charging to carry payload.
Operating weight empty is the basic weight of the aircraft when ready for operation, including crew but excluding any payload or fuel.
Zero fuel weight is the sum of operating weight empty and payload, i.e. the laden weight of an aircraft, excluding any fuel.
Ramp weight is the weight of an aircraft at the terminal building when ready for departure. This includes the zero fuel weight and all required fuel.
Brake release weight is the weight of an aircraft at the start of a runway, just prior to take-off. This is the ramp weight minus any fuel used for taxiing. Major airports may have runways which are about two miles (3 km) long, so merely taxiing from the terminal to the end of the runway might consume up to a ton of fuel. After taxiing the pilot lines up the aircraft with the runway and puts the brakes on. On receiving take-off clearance, the pilot throttles up the engines and releases the brakes to start accelerating along the runway in preparation for taking off.
Take off weight is the weight of an aircraft as it takes off part way along a runway. Few flight planning systems calculate the actual take-off weight; instead, the fuel used for taking off is counted as part of the fuel used for climbing up to the normal cruise height.
Landing weight is the weight of an aircraft as it lands at the destination. This is the brake release weight minus the trip fuel burnt. It includes the zero fuel weight and all alternate, holding, and reserve fuel.
When twin-engine aircraft are flying across oceans, deserts, etc. the route must be carefully planned so that the aircraft can always reach an airport, even if one engine fails. The applicable rules are known as ETOPS (Extended-range Twin-engine Operational Performance Standards). The general reliability of the particular type of aircraft and its engines and the maintenance quality of the airline are taken into account when specifying for how long such an aircraft may fly with only one engine operating (typically from 1 to 3 hours).
Flight planning systems must be able to cope with aircraft flying below sea level, which will often result in a negative altitude. For example Amsterdam Schiphol Airport has an elevation of -3 metres. The surface of the Dead Sea is 417 metres below sea level, so low level flights in this vicinity can be well below sea level.[2]
Units of measurement
Flight plans use an unusual mixture of metric and non-metric units of measurement. The particular units used may vary by aircraft, by airline, and by location (e.g. different height units may be used at different points during a single flight).
Distance units
Distances are always measured in nautical miles, as calculated at a height of 32,000 feet (9,800 m), with due allowance for the fact that the earth is an oblate spheroid rather than a perfect sphere.
Aviation charts always show distances as rounded to the nearest nautical mile, and these are the distances which are shown on a flight plan. Flight planning systems may need to use the unrounded values in their internal calculations for improved accuracy.
Fuel units
There are a variety of ways in which fuel can be measured, depending mainly on the gauges fitted to a particular aircraft. The most common unit of fuel measurement is kilograms; other possible measures include pounds, UK gallons, US gallons, and litres. When fuel is measured by weight the specific gravity of the fuel must be taken into account when checking tank capacity. Specific gravity may vary depending on the location and the supplier.
There has been at least one occasion on which an aircraft ran out of fuel due to an error in converting between kilograms and pounds. In this particular case the flight crew managed to glide to a nearby airport and land safely.
Many airlines request that fuel quantities be rounded to a multiple of 10 or 100 units. This can cause some interesting rounding problems, especially when subtotals are involved. Safety issues must also be considered when deciding whether to round up or down.
Height units
The actual height of an aircraft is based on use of a pressure altimeter - see flight level for more detail. The heights quoted here are thus the nominal heights under standard conditions of temperature and pressure rather than the actual heights. All aircraft operating on flight levels calibrate altimeters to the same standard setting regardless of the actual sea level pressure, so little risk of collision arises.
In most areas, height is reported as a multiple of 100 feet (30 m), i.e. A025 is nominally 2,500 feet (760 m). When cruising at higher altitudes aircraft adopt Flight Levels (FL). Flight Levels are altitudes corrected and calibrated against the International Standard Atmosphere (ISA). These are expressed as a three figure group e.g. FL320 is 32,000 Feet (ISA).
In most areas vertical separation between aircraft is either 1000 or 2,000 feet (610 m).
In China and some neighbouring areas, height is handled using metres. Vertical separation between aircraft is either 300 metres or 600 metres (about 1.6% less than 1000 or 2000 feet).
Up until 1999, the vertical separation between aircraft flying on the same airway was 2,000 feet (610 m). Since then there has been a phased introduction around the world of Reduced Vertical Separation Minimum (RVSM). This cuts the vertical separation to 1,000 feet (300 m) between about 29,000 feet (8,800 m) and 41,000 feet (the exact limits vary slightly from place to place). Since most jet aircraft operate between these heights, this measure effectively doubles the available airway capacity. To use RVSM, aircraft must have certified altimeters, and autopilots must meet more accurate standards.
Speed units
Aircraft cruising at lower altitudes normally use knots as the primary speed unit, while aircraft that are higher (above Mach Crossover Altitude) normally use Mach number as the primary speed unit, though flight plans often include the equivalent speed in knots as well (the conversion includes allowance for temperature and height). In a flight plan, a Mach number of "Point 82" means that the aircraft is travelling at 0.820 (82%) the speed of sound.
The widespread use of Global Positioning Systems (GPS) allows cockpit navigation systems to provide air speed and ground speed more or less directly.
Another method of obtaining speed and position is the Inertial Navigation System (INS), which keeps track a vehicle's acceleration using gyroscopes and linear accelerometers; this information can then be integrated in time to obtain speed and position, as long as the INS was properly calibrated before departure. INS has been present in civil aviation for a few decades and is mostly used in medium to large aircraft as the system is fairly complex.
If neither GPS or INS are used, the following steps are required to obtain speed information:
An airspeed indicator is used to measure indicated airspeed (IAS) in knots.
IAS is converted to calibrated airspeed (CAS) using an aircraft-specific correction table.
CAS is converted to equivalent airspeed (EAS) by allowing for compressibility effects.
EAS is converted to true airspeed (TAS) by allowing for density altitude, i.e. height and temperature.
TAS is converted to ground speed by allowing for any head or tail wind.
Weight units
The weight of an aircraft is most commonly measured in kilograms, but may sometimes be measured in pounds, especially if the fuel gauges are calibrated in pounds or gallons. Many airlines request that weights be rounded to a multiple of 10 or 100 units. Great care is needed when rounding to ensure that physical constraints are not exceeded.
When chatting informally about a flight plan, approximate weights of fuel and/or aircraft may be referred to in tons. This 'ton' is generally either a metric tonne or a UK long ton, which differ by less than 2%, or a short ton, which is about 10% less.
Describing a route
A route is a description of the path followed by an aircraft when flying between airports. Most commercial flights will travel from one airport to another, but private aircraft, commercial sightseeing tours, and military aircraft may often do a circular or out-and-back trip and land at the same airport from which they took off.
Components
Aircraft fly on airways under the direction of Air Traffic Control. An airway has no physical existence, but can be thought of as a 'motorway' in the sky. On an ordinary motorway, cars use different lanes to avoid collisions, while on an airway, aircraft fly at different flight levels to avoid collisions. One can often see planes passing directly above or below one's own. Charts showing airways are published and are usually updated once a month coinciding with the AIRAC cycle. AIRAC (Aeronautical Information Regulation and Control) occurs every fourth Thursday when every country publishes their changes, which are usually to airways.
Each airway starts and finishes at a waypoint, and may contain some intermediate waypoints as well. Waypoints use five letters, e.g., PILOX, and those that double as non-directional beacons use three or two: TNN, WK. Airways may cross or join at a waypoint, so an aircraft can change from one airway to another at such points. A complete route between airports often uses several airways. Where there is no suitable airway between two waypoints, and using airways would result in a somewhat roundabout route, air traffic control may allow a direct waypoint to waypoint routing which does not use an airway (often abbreviated in flight plans as 'DCT').
Most waypoints are classified as compulsory reporting points, i.e. the pilot (or the onboard flight management system) reports the aircraft position to air traffic control as the aircraft passes a waypoint. There are two main types of waypoints:
A named waypoint appears on aviation charts with a known latitude and longitude. Such waypoints over land often have an associated radio beacon so that pilots can more easily check where they are. Useful named waypoints are always on one or more airways.
A geographic waypoint is a temporary position used in a flight plan, usually in an area where there are no named waypoints, e.g. most oceans in the southern hemisphere. Air traffic control require that geographic waypoints have latitudes and longitudes which are a whole number of degrees.
Note that airways do not connect directly to airports.
After take-off an aircraft follows a Departure Procedure (SID or Standard Instrument Departure) which defines a pathway from an airport runway to a waypoint on an airway, so that an aircraft can join the airway system in a controlled manner. Most of the climb portion of a flight will take place on the SID.
Before landing an aircraft follows an Arrival Procedure (STAR or Standard Terminal Arrival Route) which defines a pathway from a waypoint on an airway to an airport runway, so that aircraft can leave the airway system in a controlled manner. Much of the descent portion of a flight will take place on a STAR.
Airline routes between Los Angeles and Tokyo approximately follow a direct great circle route (top), but use the jet stream (bottom) when heading eastwardsSpecial routes known as ocean tracks are used across some oceans, mainly in the northern hemisphere to increase traffic capacity on busy routes. Unlike ordinary airways which change infrequently, ocean tracks change twice a day, so as to take advantage of any favourable winds. Flights going with the jet stream may be an hour shorter than those going against it. Ocean tracks often start and finish perhaps a hundred miles offshore at named waypoints to which a number of airways connect. Tracks across northern oceans are suitable for east-west or west-east flights, which constitute the bulk of the traffic in these areas.
Complete routes
There are a number of ways of constructing a route. All scenarios using airways use SIDs and STARs for departure and arrival. Any mention of airways might include a very small number of 'direct' segments to allow for situations when there are no convenient airway junctions. In some cases political considerations may influence the choice of route (e.g. aircraft from one country cannot overfly some other country).
Airway(s) from origin to destination. Most flights over land fall into this category.
Airway(s) from origin to an ocean edge, then an ocean track, then airway(s) from ocean edge to destination. Most flights over northern oceans fall into this category.
Airway(s) from origin to an ocean edge, then a free-flight area across an ocean, then airway(s) from ocean edge to destination. Most flights over southern oceans fall into this category
Free-flight area from origin to destination. This is a relatively uncommon situation for commercial flights.
Even in a free-flight area, air traffic control still requires a position report about once an hour. Flight planning systems organise this by inserting geographic waypoints at suitable intervals. For a jet aircraft these intervals are 10 degrees of longitude for east-bound or west-bound flights and 5 degrees of latitude for north-bound or south-bound flights. In free-flight areas commercial aircraft normally follow a least-time-track so as to use as little time and fuel as possible. A great circle route would have the shortest ground distance, but is unlikely to have the shortest air-distance, due to the effect of head or tail winds. A flight planning system may have to do quite a lot of analysis in order to determine a good free-flight route.
Fuel calculation
Calculation of fuel requirements (especially trip fuel and reserve fuel) is the most safety-critical aspect of flight planning. This calculation is somewhat complicated:
Rate of fuel burn depends on ambient temperature, aircraft speed, and aircraft altitude, none of which are entirely predictable.
Rate of fuel burn also depends on airplane weight, which changes as fuel is burned.
Some iteration is generally required due to the need to calculate interdependent values, e.g. reserve fuel is often calculated as a percentage of trip fuel, but trip fuel can't be calculated until the total weight of the aircraft is known, including the weight of the reserve fuel!
Considerations
Fuel calculation must take many factors into account.
Weather forecasts
The air temperature affects the efficiency/fuel consumption of aircraft engines. The wind may provide a head or tail wind component which in turn will increase or decrease the fuel consumption by increasing or decreasing the air distance to be flown.
By agreement with the International Civil Aviation Organization, there are two national weather centres (in U.S.A. and U.K.) which provide worldwide weather forecasts for civil aviation in a format known as GRIB weather. These forecasts are generally issued every 6 hours, and cover the next 36 hours at intervals of 6 hours. Each 6-hour forecast covers the whole world using gridpoints located at intervals of 75 miles (121 km) or less. At each grid point the weather (wind speed, wind direction, air temperature) is supplied at 9 different heights ranging from about 4,500 feet (1,400 m) up to about 55,000 feet (17,000 m).
Aircraft seldom fly exactly through weather gridpoints or at the exact heights at which weather predictions are available, so some form of horizontal and vertical interpolation is generally needed. For 75-mile (121 km) intervals, linear interpolation is satisfactory. GRIB format superseded the earlier ADF format in 1998/9. The ADF format used 300-mile (480 km) intervals; this interval was large enough to miss some storms completely, so calculations using ADF predicted weather were often not as accurate as those which can be produced using GRIB weather.
Routes and flight levels
The particular route to be flown determines the ground distance to cover, while winds on that route determine the air distance to be flown. Each inter-waypoint portion of an airway may have different rules as to which flight levels may be used. Total aircraft weight at any point determines the highest flight level which can be used. Cruising at a higher flight level generally requires less fuel than at a lower flight level, but extra climb fuel may be needed to get up to the higher flight level (it is this extra climb fuel and the different fuel consumption rate which cause discontinuities).
Physical constraints
Almost all the weights mentioned above in 'Overview and basic terminology' may be subject to minimum and/or maximum values. Due to stress on the wheels and undercarriage when landing, the maximum safe landing weight may be considerably less than the maximum safe brake-release weight. In such cases, an aircraft which encounters some emergency and has to land straight after taking off may have to circle for a while to use up fuel, or else jettison some fuel, or else land immediately and risk having the undercarriage collapse.
Also, the fuel tanks have some maximum capacity. On some occasions, commercial flight planning systems find that an impossible flight plan has been requested. The aircraft can't possibly reach the intended destination, even with no cargo or passengers, since the fuel tanks are just not big enough to hold the amount of fuel needed; it would appear that some airlines are over-optimistic at times, perhaps hoping for a (very) strong tailwind.
Fuel consumption rate
The rate of fuel consumption for aircraft engines depends on: air temperature, height as measured by air pressure, aircraft weight, aircraft speed relative to the air, and any increased consumption as compared with brand-new engines due to engine age and/or poor maintenance (an airline can estimate this degradation by comparing actual and predicted fuel burn). Note that a large aircraft such as a jumbo jet may burn up to 80 tons of fuel on a 10 hour flight, so there is a substantial weight change during the flight.
Calculation
The weight of fuel forms a significant part of the total weight of an aircraft, so any fuel calculation must take into account the weight of any fuel not yet burnt. Instead of trying to predict fuel load not yet burnt, a flight planning system can handle this situation by working backwards along the route, starting at the alternate, going back to the destination, and then going back waypoint by waypoint to the origin.
A more detailed outline of the calculation follows. Several (possibly many) iterations are usually required, either to calculate interdependent values such as reserve fuel and trip fuel, or to cope with situations where some physical constraint has been exceeded. In the latter case it is usually necessary to reduce the payload (less cargo or less passengers). Some flight planning systems use elaborate systems of approximate equations to simultaneously estimate all the changes required; this can greatly reduce the number of iterations needed.
If an aircraft lands at the alternate, in the worst case it can be assumed to have no fuel left (in practice there will be enough reserve fuel left to at least taxi off the runway). Hence a flight planning system can calculate alternate holding fuel on the basis that the final aircraft weight is just the zero fuel weight. Since the aircraft is circling while holding there is no need to take wind into account for this or any other holding calculation.
For the flight from destination to alternate, a flight planning system can calculate alternate trip fuel and alternate reserve fuel on the basis that the aircraft weight on reaching the alternate is zero fuel weight plus alternate holding.
A flight planning system can then calculate any destination holding on the basis that the final aircraft weight is zero fuel weight plus alternate holding plus alternate fuel plus alternate reserve.
For the flight from origin to destination, the weight on arrival at the destination can be taken as zero fuel weight plus alternate holding plus alternate fuel plus alternate reserve plus destination holding. A flight planning system can then work back along the route, calculating the trip fuel and reserve fuel one waypoint at a time, with the fuel required for each inter-waypoint segment forming part of the aircraft weight for the next segment to be calculated.
At each stage and/or at the end of the calculation, a flight planning system must carry out checks to ensure that physical constraints (e.g. maximum tank capacity) have not been exceeded. Problems mean that either the aircraft weight must be reduced in some fashion, or else the calculation must be abandoned.
An alternative approach to fuel calculation is to calculate alternate and holding fuel as above, and obtain some estimate of the total trip fuel requirement, either based on previous experience with that route and aircraft type, or by using some approximate formula; neither method can take much account of weather. Calculation can then proceed forwards along the route waypoint by waypoint. On reaching the destination, the actual trip fuel can be compared with the estimated trip fuel, a better estimate made, and the calculation repeated as required.
Cost reduction
Commercial airlines generally wish to keep the cost of a flight as low as possible. There are three main factors which contribute to the cost:
amount of fuel needed (to complicate matters, fuel may cost different amounts at different airports),
actual flying time affects depreciation charges and maintenance schedules etc.,
overflight charges are levied by each country the aircraft flies over (notionally to cover air traffic control costs).
Different airlines have different views as to what constitutes a least cost flight:
Least cost based only on time.
Least cost based only on fuel.
Least cost based on a balance between fuel and time.
Least cost based on fuel costs and time costs and overflight charges.
[edit] Basic improvements
For any given route, a flight planning system can reduce cost by finding the most economical speed at any given height, and by finding the best height(s) to use based on the predicted weather. Such local optimisation can be done on a waypoint by waypoint basis.
Commercial airlines do not want an aircraft to change height too often (among other things, it may make it more difficult for the cabin crew to serve meals), so they often specify some minimum time between optimisation-related flight level changes. To cope with such requirements a flight planning system must be capable of non-local height optimisation by simultaneously taking a number of waypoints into account, along with the fuel costs for any short climbs that may be required.
When there is more than one possible route between the origin and destination airports, the task facing a flight planning system becomes more complicated, since it must now consider many routes in order to find the best available route. Many situations have tens or even hundreds of possible routes, and there are some situations with over 25,000 possible routes (e.g. London to New York with free-flight below the track system). The amount of calculation required to produce an accurate flight plan is so substantial that it is not feasible to examine every possible route in detail. A flight planning system must have some fast way of cutting the number of possibilities down to a manageable number before undertaking a detailed analysis.
Reserve reduction
From an accountant's viewpoint, the provision of reserve fuel costs money (the fuel needed to carry the hopefully unused reserve fuel). Techniques known variously as reclear or redispatch or decision point procedure have been developed, which can greatly reduce the amount of reserve fuel needed while still maintaining all required safety standards. These techniques are based on having some specified intermediate airport to which the flight can divert if necessary;[1] in practice such diversions are rare. The use of such techniques can save several tons of fuel on long flights, or it can increase the payload carried by a similar amount.[3]
A reclear flight plan has two destinations. The final destination airport is where the flight is really going to, while the initial destination airport is where the flight will divert to if more fuel is used than expected during the early part of the flight. The waypoint at which the decision is made as to which destination to go to is called the reclear fix or decision point. On reaching this waypoint, the flight crew make a comparison between actual and predicted fuel burn and check how much reserve fuel is available. If there is sufficient reserve fuel then the flight can continue to the final destination airport, otherwise the aircraft must divert to the initial destination airport.
The initial destination is positioned so that less reserve fuel is needed for a flight from the origin to the initial destination than for a flight from the origin to the final destination. Under normal circumstances little if any of the reserve fuel is actually used, so when the aircraft reaches the reclear fix it still has (almost) all the original reserve fuel on board, which is enough to cover the flight from the reclear fix to the final destination.
The idea of reclear flights was first published in 'Boeing Airliner' (1977) by Boeing engineers David Arthur and Gary Rose.[3] The original paper contains a lot of magic numbers relating to the optimum position of the reclear fix, etc. These numbers apply only to the specific type of aircraft considered, for a specific reserve percentage, and take no account of the effect of weather. The fuel savings due to reclear depend on three factors:
The maximum achievable saving depends on the position of the reclear fix. This position can't be determined theoretically since there are no exact equations for trip fuel and reserve fuel. Even if it could be determined exactly, there may not be a waypoint at the right place anyway.
One factor identified by Arthur and Rose which helps achieve the maximum possible saving is to have an initial destination which is positioned so that descent to the initial destination starts immediately after the reclear fix. This is beneficial because it minimises the reserve fuel needed between reclear fix and initial destination, and hence maximises the amount of reserve fuel available at the reclear fix.
The other factor which is also helpful depends on the positioning of the initial alternate airport.
Filing Suboptimal Plans
Despite all the effort taken to optimise flight plans there are certain circumstances where it is advantageous to file suboptimal plans. In busy airspace with a number of competing aircraft, the optimum routes and preferred altitudes may well be oversubscribed. This problem can be made worse by busy periods, for example where everyone wants to arrive at an airport as soon as it opens for the day. If all the aircraft file an optimal flight plan then to avoid overloading, air traffic control may refuse permission for some of the flight plans or delay the allocated takeoff slots. To avoid this a suboptimal flight plan can be filed, asking for an inefficiently low altitude or a longer less congested route.[4]
Once airborne the part of the pilot's job is to fly as efficiently as possible so he/she might then try to convince air traffic control to allow him to fly closer to the optimum route. This might involve requesting a higher flight level than in the plan or asking for a more direct routing. If the controller does not immediately agree it may be possible to rerequest occasionally until they relent. Alternatively if there has been any bad weather reported in the area a pilot might request a climb or turn to avoid weather. As air traffic controllers do not know the precise location and height of pockets of turbulence, they would not know if the pilot was exaggerating the problem to get a more efficient route.
Even if the pilot does not manage to revert to the optimal route the benefits of being allowed to fly may well outweigh the cost of the suboptimal route.
Additional features
Over and above the various cost-reduction measures mentioned above, flight planning systems may offer extra features to help attract and retain customers:
Other routes
While a flight plan is produced for a specific route, flight dispatchers may wish to consider alternative routes. A flight planning system may produce summaries for say the next 4 best routes, showing zero fuel weight and total fuel for each possibility.
Reclear selection
There may be several possible reclear fixes and initial destinations, and which one is best depends on the weather and the zero fuel weight. A flight planning system can analyse each possibility and select whichever is best for this particular flight.
What-if summaries
On congested routes air traffic control may require that an aircraft fly lower or higher than optimum. The total weight of passengers and cargo might not be known at the time the flight plan is prepared. To allow for these situations a flight planning system may produce summaries showing how much fuel would be needed if the aircraft is a little lighter or heavier, or if it is flying higher or lower than planned. These summaries allow flight dispatchers and pilots to check if there is enough reserve fuel to cope with a different scenario.
Fuel tank distribution
Most commercial aircraft have more than one fuel tank, and an aircraft manufacturer may provide rules as to how much fuel to load into each tank so as to avoid affecting the aircraft centre of gravity. The rules depend on how much fuel is to be loaded, and there may be different sets of rules for different total amounts of fuel. A flight planning system may follow these rules and produce a report showing how much fuel is to be loaded into each tank.
Tankering fuel
When fuel prices differ between airports, it might be worth putting in more fuel where it is cheap, even taking into account the cost of extra trip fuel needed to carry the extra weight. A flight planning system can work out how much extra fuel can profitably be carried. Note that discontinuities due to changes in flight levels can mean that a difference of as little as 100 kg (one passenger with luggage) in zero fuel weight or tankering fuel can make the difference between profit and loss.
Inflight diversion
While en route, an aircraft may be diverted to some airport other than the planned alternate. A flight planning system can produce a new flight plan for the new route from the diversion point and transmit it to the aircraft, including a check that there will be enough fuel for the revised flight.
Inflight refuelling
Military aircraft may refuel in mid-air. Such refuelling is a gradual process rather than instantaneous. Some flight planning systems can allow for the change in fuel and show the effect on each aircraft involved.
Overview and basic terminology
A flight planning system may need to produce more than one flight plan for a single flight:
Summary plan for Air Traffic Control (in FAA and/or ICAO format).
Summary plan for direct download into an onboard flight management system.
Detailed plan for use by pilots.
The basic purpose of a flight planning system is to calculate how much trip fuel is needed in the air navigation process by an aircraft when flying from an origin airport to a destination airport. Aircraft must also carry some reserve fuel to allow for unforeseen circumstances, such as an inaccurate weather forecast, or Air Traffic Control requiring an aircraft to fly at a lower height than optimum due to congestion, or some last-minute passengers whose weight was not allowed for when the flight plan was prepared. The way in which reserve fuel is determined varies greatly, depending on airline and locality. The most common methods are:
USA domestic operations conducted under Instrument Flight Rules: enough fuel to fly to the first point of intended landing, then fly to an alternate airport (if weather conditions require an alternate airport), then for 45 minutes thereafter at normal cruising speed.
percentage of time: typically 10%, i.e. a 10 hour flight needs enough reserve to fly for another hour.
percentage of fuel: typically 5%, i.e. a flight requiring 20,000 kg of fuel needs a reserve of 1,000 kg.
Except for some USA domestic flights, a flight plan normally has an alternate airport as well as a destination airport. The alternate airport is for use in case the destination airport becomes unusable while the flight is in progress (due to weather conditions, a strike, a crash, terrorist activity, etc.). This means that when the aircraft gets near the destination airport, it must still have enough alternate fuel and alternate reserve available to fly on from there to the alternate airport. Since the aircraft is not expected at the alternate airport, it must also have enough holding fuel to circle for a while (typically 30 minutes) near the alternate airport while a landing slot is found. United States domestic flights are not required to have sufficient fuel to proceed to an alternate airport when the weather at the destination is forecast to be better than 2,000-foot (610 m) ceilings and 3 statute miles of visibility; however, the 45-minute reserve at normal cruising speed still applies.
It is often considered a good idea to have the alternate some distance away from the destination (e.g. 100 miles) so that bad weather is unlikely to close both the destination and the alternate; distances up to 600 miles (970 km) are not unknown. In some cases the destination airport may be so remote (e.g. Pacific island) that there is no feasible alternate airport; in such a situation an airline may instead include enough fuel to circle for 2 hours near the destination, in the hope that the airport will become available again within that time.
There is often more than one possible route between two airports. Subject to safety requirements, commercial airlines generally wish to minimise costs by appropriate choice of route, speed, and height.
Various names are given to weights associated with an aircraft and/or the total weight of the aircraft at various stages.
Payload is the total weight of the passengers, their luggage, and any cargo. A commercial airline makes its money by charging to carry payload.
Operating weight empty is the basic weight of the aircraft when ready for operation, including crew but excluding any payload or fuel.
Zero fuel weight is the sum of operating weight empty and payload, i.e. the laden weight of an aircraft, excluding any fuel.
Ramp weight is the weight of an aircraft at the terminal building when ready for departure. This includes the zero fuel weight and all required fuel.
Brake release weight is the weight of an aircraft at the start of a runway, just prior to take-off. This is the ramp weight minus any fuel used for taxiing. Major airports may have runways which are about two miles (3 km) long, so merely taxiing from the terminal to the end of the runway might consume up to a ton of fuel. After taxiing the pilot lines up the aircraft with the runway and puts the brakes on. On receiving take-off clearance, the pilot throttles up the engines and releases the brakes to start accelerating along the runway in preparation for taking off.
Take off weight is the weight of an aircraft as it takes off part way along a runway. Few flight planning systems calculate the actual take-off weight; instead, the fuel used for taking off is counted as part of the fuel used for climbing up to the normal cruise height.
Landing weight is the weight of an aircraft as it lands at the destination. This is the brake release weight minus the trip fuel burnt. It includes the zero fuel weight and all alternate, holding, and reserve fuel.
When twin-engine aircraft are flying across oceans, deserts, etc. the route must be carefully planned so that the aircraft can always reach an airport, even if one engine fails. The applicable rules are known as ETOPS (Extended-range Twin-engine Operational Performance Standards). The general reliability of the particular type of aircraft and its engines and the maintenance quality of the airline are taken into account when specifying for how long such an aircraft may fly with only one engine operating (typically from 1 to 3 hours).
Flight planning systems must be able to cope with aircraft flying below sea level, which will often result in a negative altitude. For example Amsterdam Schiphol Airport has an elevation of -3 metres. The surface of the Dead Sea is 417 metres below sea level, so low level flights in this vicinity can be well below sea level.[2]
Units of measurement
Flight plans use an unusual mixture of metric and non-metric units of measurement. The particular units used may vary by aircraft, by airline, and by location (e.g. different height units may be used at different points during a single flight).
Distance units
Distances are always measured in nautical miles, as calculated at a height of 32,000 feet (9,800 m), with due allowance for the fact that the earth is an oblate spheroid rather than a perfect sphere.
Aviation charts always show distances as rounded to the nearest nautical mile, and these are the distances which are shown on a flight plan. Flight planning systems may need to use the unrounded values in their internal calculations for improved accuracy.
Fuel units
There are a variety of ways in which fuel can be measured, depending mainly on the gauges fitted to a particular aircraft. The most common unit of fuel measurement is kilograms; other possible measures include pounds, UK gallons, US gallons, and litres. When fuel is measured by weight the specific gravity of the fuel must be taken into account when checking tank capacity. Specific gravity may vary depending on the location and the supplier.
There has been at least one occasion on which an aircraft ran out of fuel due to an error in converting between kilograms and pounds. In this particular case the flight crew managed to glide to a nearby airport and land safely.
Many airlines request that fuel quantities be rounded to a multiple of 10 or 100 units. This can cause some interesting rounding problems, especially when subtotals are involved. Safety issues must also be considered when deciding whether to round up or down.
Height units
The actual height of an aircraft is based on use of a pressure altimeter - see flight level for more detail. The heights quoted here are thus the nominal heights under standard conditions of temperature and pressure rather than the actual heights. All aircraft operating on flight levels calibrate altimeters to the same standard setting regardless of the actual sea level pressure, so little risk of collision arises.
In most areas, height is reported as a multiple of 100 feet (30 m), i.e. A025 is nominally 2,500 feet (760 m). When cruising at higher altitudes aircraft adopt Flight Levels (FL). Flight Levels are altitudes corrected and calibrated against the International Standard Atmosphere (ISA). These are expressed as a three figure group e.g. FL320 is 32,000 Feet (ISA).
In most areas vertical separation between aircraft is either 1000 or 2,000 feet (610 m).
In China and some neighbouring areas, height is handled using metres. Vertical separation between aircraft is either 300 metres or 600 metres (about 1.6% less than 1000 or 2000 feet).
Up until 1999, the vertical separation between aircraft flying on the same airway was 2,000 feet (610 m). Since then there has been a phased introduction around the world of Reduced Vertical Separation Minimum (RVSM). This cuts the vertical separation to 1,000 feet (300 m) between about 29,000 feet (8,800 m) and 41,000 feet (the exact limits vary slightly from place to place). Since most jet aircraft operate between these heights, this measure effectively doubles the available airway capacity. To use RVSM, aircraft must have certified altimeters, and autopilots must meet more accurate standards.
Speed units
Aircraft cruising at lower altitudes normally use knots as the primary speed unit, while aircraft that are higher (above Mach Crossover Altitude) normally use Mach number as the primary speed unit, though flight plans often include the equivalent speed in knots as well (the conversion includes allowance for temperature and height). In a flight plan, a Mach number of "Point 82" means that the aircraft is travelling at 0.820 (82%) the speed of sound.
The widespread use of Global Positioning Systems (GPS) allows cockpit navigation systems to provide air speed and ground speed more or less directly.
Another method of obtaining speed and position is the Inertial Navigation System (INS), which keeps track a vehicle's acceleration using gyroscopes and linear accelerometers; this information can then be integrated in time to obtain speed and position, as long as the INS was properly calibrated before departure. INS has been present in civil aviation for a few decades and is mostly used in medium to large aircraft as the system is fairly complex.
If neither GPS or INS are used, the following steps are required to obtain speed information:
An airspeed indicator is used to measure indicated airspeed (IAS) in knots.
IAS is converted to calibrated airspeed (CAS) using an aircraft-specific correction table.
CAS is converted to equivalent airspeed (EAS) by allowing for compressibility effects.
EAS is converted to true airspeed (TAS) by allowing for density altitude, i.e. height and temperature.
TAS is converted to ground speed by allowing for any head or tail wind.
Weight units
The weight of an aircraft is most commonly measured in kilograms, but may sometimes be measured in pounds, especially if the fuel gauges are calibrated in pounds or gallons. Many airlines request that weights be rounded to a multiple of 10 or 100 units. Great care is needed when rounding to ensure that physical constraints are not exceeded.
When chatting informally about a flight plan, approximate weights of fuel and/or aircraft may be referred to in tons. This 'ton' is generally either a metric tonne or a UK long ton, which differ by less than 2%, or a short ton, which is about 10% less.
Describing a route
A route is a description of the path followed by an aircraft when flying between airports. Most commercial flights will travel from one airport to another, but private aircraft, commercial sightseeing tours, and military aircraft may often do a circular or out-and-back trip and land at the same airport from which they took off.
Components
Aircraft fly on airways under the direction of Air Traffic Control. An airway has no physical existence, but can be thought of as a 'motorway' in the sky. On an ordinary motorway, cars use different lanes to avoid collisions, while on an airway, aircraft fly at different flight levels to avoid collisions. One can often see planes passing directly above or below one's own. Charts showing airways are published and are usually updated once a month coinciding with the AIRAC cycle. AIRAC (Aeronautical Information Regulation and Control) occurs every fourth Thursday when every country publishes their changes, which are usually to airways.
Each airway starts and finishes at a waypoint, and may contain some intermediate waypoints as well. Waypoints use five letters, e.g., PILOX, and those that double as non-directional beacons use three or two: TNN, WK. Airways may cross or join at a waypoint, so an aircraft can change from one airway to another at such points. A complete route between airports often uses several airways. Where there is no suitable airway between two waypoints, and using airways would result in a somewhat roundabout route, air traffic control may allow a direct waypoint to waypoint routing which does not use an airway (often abbreviated in flight plans as 'DCT').
Most waypoints are classified as compulsory reporting points, i.e. the pilot (or the onboard flight management system) reports the aircraft position to air traffic control as the aircraft passes a waypoint. There are two main types of waypoints:
A named waypoint appears on aviation charts with a known latitude and longitude. Such waypoints over land often have an associated radio beacon so that pilots can more easily check where they are. Useful named waypoints are always on one or more airways.
A geographic waypoint is a temporary position used in a flight plan, usually in an area where there are no named waypoints, e.g. most oceans in the southern hemisphere. Air traffic control require that geographic waypoints have latitudes and longitudes which are a whole number of degrees.
Note that airways do not connect directly to airports.
After take-off an aircraft follows a Departure Procedure (SID or Standard Instrument Departure) which defines a pathway from an airport runway to a waypoint on an airway, so that an aircraft can join the airway system in a controlled manner. Most of the climb portion of a flight will take place on the SID.
Before landing an aircraft follows an Arrival Procedure (STAR or Standard Terminal Arrival Route) which defines a pathway from a waypoint on an airway to an airport runway, so that aircraft can leave the airway system in a controlled manner. Much of the descent portion of a flight will take place on a STAR.
Airline routes between Los Angeles and Tokyo approximately follow a direct great circle route (top), but use the jet stream (bottom) when heading eastwardsSpecial routes known as ocean tracks are used across some oceans, mainly in the northern hemisphere to increase traffic capacity on busy routes. Unlike ordinary airways which change infrequently, ocean tracks change twice a day, so as to take advantage of any favourable winds. Flights going with the jet stream may be an hour shorter than those going against it. Ocean tracks often start and finish perhaps a hundred miles offshore at named waypoints to which a number of airways connect. Tracks across northern oceans are suitable for east-west or west-east flights, which constitute the bulk of the traffic in these areas.
Complete routes
There are a number of ways of constructing a route. All scenarios using airways use SIDs and STARs for departure and arrival. Any mention of airways might include a very small number of 'direct' segments to allow for situations when there are no convenient airway junctions. In some cases political considerations may influence the choice of route (e.g. aircraft from one country cannot overfly some other country).
Airway(s) from origin to destination. Most flights over land fall into this category.
Airway(s) from origin to an ocean edge, then an ocean track, then airway(s) from ocean edge to destination. Most flights over northern oceans fall into this category.
Airway(s) from origin to an ocean edge, then a free-flight area across an ocean, then airway(s) from ocean edge to destination. Most flights over southern oceans fall into this category
Free-flight area from origin to destination. This is a relatively uncommon situation for commercial flights.
Even in a free-flight area, air traffic control still requires a position report about once an hour. Flight planning systems organise this by inserting geographic waypoints at suitable intervals. For a jet aircraft these intervals are 10 degrees of longitude for east-bound or west-bound flights and 5 degrees of latitude for north-bound or south-bound flights. In free-flight areas commercial aircraft normally follow a least-time-track so as to use as little time and fuel as possible. A great circle route would have the shortest ground distance, but is unlikely to have the shortest air-distance, due to the effect of head or tail winds. A flight planning system may have to do quite a lot of analysis in order to determine a good free-flight route.
Fuel calculation
Calculation of fuel requirements (especially trip fuel and reserve fuel) is the most safety-critical aspect of flight planning. This calculation is somewhat complicated:
Rate of fuel burn depends on ambient temperature, aircraft speed, and aircraft altitude, none of which are entirely predictable.
Rate of fuel burn also depends on airplane weight, which changes as fuel is burned.
Some iteration is generally required due to the need to calculate interdependent values, e.g. reserve fuel is often calculated as a percentage of trip fuel, but trip fuel can't be calculated until the total weight of the aircraft is known, including the weight of the reserve fuel!
Considerations
Fuel calculation must take many factors into account.
Weather forecasts
The air temperature affects the efficiency/fuel consumption of aircraft engines. The wind may provide a head or tail wind component which in turn will increase or decrease the fuel consumption by increasing or decreasing the air distance to be flown.
By agreement with the International Civil Aviation Organization, there are two national weather centres (in U.S.A. and U.K.) which provide worldwide weather forecasts for civil aviation in a format known as GRIB weather. These forecasts are generally issued every 6 hours, and cover the next 36 hours at intervals of 6 hours. Each 6-hour forecast covers the whole world using gridpoints located at intervals of 75 miles (121 km) or less. At each grid point the weather (wind speed, wind direction, air temperature) is supplied at 9 different heights ranging from about 4,500 feet (1,400 m) up to about 55,000 feet (17,000 m).
Aircraft seldom fly exactly through weather gridpoints or at the exact heights at which weather predictions are available, so some form of horizontal and vertical interpolation is generally needed. For 75-mile (121 km) intervals, linear interpolation is satisfactory. GRIB format superseded the earlier ADF format in 1998/9. The ADF format used 300-mile (480 km) intervals; this interval was large enough to miss some storms completely, so calculations using ADF predicted weather were often not as accurate as those which can be produced using GRIB weather.
Routes and flight levels
The particular route to be flown determines the ground distance to cover, while winds on that route determine the air distance to be flown. Each inter-waypoint portion of an airway may have different rules as to which flight levels may be used. Total aircraft weight at any point determines the highest flight level which can be used. Cruising at a higher flight level generally requires less fuel than at a lower flight level, but extra climb fuel may be needed to get up to the higher flight level (it is this extra climb fuel and the different fuel consumption rate which cause discontinuities).
Physical constraints
Almost all the weights mentioned above in 'Overview and basic terminology' may be subject to minimum and/or maximum values. Due to stress on the wheels and undercarriage when landing, the maximum safe landing weight may be considerably less than the maximum safe brake-release weight. In such cases, an aircraft which encounters some emergency and has to land straight after taking off may have to circle for a while to use up fuel, or else jettison some fuel, or else land immediately and risk having the undercarriage collapse.
Also, the fuel tanks have some maximum capacity. On some occasions, commercial flight planning systems find that an impossible flight plan has been requested. The aircraft can't possibly reach the intended destination, even with no cargo or passengers, since the fuel tanks are just not big enough to hold the amount of fuel needed; it would appear that some airlines are over-optimistic at times, perhaps hoping for a (very) strong tailwind.
Fuel consumption rate
The rate of fuel consumption for aircraft engines depends on: air temperature, height as measured by air pressure, aircraft weight, aircraft speed relative to the air, and any increased consumption as compared with brand-new engines due to engine age and/or poor maintenance (an airline can estimate this degradation by comparing actual and predicted fuel burn). Note that a large aircraft such as a jumbo jet may burn up to 80 tons of fuel on a 10 hour flight, so there is a substantial weight change during the flight.
Calculation
The weight of fuel forms a significant part of the total weight of an aircraft, so any fuel calculation must take into account the weight of any fuel not yet burnt. Instead of trying to predict fuel load not yet burnt, a flight planning system can handle this situation by working backwards along the route, starting at the alternate, going back to the destination, and then going back waypoint by waypoint to the origin.
A more detailed outline of the calculation follows. Several (possibly many) iterations are usually required, either to calculate interdependent values such as reserve fuel and trip fuel, or to cope with situations where some physical constraint has been exceeded. In the latter case it is usually necessary to reduce the payload (less cargo or less passengers). Some flight planning systems use elaborate systems of approximate equations to simultaneously estimate all the changes required; this can greatly reduce the number of iterations needed.
If an aircraft lands at the alternate, in the worst case it can be assumed to have no fuel left (in practice there will be enough reserve fuel left to at least taxi off the runway). Hence a flight planning system can calculate alternate holding fuel on the basis that the final aircraft weight is just the zero fuel weight. Since the aircraft is circling while holding there is no need to take wind into account for this or any other holding calculation.
For the flight from destination to alternate, a flight planning system can calculate alternate trip fuel and alternate reserve fuel on the basis that the aircraft weight on reaching the alternate is zero fuel weight plus alternate holding.
A flight planning system can then calculate any destination holding on the basis that the final aircraft weight is zero fuel weight plus alternate holding plus alternate fuel plus alternate reserve.
For the flight from origin to destination, the weight on arrival at the destination can be taken as zero fuel weight plus alternate holding plus alternate fuel plus alternate reserve plus destination holding. A flight planning system can then work back along the route, calculating the trip fuel and reserve fuel one waypoint at a time, with the fuel required for each inter-waypoint segment forming part of the aircraft weight for the next segment to be calculated.
At each stage and/or at the end of the calculation, a flight planning system must carry out checks to ensure that physical constraints (e.g. maximum tank capacity) have not been exceeded. Problems mean that either the aircraft weight must be reduced in some fashion, or else the calculation must be abandoned.
An alternative approach to fuel calculation is to calculate alternate and holding fuel as above, and obtain some estimate of the total trip fuel requirement, either based on previous experience with that route and aircraft type, or by using some approximate formula; neither method can take much account of weather. Calculation can then proceed forwards along the route waypoint by waypoint. On reaching the destination, the actual trip fuel can be compared with the estimated trip fuel, a better estimate made, and the calculation repeated as required.
Cost reduction
Commercial airlines generally wish to keep the cost of a flight as low as possible. There are three main factors which contribute to the cost:
amount of fuel needed (to complicate matters, fuel may cost different amounts at different airports),
actual flying time affects depreciation charges and maintenance schedules etc.,
overflight charges are levied by each country the aircraft flies over (notionally to cover air traffic control costs).
Different airlines have different views as to what constitutes a least cost flight:
Least cost based only on time.
Least cost based only on fuel.
Least cost based on a balance between fuel and time.
Least cost based on fuel costs and time costs and overflight charges.
[edit] Basic improvements
For any given route, a flight planning system can reduce cost by finding the most economical speed at any given height, and by finding the best height(s) to use based on the predicted weather. Such local optimisation can be done on a waypoint by waypoint basis.
Commercial airlines do not want an aircraft to change height too often (among other things, it may make it more difficult for the cabin crew to serve meals), so they often specify some minimum time between optimisation-related flight level changes. To cope with such requirements a flight planning system must be capable of non-local height optimisation by simultaneously taking a number of waypoints into account, along with the fuel costs for any short climbs that may be required.
When there is more than one possible route between the origin and destination airports, the task facing a flight planning system becomes more complicated, since it must now consider many routes in order to find the best available route. Many situations have tens or even hundreds of possible routes, and there are some situations with over 25,000 possible routes (e.g. London to New York with free-flight below the track system). The amount of calculation required to produce an accurate flight plan is so substantial that it is not feasible to examine every possible route in detail. A flight planning system must have some fast way of cutting the number of possibilities down to a manageable number before undertaking a detailed analysis.
Reserve reduction
From an accountant's viewpoint, the provision of reserve fuel costs money (the fuel needed to carry the hopefully unused reserve fuel). Techniques known variously as reclear or redispatch or decision point procedure have been developed, which can greatly reduce the amount of reserve fuel needed while still maintaining all required safety standards. These techniques are based on having some specified intermediate airport to which the flight can divert if necessary;[1] in practice such diversions are rare. The use of such techniques can save several tons of fuel on long flights, or it can increase the payload carried by a similar amount.[3]
A reclear flight plan has two destinations. The final destination airport is where the flight is really going to, while the initial destination airport is where the flight will divert to if more fuel is used than expected during the early part of the flight. The waypoint at which the decision is made as to which destination to go to is called the reclear fix or decision point. On reaching this waypoint, the flight crew make a comparison between actual and predicted fuel burn and check how much reserve fuel is available. If there is sufficient reserve fuel then the flight can continue to the final destination airport, otherwise the aircraft must divert to the initial destination airport.
The initial destination is positioned so that less reserve fuel is needed for a flight from the origin to the initial destination than for a flight from the origin to the final destination. Under normal circumstances little if any of the reserve fuel is actually used, so when the aircraft reaches the reclear fix it still has (almost) all the original reserve fuel on board, which is enough to cover the flight from the reclear fix to the final destination.
The idea of reclear flights was first published in 'Boeing Airliner' (1977) by Boeing engineers David Arthur and Gary Rose.[3] The original paper contains a lot of magic numbers relating to the optimum position of the reclear fix, etc. These numbers apply only to the specific type of aircraft considered, for a specific reserve percentage, and take no account of the effect of weather. The fuel savings due to reclear depend on three factors:
The maximum achievable saving depends on the position of the reclear fix. This position can't be determined theoretically since there are no exact equations for trip fuel and reserve fuel. Even if it could be determined exactly, there may not be a waypoint at the right place anyway.
One factor identified by Arthur and Rose which helps achieve the maximum possible saving is to have an initial destination which is positioned so that descent to the initial destination starts immediately after the reclear fix. This is beneficial because it minimises the reserve fuel needed between reclear fix and initial destination, and hence maximises the amount of reserve fuel available at the reclear fix.
The other factor which is also helpful depends on the positioning of the initial alternate airport.
Filing Suboptimal Plans
Despite all the effort taken to optimise flight plans there are certain circumstances where it is advantageous to file suboptimal plans. In busy airspace with a number of competing aircraft, the optimum routes and preferred altitudes may well be oversubscribed. This problem can be made worse by busy periods, for example where everyone wants to arrive at an airport as soon as it opens for the day. If all the aircraft file an optimal flight plan then to avoid overloading, air traffic control may refuse permission for some of the flight plans or delay the allocated takeoff slots. To avoid this a suboptimal flight plan can be filed, asking for an inefficiently low altitude or a longer less congested route.[4]
Once airborne the part of the pilot's job is to fly as efficiently as possible so he/she might then try to convince air traffic control to allow him to fly closer to the optimum route. This might involve requesting a higher flight level than in the plan or asking for a more direct routing. If the controller does not immediately agree it may be possible to rerequest occasionally until they relent. Alternatively if there has been any bad weather reported in the area a pilot might request a climb or turn to avoid weather. As air traffic controllers do not know the precise location and height of pockets of turbulence, they would not know if the pilot was exaggerating the problem to get a more efficient route.
Even if the pilot does not manage to revert to the optimal route the benefits of being allowed to fly may well outweigh the cost of the suboptimal route.
Additional features
Over and above the various cost-reduction measures mentioned above, flight planning systems may offer extra features to help attract and retain customers:
Other routes
While a flight plan is produced for a specific route, flight dispatchers may wish to consider alternative routes. A flight planning system may produce summaries for say the next 4 best routes, showing zero fuel weight and total fuel for each possibility.
Reclear selection
There may be several possible reclear fixes and initial destinations, and which one is best depends on the weather and the zero fuel weight. A flight planning system can analyse each possibility and select whichever is best for this particular flight.
What-if summaries
On congested routes air traffic control may require that an aircraft fly lower or higher than optimum. The total weight of passengers and cargo might not be known at the time the flight plan is prepared. To allow for these situations a flight planning system may produce summaries showing how much fuel would be needed if the aircraft is a little lighter or heavier, or if it is flying higher or lower than planned. These summaries allow flight dispatchers and pilots to check if there is enough reserve fuel to cope with a different scenario.
Fuel tank distribution
Most commercial aircraft have more than one fuel tank, and an aircraft manufacturer may provide rules as to how much fuel to load into each tank so as to avoid affecting the aircraft centre of gravity. The rules depend on how much fuel is to be loaded, and there may be different sets of rules for different total amounts of fuel. A flight planning system may follow these rules and produce a report showing how much fuel is to be loaded into each tank.
Tankering fuel
When fuel prices differ between airports, it might be worth putting in more fuel where it is cheap, even taking into account the cost of extra trip fuel needed to carry the extra weight. A flight planning system can work out how much extra fuel can profitably be carried. Note that discontinuities due to changes in flight levels can mean that a difference of as little as 100 kg (one passenger with luggage) in zero fuel weight or tankering fuel can make the difference between profit and loss.
Inflight diversion
While en route, an aircraft may be diverted to some airport other than the planned alternate. A flight planning system can produce a new flight plan for the new route from the diversion point and transmit it to the aircraft, including a check that there will be enough fuel for the revised flight.
Inflight refuelling
Military aircraft may refuel in mid-air. Such refuelling is a gradual process rather than instantaneous. Some flight planning systems can allow for the change in fuel and show the effect on each aircraft involved.
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