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Flight planning is the process of producing a flight plan which describes an aircraft flight. The planning done by a private pilot flying a small single-engined aircraft may be very different from that done for a commercial airline using a multi-engine plane carrying hundreds of passengers. Much of this article currently applies to the latter situation.

The most safety-critical aspect of flight planning is the fuel calculation: enough fuel must be carried to ensure that the flight can be completed safely, including some allowance for emergencies or unexpected happenings. Accurate weather predictions are needed so that due allowance can be made for head winds or tail winds. When aircraft with only two engines are flying across oceans, they have to satisfy extra safety rules to ensure that such aircraft can reach some emergency airport if one engine fails.

Flight planning must be done in accordance with the requirements of air traffic control to minimse the risk of collision with other aircraft. In most parts of the world, aircraft flying in controlled airspace must stick to predetermined routes, known as airways, even if such routes are not as economical as a more direct flight. On an airway, aircraft must fly at specified heights (known as flight levels), usually with a vertical separation of either 1000 or 2000 feet. The allowable heights depend on the route being flown and the direction of travel.

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. Flight planning used to be done by hand, which placed very severe limits on the possibilities which could be considered. The current use of computers for flight planning provides more capacity for optimisation and cost reduction.

Some airlines have their own internal flight planning system while other airlines use a flight planning system provided either by another airline or by some external vendor as a bureau service.

A single flight may have more than one associated flight plan:

• 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.

Basic terminology

names for airports and fuel

The basic purpose of a flight planning system is to calculate how much trip fuel is needed 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.

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 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 fuel to circle for a while (typically 30 minutes) near the alternate airport while a landing slot is found. The fuel allocated for circling is known as holding fuel.

zero-fuel weight

This is the laden weight of an aircraft, excluding any fuel. Components of zero-fuel weight include:

• Empty weight of the aircraft ready for operation (this normally includes the weight of the crew).
• Weight of the payload, which includes:
  • weight of passengers and their luggage,
  • weight of any cargo being carried.

brake-release weight

This is the weight of an aircraft at the start of a runway, just prior to take-off. After taxiing out from the terminal building, the pilot lines up the aircraft with the runway and puts the brakes on. On receiving take-off clearance, the pilot revs up the engines and releases the brakes to start accelerating along the runway in preparation for taking off.

Note that brake-release weight is often confused with take-off weight, which 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.

Units of measurement

Flight plans use a strange 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, 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, i.e. FL320 is nominally 32,000 feet. Vertical separation between aircraft is either 1000 or 2000 feet.

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).

Speed units

Aircraft with propellors normally use knots as the primary speed unit, while aircraft powered by jet engines 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 820 means that the aircraft is travelling at 0.820 of 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.

If GPS is not 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.

Navigation terminology

airway

Worldwide there a large number of named official airways, along which aircraft fly 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 heights to avoid collisions.

Each airway starts and finishes at a waypoint. There may be several waypoints along an airway. 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. Note that airways do not connect directly to airports - see Standard Instrument Departure and Standard Terminal Arrival Route below.

Charts showing airways are published once a year. Changes to airways are published once a month.

ocean tracks

As the name implies, an ocean track is a possible route across an ocean, although there are proposals to use the same idea for some routes in south-east Asia and Australia. Ocean tracks are used mainly in the northern hemisphere to increase traffic capacity on busy routes across oceans. 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.

segment

The connection between one waypoint and the next is known as a segment. Each segment on an airway has an associated cruise table which defines the heights at which an aircraft may use that segment. Most airways are two-way, so the cruise table defines different heights depending on the direction of travel.

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 segment to be specified as 'direct', often abbreviated as 'DCT'; this means that an aircraft is flying directly from one waypoint to another without using an airway.

Standard Instrument Departure

This may be referred to as a SID or as a Departure Procedure. A SID 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.

Standard Terminal Arrival Route

This may be referred to as a STAR or Arrival Procedure. A STAR 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.

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.

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.

What is 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.

There are a number of ways of constructing a route. To save repetition, all scenarios below are generally assumed to 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.

• 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 require 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 (LTT) 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.

Safety considerations

Reserve fuel

Aircraft must also carry some reserve fuel to allow for unforeseen circumstances, e.g. Air Traffic Control may require an aircraft to fly at a lower height than optimum due to congestion, or there may be 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:

• U.S.A. domestic: enough fuel to circle for 45 minutes at the destination.
• percentage of time: typically 10%, i.e. for a 10 hour flight need enough reserve to fly for another hour.
• percentage of fuel: typically 5%, i.e. for a flight requiring 20,000 Kg of fuel need a reserve of 1,000 Kg.

A few airlines calculate reserve fuel by all of the above methods and then select the method which gives the least amount of reserve fuel. Airlines may in addition specify some minimum and/or maximum amount of reserve fuel to be used.

The introduction of reserve fuel can add a chicken and egg situation to the flight plan calculation: first calculate the trip fuel based on the aircraft weight, then add on say 5% of fuel as reserve, which means the aircraft is now heavier so extra trip fuel is needed to carry the reserve, which means there is now more trip fuel than originally calculated so further reserve fuel is needed for this extra trip fuel, which means the aircraft is now even heavier so a little more trip fuel is needed to carry the further reserve, etc, etc.

Alternate and holding

Note that U.S.A. domestic flights do not need to have an alternate airport - the FAA consider that there are so many airports available that the U.S.A. domestic reserve provides enough fuel to reach some other airport.

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 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.

Note that the trip fuel from destination to alternate must include enough fuel to carry the holding fuel, and that the trip fuel from origin to destination must include enough fuel to carry the alternate and holding fuel, and the reserve fuel for the alternate sector as well. Especially for shorter flights, the fuel needed for alternate and holding may exceed the actual trip fuel.

Congestion, airways, flight levels

The basic reason for using airways and flight levels is to keep the situation in the air simple enough for Air Traffic Control to manage so as to reduce the risk of collisions.

Up until 1999, the vertical separation between aircraft flying on the same airway was 2000 feet. Since then there has been a phased introduction around the world of Reduced Vertical Separation Minimum (RVSM). This cuts the vertical separation to 1000 feet between about 29,000 feet 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.

Another method for increasing capacity is to decrease the distance between successive aircraft flying along the same route. This method is known as fixed Mach technique, and requires that all the aircraft involved fly at exactly the same speed (Mach number). Again, to use this method, autopilots must meet more accurate standards.

Across oceans

When twin-engine aircraft are flying across oceans, 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).

Airline responsibility

It is up to the airline to ensure that all the airports involved can actually handle the aircraft being used, e.g. an airport with a 5,000 foot runway can't handle a jumbo jet. In particular, the airline is responsible for checking that any specified alternate is likely to be open, available, and usable, at the time the aircraft might be expected to arrive there.

If there are political considerations involved (e.g. aircraft from one country can't overfly some other country), then it is up to the airline to specify a route which avoids any problems.

Fuel calculation

This calculation must take the following into account:

• ever-changing operational and safety regulations, both national and international,
• physical constraints such as the maximum fuel tank capacity of the aircraft,
• aircraft performance details (e.g. fuel consumption while climbing or cruising),
• the particular route to be flown,
• the height(s) at which to fly along the route.
• predicted weather conditions along the route to be flown,
• weight of the aircraft excluding fuel: zero-fuel weight.

Physical constraints

There are a number of physical constraints which apply to aircraft:

• Maximum fuel tank capacity.
• Minimum and maximum zero-fuel weight.
• Maximum weight at the terminal building before taxiing to the runway for take-off.
• Maximum weight at the start of the runway just before take-off (known as brake-release weight).
• Maximum safe landing weight.

If one or more of these limits are exceeded, the only solution is to reduce the amount of cargo or the number of passengers being carried.

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 (charter) airlines are over-optimistic at times, perhaps hoping for a (very) strong tailwind.

Due to stress on the 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 has to land immediately after taking off may have to circle for a while to use up fuel, or else jettison some fuel.

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 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 up to about 55,000 feet.

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 intervals, linear interpolation is satisfactory. GRIB format superceded the earlier ADF format in 1998/9. The ADF format used 300-mile intervals, which was large enough to miss some storms completely, so calculations using ADF predicted weather were not always entirely accurate.

Weight

The total weight of an aircraft affects the fuel consumption in several ways; note that this weight at any time includes the weight of the fuel which has not yet been burnt.

• At any given height, fuel consumption increases with weight.
• An aircraft uses less fuel at greater heights (less air resistance).
• The maximum height at which an aircraft can fly increases as its weight decreases.

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. As the flight progresses, the aircraft becomes lighter and hence is able to cruise at a higher flight level, often with a lower fuel consumption.

Calculation

There are no simple equations from which to calculate how much fuel is needed, especially as the use of flight levels may introduce discontinuities. Towards the end of a long flight, an aircraft has burnt off a lot of fuel so it may be more economical to fly at a higher flight level. But climbing to a higher level requires some additional step climb fuel which shows up as a brief increase in fuel consumption.

The rate of fuel consumption for aircraft engines depends on five factors:

• air temperature
• height (more precisely: air pressure)
• aircraft weight
• aircraft speed relative to the air
• 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 the effect of wind is to alter the air distance to be flown: a head wind increases this distance while a tail wind decreases this distance. It is this change in air distance which causes more or less fuel to be used.

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. The easiest way to do this is to calculate the fuel by working backwards along the route. Any stage which lasts for more than 15 to 30 minutes may have to be split into shorter substages to make proper allowance for the extra fuel weight at each substage.

• Start at the alternate with the zero-fuel weight (no fuel on board). Calculate how much holding fuel is needed for a given holding time. Since the aircraft is circling there is no need to take wind into account for this calculation.

• At the alternate the aircraft weight is now zero-fuel weight plus alternate holding. Use this weight as a basis for calculating the alternate fuel and alternate reserve for the flight from destination to alternate.

• At the destination the weight is now zero-fuel weight plus alternate holding plus alternate fuel plus alternate reserve. Calculate any holding required at the destination.

• At the destination the weight is now zero-fuel weight plus alternate holding plus alternate fuel plus alternate reserve plus destination holding. Use this weight as a basis for calculating the trip fuel and reserve fuel for the flight from origin to destination, working back one waypoint at a time, with the aircraft getting heavier at each waypoint.

There are several complicating factors:

• • Reserve fuel generally depends either on trip time or trip fuel, and these in turn depend on aircraft weight which depends to some extent on reserve fuel!
  • Fuel consumption rate for descent is less than for cruising.
  • The total descent fuel weight depends on the length of the descent which depends on the final cruise height, which depends on the final cruise weight, which depends on the descent fuel weight!
  • At any one point there is some most economical speed at which to fly, depending on temperature, height, weight, etc.
  • At any one point the best fuel economy is generally attained by flying at the maximum flyable height, but when wind is taken into account it may be more economical to fly at some less economical height to take advantage of more favourable winds. Any such vertical optimisation to take wind into account may need to consider any limits imposed by an airline as to how frequently the airline is prepared to tolerate a height change (e.g. climbing or descending makes it more difficult for cabin crew to serve meals).
  • Any climb to change to a higher flight level height will incur a step climb fuel cost which introduces a discontinuity into the situation.
  • Fuel consumption rate for climb is much more than for cruising, especially in the lower part of the climb which includes the fuel needed for take-off.
  • At any stage it may be discovered that some physical constraint has been exceeded, in which case the payload has to be reduced by some appropriate amount and the calculation restarted.

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).

What is best?

Different airlines have different views as to what is a 'best' flight:

• Shortest time, i.e. least time costs.
• Least fuel, i.e. least fuel costs.
• Least cost based on fuel costs and time costs.
• Least cost based on fuel costs and time costs and overflight charges.

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.

Route selection

When there is more than one possible route between the origin and destination airports, the task facing a flight planning system becomes more complicated. Many situations have tens or even hundreds of possible routes, and there are some situations with over 6,000 possible routes. 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 accountants 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; 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.

Reclear/redispatch flight

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. Both destination airports normally have alternates.

The waypoint at which the decision is made as to which destination to go to is called the reclear fix. On reaching the reclear fix, the flight crew make a comparison between actual and predicted fuel burn. If sufficient reserve fuel is available then the flight can continue to the final destination airport, otherwise the aircraft must divert to the initial destination airport.

A flight planning system calculates two flight plans (one for each destination), with adjustments so that the two plans are identical as far as the reclear fix in terms of airways, waypoints, fuel consumption, speed, flight levels, etc. The initial destination is positioned so that the flying distance, trip fuel, etc. for a flight from the origin to the initial destination are somewhat less than those for a flight from the origin to the final destination.

The aircraft is only supplied with enough reserve fuel to cover the flight to the initial destination, which is less than that needed to cover the flight 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. But the distance etc. from reclear fix to final destination is a lot less than that from origin to final destination, so there is enough reserve fuel on board to cover the flight from 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. 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.

Because there are no equations relating distance, weather, and reserve rate to fuel consumption, it is not possible to find an exact equation for the optimum position of the reclear fix. One factor which helps save fuel is to find an initial destination which is positioned so that descent to the initial destination starts immediately after the reclear fix.

Additional features

Flight planning systems may offer extra features:

• 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.
• 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.
• Inflight diversion. While en route, an aircraft may be diverted to some other airport. Produce a new flight plan for the new route from the diversion point and transmit it to the aircraft.
• What-if summaries. How much fuel would be needed if the aircraft is a little lighter or heavier, or if it is flying one Flight Level higher or lower than planned.
• Other routes. What are the (say 4) next best routes, and how much fuel would be needed for each of these.
• Inflight refuelling. Military aircraft may refuel in mid-air. Can a flight plan show the effect on each aircraft involved.

Trivia

Flight planning systems must be able to cope with aircraft flying below sea level, e.g. Amsterdam Schiphol Airport has an elevation of -3 metres. The surface of the Dead Sea is nearly 400 metres below sea level.

See also

• Air navigation
• Air safety
• Air speed
• Climb
• Cruise
• Descent
• Flight plan
• Holding
• Instrument flight rules
• Landing
• Runway
• Take-off
• Taxiing
• Visual flight rules

References

Boeing Airliner (1977): "REDISPATCH for fuel savings and increased payload". Arthur & Rose.

External links

Federal Aviation Regulations: Sec 121.631 (re redispatch)

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