What does a commercial pilot need to consider when planning their flight? We give you an insight from Aileron’s very own line flying pilots, in nine simple steps.
1. Departure and arrival airports
To plan a flight, you’ll need to know where you are taking off from and arriving at, in particular you’ll need to know your runways. Air Traffic Control (ATC) will decide on which runway will be used, but a pilot can make their own judgement on which one it will be depending on the forecast winds. Normally it will be the runway with the most head wind, but sometimes for performance reasons pilots might decide to use a runway with a slight tail wind. Sometimes a flight may appear to take-off in the wrong direction for the destination due to the runway that is allocated, and this could mean planning for more fuel.
2. Taxi times
This is a very important calculation to take into account. At some airports an aircraft can taxi for up to - and over - an hour before take-off. This may be the case at busier airports at peak times, for example, JFK airport in New York. This would mean adding extra fuel to cater for your journey to the runway and once you’re there, you could be caught in a queue of other aircraft waiting to take-off. Jet engines can use quite a bit of fuel even when idle so whether waiting at the runway or if weather factors are keeping you stationary, such as de-icing, this fuel has to be accounted for.
3. Route to destination
Sometimes an airline will have a standard route it uses for a flight, and this will be saved in a database on the Flight Guidance Computer on the aircraft. Although the standard distance doesn’t usually change, with every flight the time to fly the same route (and therefore the fuel required) could alter, for example it would take longer if you are flying in strong head winds.
You can’t just fly any route you fancy! Carriers need permission to fly through the airspace of each country they pass over. If for any reason you don’t have permission, the route will be altered.
If there are strong winds at play, or a jet stream (a narrow corridor of strong wind) the flight route may be altered to give the best tail wind, which will shorten flight times to save fuel. Thanks to modern technological advancements aircraft fly just 1000ft apart vertically. This is called Reduced Vertical Seperation Minima (RVSM). This usually starts from 29,000ft, to fly in this airspace you will have to have certain equipment on board, an autopilot for example. If you are planning to fly on a track from 0° to 179° you fly at an ‘odd’ flight level i.e. 35,000ft and if your track is from 180° to 359° you fly an ‘even’ flight level at 36,000ft.
5. Set the speed
Flight speeds are usually selected based on the cost index chosen by the airline. It will depend upon whether the aim to to fly fast - this could be if an aircraft is behind schedule and needs to expedite it's return. Alternatively, the aim could be to fly at an economical speed if it is the only flight that aircraft is doing for the day with no time restrictions. The fuel amount required to fly at the planned speed will vary depending on which plan the flight is on.
The lighter the aircraft, the higher it can fly. Some aircraft are restricted by the manufacturer as to how high they can fly. You may plan to fly at a lower altitude if there are stronger tail winds, or ATC may ask you to fly at a certain level to maintain separation from other aircraft. In the flight planning stage, aircraft weight will be estimated depending on factors including cargo, water, catering and extra fuel. This weight will decide the maximum altitude the aircraft can reach. As the aircraft burns fuel it will become lighter and will be able to fly at a higher altitude until it reaches it's ceiling.
7. Alternative airports
In most cases, at least one destination alternative airport has to be factored into the flight plan for use in case the flight must be diverted. Reasons for a diversion can be varied, such as a medical incident, a disruption on board or weather at the destination airport. The fuel required to divert to the alternative airport will be included in the total fuel required.
As you may have noticed, weather underpins almost every aspect of a planning a flight; from what runway is used for departure, to whether you can actually land at your destination due to the forecast. You may have to go off your planned route to avoid big storms, so this is something pilots take into consideration when planning how much fuel they require. This fuel will be added at the commanders discretion and would count as "Extra Fuel".
Fuel has been mentioned repeatedly here, for a very good reason. It is something that is checked, checked again and checked once more by both pilots to make sure they are happy with the amount to be loaded onto the aircraft. The flight plan will have the minimum required to get from A to B, but most pilots will always add more for one or more of the subjects above. Some commercial aircraft can take up to 250 tonnes of fuel!
The fuel required for a flight is made up from the following elements:
Taxi: The fuel required to taxi from stand to the runway holding point.
Trip: The fuel required to take - off at the place of departure and land at the place of arrival.
Contingency: A legal minimum of 5% of trip fuel or 5 minutes (whichever is lower). This is to allow for en-route delays and other unforeseen fuel burn.
Alternate: Fuel from starting a missed approach at destination to landing at the alternate aerodrome.
Final Reserve: A legal minimum required on landing. For a jet aeroplane this is enough to fly for 30 minutes at 1500ft above your alternate aerodrome.
Extra: Extra fuel added at commanders discretion.
So there you have it, an overview of a flight plan in its most basic form shows that two of the biggest factors to consider are the weather, which influences almost every element of the flight and, all things considered, calculating the fuel required, without which you are going nowhere!
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