Maximum Permissible Takeoff Weight or Maximum Allowed Takeoff Weight
In many circumstances an aircraft may not be permitted to take off at its MTOW. In these circumstances the maximum weight permitted for takeoff will be determined taking account of the following:
- Wing flap setting. See the Spanair Flight 5022
- Airfield altitude (height above sea-level) – This affects air pressure which affects maximum engine power or thrust.
- Air temperature – This affects air density which affects maximum engine power or thrust.
- Length of runway – A short runway means the aircraft has less distance to accelerate to takeoff speed. The length for computation of maximum permitted takeoff weight may be adjusted if the runway has clearways and/or stopways.
- Runway wind component – The best condition is a strong headwind straight along the runway. The worst condition is a tailwind. If there is a crosswind it is the wind component along the runway which must be taken into account.
- Condition of runway – The best runway for taking off is a dry, paved runway. An unpaved runway or one with traces of snow will provide more rolling friction which will cause the airplane to accelerate more slowly. See the Munich Air Disaster
- Obstacles – An airplane must be able to take off and gain enough height to clear all obstacles and terrain beyond the end of the runway.
The maximum weight at which a takeoff may be attempted, taking into account the above factors, is called the maximum permissible takeoff weight, maximum allowed takeoff weight or regulated takeoff weight.
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