Maximum takeoff weight

The Maximum Takeoff Weight or Maximum Takeoff Mass of an aircraft is the maximum weight at which the pilot of the aircraft is allowed to attempt to take off. The Maximum Takeoff Weight is the heaviest weight at which the aircraft has been shown to meet all the airworthiness requirements applicable to it. The airworthiness requirements include many related to strength of the structure, and performance. At its Maximum Takeoff Weight an aircraft complies with all the structural and performance requirements applicable to aircraft in its class.

The Maximum Takeoff Weight of an aircraft is fixed. It does not vary with altitude or air temperature or the length of the runway to be used for takeoff or landing. (A different weight, called the maximum permissible takeoff weight, or the regulated takeoff weight, varies according to flap setting, altitude, air temperature, length of runway and other factors. It is different from one takeoff to the next, but can never be higher than the Maximum Takeoff Weight.)

Maximum Takeoff Weight is usually specified in units of kilograms or pounds.

Certification standards

Certification standards applicable to the airworthiness of an aircraft contain many requirements. Some of these requirements can only be met by specifying a maximum weight for the aircraft, and demonstrating that the aircraft can meet the requirement at all weights up to, and including, the specified maximum. These requirements include:

• structural requirements - to ensure the aircraft structure is capable of withstanding all the loads likely to be imposed on it during maneuvering by the pilot, and gusts experienced in turbulent atmospheric conditions.
  
• performance requirements - to ensure the aircraft is capable of climbing at an adequate gradient with all its engines operating; and also with one engine inoperative.
  

At the Maximum Takeoff Weight, all aircraft of a type and model must be capable of complying with all these certification requirements.

For example, consider a wide-body civil airliner designed and manufactured in the USA. Large civil airliners in the USA require airworthiness certificates in the transport category. The airworthiness requirements for airplanes in the transport category are specified in Part 25 of the US Federal Aviation Regulations. Part 25 is titled Airworthiness Standards: Transport Category Airplanes. The Maximum Takeoff Weight of a transport category airplane is the maximum weight at which the airplane has been demonstrated to comply with all the requirements specified in Part 25 of the FAR.

Maximum permissible takeoff weight

In many circumstances an aircraft may not be permitted to takeoff at its Maximum Takeoff Weight. In these circumstances the maximum weight permitted for takeoff will be determined taking account of the following:

• Wing flap setting.
  
• 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.
  
• 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, or the regulated takeoff weight. Neither of these names is defined in aviation standards so the names are informal, and there are other names too.

Multiple MTOW

Among large airliners the same model of aircraft can have more than one MTOW. An airline can choose to have its airliner certified for an increased weight at an additional cost. Some airlines which do not require a high MTOW choose to have a lower MTOW for that particular aircraft to reduce costs.

See Also

• Maximum Zero Fuel Weight
• List of airliners by Maximum Takeoff Weight