Maximum Take-Off Weight
Encyclopedia
The Maximum Takeoff Weight (MTOW) 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, due to structural or other limits. The analogous term for rockets is Gross Lift-Off Mass, or GLOW. MTOW is usually specified in units of kilogram
s or pounds
, but some aircraft manufacturers also use kilogram-force
(kgf) or pound-force
(lbF).
MTOW is the heaviest weight at which the aircraft has been shown to meet all the airworthiness
requirements applicable to it. MTOW of an aircraft is fixed, and does not vary with altitude or air temperature or the length of the runway to be used for takeoff or landing. A different weight the "maximum permissible takeoff weight", or "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 MTOW.
At the MTOW, all aircraft of a type and model must be capable of complying with all these certification requirements.
In many examples, such as the Cessna 208 Caravan, the increased MTOW option generally consists of a reinforced undercarriage. There are other aircraft such as the Cessna 206 which offers a Heavy Undercarriage option at time of purchase, but comes with no such increase in MTOW.
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.
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
is the maximum weight at which the pilot of the aircraft is allowed to attempt to take off, due to structural or other limits. The analogous term for rockets is Gross Lift-Off Mass, or GLOW. MTOW is usually specified in units of kilogram
Kilogram
The kilogram or kilogramme , also known as the kilo, is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype Kilogram , which is almost exactly equal to the mass of one liter of water...
s or pounds
Pound (mass)
The pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
, but some aircraft manufacturers also use kilogram-force
Kilogram-force
A kilogram-force , or kilopond , is a gravitational metric unit of force. It is equal to the magnitude of the force exerted by one kilogram of mass in a gravitational field...
(kgf) or pound-force
Pound-force
The pound force is a unit of force in some systems of measurement including English engineering units and British gravitational units.- Definitions :...
(lbF).
MTOW is the heaviest weight at which the aircraft has been shown to meet all the airworthiness
Airworthiness
Airworthiness is a term used to describe whether an aircraft has been certified as suitable for safe flight. Certification is initially conferred by a Certificate of Airworthiness from a National Airworthiness Authority, and is maintained by performing required maintenance actions by a licensed...
requirements applicable to it. MTOW of an aircraft is fixed, and does not vary with altitude or air temperature or the length of the runway to be used for takeoff or landing. A different weight the "maximum permissible takeoff weight", or "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 MTOW.
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 MTOW, all aircraft of a type and model must be capable of complying with all these certification requirements.
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 (Landing and air traffic control fees being MTOW based ).In many examples, such as the Cessna 208 Caravan, the increased MTOW option generally consists of a reinforced undercarriage. There are other aircraft such as the Cessna 206 which offers a Heavy Undercarriage option at time of purchase, but comes with no such increase in MTOW.
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 flapFlap (aircraft)Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
setting. See the Spanair Flight 5022Spanair Flight 5022Spanair Flight JK 5022, from Barajas Airport in Madrid to Gran Canaria Airport in Gran Canaria, Spain, crashed just after take off from runway 36L of Barajas Airport at 14:24 CEST on 20 August 2008. The aircraft was a McDonnell Douglas MD-82, registration EC-HFP... - 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 DisasterMunich air disasterThe Munich air disaster occurred on 6 February 1958, when British European Airways Flight 609 crashed on its third attempt to take off from a slush-covered runway at Munich-Riem Airport in Munich, West Germany. On board the plane was the Manchester United football team, nicknamed the "Busby Babes",...
- 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.
See also
- Maximum Zero Fuel WeightMaximum Zero-Fuel WeightThe Zero Fuel Weight of an airplane is the total weight of the airplane and all its contents, minus the total weight of the fuel on board....
- Operating Empty Weight
- List of airliners by Maximum Takeoff Weight
- Aircraft Gross WeightAircraft gross weightThe aircraft gross weight is the total aircraft weight at any moment during the flight or ground operation.The aircraft gross weight decreases during flight due to fuel and oil consumption...