Definition
The greatest total mass of an aircraft, including the airframe, fuel, oil, crew, passengers, baggage, and cargo, at which the aircraft is certificated to begin the takeoff run. Operating at any mass above this limit is prohibited.
Plain English
The heaviest the aircraft is allowed to be at the moment it starts its takeoff roll. Anything heavier than this is not permitted.
Context Anchor
Seen in aircraft limitations, loading calculations, and takeoff performance planning before flight.
Derivation
The word 'mass' is used here rather than 'weight' because mass is the amount of matter in the aircraft and does not change with location, while weight changes with gravity. International (ICAO) certification standards prefer 'mass' for this reason. In U.S. practice the equivalent term is Maximum Takeoff Weight.
Why Pilots Care
Exceeding this mass can result in insufficient runway length, reduced climb performance, or structural damage.
Intuition Check
Maximum does not mean a target or recommended loading; it means a limit that must not be exceeded. Takeoff mass is not empty aircraft mass; it includes fuel, people, baggage, cargo, and anything else on board for takeoff.
Example Sentence 1
After loading the passengers and baggage, the pilot calculated the total weight and confirmed it was below the Maximum Takeoff Mass listed in the POH.
Example Sentence 2
The certification documents specify the maximum takeoff mass for both standard and high-altitude operations.