Definition
The maximum allowable weight of an aircraft, including everything aboard except usable fuel — that is, the airframe, all installed equipment, crew, passengers, baggage, and cargo. It is a structural limit set by the manufacturer (defined under General Aviation Manufacturers Association standards) to control bending loads on the wing root, since fuel carried in the wings helps relieve those loads in flight.
Plain English
The heaviest the aircraft is allowed to be before any usable fuel is added. Anything above this weight has to come from fuel in the wings, not from more people or cargo.
Context Anchor
Seen in weight-and-balance data, loading charts, and the aircraft flight manual or pilot’s operating handbook.
Derivation
Zero fuel' literally describes the condition: the aircraft weighed as if it had no usable fuel on board. GAMA stands for the General Aviation Manufacturers Association, the industry group that standardized this and other weight definitions so different manufacturers use the same terms.
Why Pilots Care
Exceeding this limit can overstress the wing structure even if total gross weight is within limits.
Grounding Statement
Check this limit by adding the airplane, people, baggage, and cargo first, before counting usable fuel.
Intuition Check
“Zero fuel” does not mean the airplane has no fuel on board. It means usable fuel is left out of this particular weight calculation.
Example Sentence 1
After loading the passengers and bags, the captain checked that the aircraft was still below maximum zero fuel weight before adding fuel for the trip.
Example Sentence 2
During preflight, the operator verified the baggage and passenger load against the aircraft's maximum zero fuel weight.