Mass and Balance Terminology: BEM, DOM, ZFM, TOM, and Fuel Definitions

031-02-01Pablo Asensio Martínez2026-04-012 min

Standard Mass Definitions

  • Basic Empty Mass (BEM): The mass of the aeroplane including:

    • Airframe, engines, and all fixed equipment.
    • Unusable fuel and oil.
    • Hydraulic fluid, fire extinguishers, emergency oxygen, etc.
    • Does not include crew or usable fuel.

  • Dry Operating Mass (DOM): The total mass of the aeroplane ready for a specific type of operation, excluding usable fuel and traffic load.

    • DOM = BEM + Crew + Crew Baggage + Catering + Potable Water + Lavatory Chemicals.

  • Operating Mass (OM): The DOM plus fuel but without traffic load.

    • OM = DOM + Fuel Load.

  • Zero Fuel Mass (ZFM): The total mass of the aeroplane including everything except usable fuel.

    • ZFM = DOM + Traffic Load.

Load Definitions

  • Useful Load: The total mass of the items that can be carried in addition to the Basic Empty Mass.

    • Useful Load = TOM - BEM.
    • Useful Load = Traffic Load + Fuel Load.

  • Traffic Load (Payload): The total mass of passengers, baggage, and cargo, including any non-revenue load.

    • Traffic Load = TOM - DOM - Fuel Load.

  • Fuel Load: The total mass of usable fuel on board.

    • Block Fuel (Ramp Fuel): The total fuel on board before starting engines.
    • Taxi Fuel: Fuel consumed during ground operations before take-off.
    • Take-off Fuel: Fuel on board at the start of the take-off run (Block Fuel - Taxi Fuel).
    • Trip Fuel: Fuel required for the flight from take-off to landing.
    • Landing Fuel: Fuel remaining on board at landing (Take-off Fuel - Trip Fuel).

Relationship Summary

$ \text{DOM} = \text{BEM} + \text{Crew} + \text{Pantry} $ $ \text{ZFM} = \text{DOM} + \text{Traffic Load} $ $ \text{TOM} = \text{ZFM} + \text{Take-off Fuel} $ $ \text{LM} = \text{TOM} - \text{Trip Fuel} $