Airborne hours
Airborne hours (on the Usage capture screen, the airborne time measure) is the duration the aircraft was off the ground: wheels up to wheels down. Some syndicates bill on airborne time rather than block time because it reflects actual flight time more precisely.
Airborne hours are measured only. When both the takeoff (wheels up) and landing (wheels down) times are recorded on the log, airborne hours are landing − takeoff, floored at zero. When either wheels time is missing, airborne hours are zero (there is no estimate from block time). (Earlier versions fell back to block time − (2 × taxi minutes); that derivation has been removed, and taxi minutes no longer affect any charge.)
Airborne hours are only used for billing when the asset’s billed measure is airborne time. On engine-meter or block-time bases, the wheels times do not affect charges.