operator maintenance

contingency maintenance / special maintenance

depot maintenance (beyond O and I level activities, performed in an industrial-type facility) / D-level maintenance

maintenance checks / routine maintenance, scheduled tasks

maintenance idling (periodic running of engine for maintenance purposes)

organizational maintenance (O-level) (day-to-day work that standard airfield maintenance groups perform in support of airfield operations)

routine maintenance / scheduled tasks, maintenance checks

scheduled tasks / routine maintenance, maintenance checks

special maintenance / contingency maintenance

air traffic control operator

control tower operator

early warning system (EWS) operator

identification operator

operator control unit (OCU)

operator’s pack

operator's permit

ship operator

telephone operator

radio telephone operator (RTO)

aiming rule operator

azimuth (deflection) display board operator

control post operator

vertical control operator

fire-control operator

navigator-radio operator

air operator certificate

aircraft operator

airport operator

flight operator

flight radio operator

flight systems operator

operator  D / Dt

operator communication