Definition
With respect to maintenance time records, the time from the moment an aircraft leaves the surface of the earth until it touches down at the next point of landing.
Plain English
The total time the aircraft is actually airborne, measured from lift-off to touchdown. Time spent taxiing, running the engine on the ground, or sitting at the gate does not count.
Context Anchor
Seen in aircraft maintenance records and 100-hour inspection requirements.
Derivation
The phrase sounds like it should mean any time the aircraft is being used, but in FAA regulations it has a narrower meaning: only the time the aircraft is in service in the air.
Why Pilots Care
Determines when required inspections become due based on actual usage rather than elapsed calendar days.
Intuition Check
Do not assume time in service means all time the engine is running, all time on the rental schedule, or all time since the last inspection. For this maintenance rule, it means flight time from liftoff to landing.
Example Sentence 1
The mechanic logged 1.2 hours of time in service for the cross-country flight, even though the engine ran for nearly two hours including taxi and runup.
Example Sentence 2
The mechanic updated the logbook with the flight's time in service using the tachometer reading.