Definition
A regulatory threshold of accumulated flight-time hours that triggers a required inspection on aircraft used for hire or for flight instruction provided for hire. Under 14 CFR 91.409, an aircraft operated in these capacities must receive a 100-hour inspection before further flight once it has been operated for 100 hours since its last such inspection. The 100 hours may be exceeded by up to 10 hours, but only when necessary to fly the aircraft to a place where the inspection can be performed, and the excess time must be subtracted from the next 100-hour interval.
Plain English
When an aircraft is rented out with an instructor or used to carry people for hire, it must be inspected every time it has flown 100 hours. You can go up to 10 hours over only to reposition the aircraft for the inspection, and those extra hours come off the next 100-hour cycle.
Context Anchor
Seen in aircraft inspection requirements, maintenance records, and rental or flight school aircraft scheduling.
Why Pilots Care
Compliance prevents legal operation violations and helps maintain aircraft safety by identifying wear or issues that develop with use.
Intuition Check
Do not read this as 100 hours on a clock after the last inspection. It means 100 hours of counted aircraft operation, not four calendar days or 100 hours sitting parked.
Example Sentence 1
The flight school grounded the trainer because it had reached 100 hours of operation since its last inspection.
Example Sentence 2
Before scheduling a cross-country training flight, the instructor verified that the aircraft had not exceeded its 100 hours of operation limit.