Definition
A required inspection interval for aircraft used to carry persons (other than crewmembers) for hire, or for flight instruction for hire. The aircraft must be inspected every 100 hours of time-in-service, and may not be operated beyond that interval unless the inspection has been completed. The inspection may be exceeded by up to 10 hours only when necessary to reach a place where the inspection can be performed, and the excess time must then be subtracted from the next 100-hour interval.
Plain English
If an aircraft is used for paid passenger flights or paid flight training, it has to be checked over by a mechanic every 100 hours of flying time. You can only fly past the 100-hour mark in limited cases (up to 10 extra hours) if you're heading to where the inspection will be done, and that overrun gets deducted from the next cycle.
Context Anchor
Seen in aircraft inspection requirements, rental or training aircraft records, and maintenance logbook discussions.
Why Pilots Care
It is a legal requirement that keeps rental and training aircraft airworthy; skipping it can ground the airplane and create liability for the operator.
Analogy
It is like a service interval on a car, except it is based on aircraft operating hours and can affect whether the aircraft may legally be used for certain flights.
Intuition Check
Do not read “100 hours” as 100 hours on the wall clock or 100 hours since last Tuesday. In this context, it means 100 hours of aircraft operating time counted for inspection purposes.
Example Sentence 1
The flight school grounded the trainer until the 100-hour inspection was signed off in the maintenance logbook.
Example Sentence 2
After logging 100 hours, the instructor scheduled the required inspection to keep the aircraft legal for student training.