The 100-Hour Inspection Rule (14 CFR § 91.409), Explained

If you operate an aircraft for hire — rental, or flight instruction for hire — you've run into the 100-hour inspection requirement. It's one of the most common maintenance-compliance questions in general aviation, and it trips people up in a few predictable ways.

The Basic Rule

Under 14 CFR § 91.409, an aircraft used to carry persons for hire, or used for flight instruction for hire, must receive an inspection every 100 hours of time in service, performed by a person authorized to perform annual inspections. This is separate from the annual inspection every aircraft needs regardless of use.

The 10-Hour Overage Allowance

The rule allows the 100-hour inspection to be exceeded by up to 10 hours if necessary to reach a location where the inspection can be performed — but that overage is then deducted from the next 100-hour interval. It's a narrow allowance for reaching a mechanic, not a grace period to keep flying on schedule.

Where It Doesn't Apply

The 100-hour requirement doesn't apply to aircraft operated under a progressive inspection program, and it doesn't apply the same way if the aircraft is leased to a school and not otherwise used for compensation or hire beyond that instruction — the details of "for hire" status matter, so if your operation is structured unusually, that's worth confirming with your mechanic or an aviation attorney rather than assuming.

Why This Is Easy to Miss

The 100-hour count resets based on Hobbs or tach time in service, not calendar time, which means an aircraft that flies a lot can blow past its inspection window in a matter of weeks even if nobody's watching closely. The failure mode is almost always the same: nobody was tracking hours-remaining in real time, so the inspection due date arrived as a surprise instead of a scheduled event.

This is exactly the gap SimpleFBO's maintenance tracking is built to close — every check-in recalculates hours remaining until an aircraft's next 100-hour inspection automatically, and aircraft approaching that window surface on the admin dashboard well before it becomes a problem. See Aircraft Maintenance Tracking for how that works.