100-Hour Inspection Requirements for Aircraft

Aircraft used to carry passengers for hire, or rented out for flight instruction where the instructor also provides the airplane, must be inspected within the preceding 100 hours of time in service before further such flights. That is the core of the 100-hour inspection requirements for aircraft under 14 CFR 91.409(b), and it sits on top of the annual inspection every civil aircraft already needs.¹ The rule is short. The details around who can sign it, how the hours are counted, and what happens if you overshoot are where operators get into trouble.

Which Aircraft Are Covered

Two use cases pull an airplane into the 100-hour rule. The first is carrying a person other than a crewmember for hire: air taxi work, sightseeing, and similar revenue flights with paying passengers. The second, and the one most pilots encounter, is paid flight instruction in which the instructor supplies the airplane. Rent a trainer from a flight school and take a lesson from an instructor working for that school, and the airplane needs 100-hour inspections. Own the airplane yourself and hire a freelance instructor to sit in the right seat, and it does not.¹

Purely private operations are exempt. If the airplane is flown only for personal travel and never carries paying passengers or is offered for instruction, the annual inspection every 12 calendar months is the only recurring inspection required. The trigger is how the aircraft is used, not how it is registered or insured.

How the 100-Hour Differs From the Annual

The physical work is identical. Both inspections follow the same checklist in 14 CFR Part 43, Appendix D, and both require the same access, disassembly, and scrutiny. The differences are administrative.

An annual satisfies the 100-hour requirement, but a 100-hour does not satisfy the annual. If a mechanic holding Inspection Authorization performs the work and enters it as an annual, both clocks reset. A 100-hour signed off by an A&P without IA resets only the 100-hour clock.¹ For a busy flight school airplane that hits 100 hours in six weeks, that flexibility matters: the annual can stay on its own schedule while an ordinary A&P handles the recurring 100-hours.

Who Can Perform the Inspection

A certificated mechanic with an airframe rating can inspect the airframe and its related parts and approve the aircraft for return to service. A powerplant rating gives the same authority over the engine, propeller, and their components.²³ Most 100-hour inspections are done by mechanics holding both, commonly called A&Ps.

No Inspection Authorization is needed. IA is required for annuals and for progressive inspections, not for the 100-hour. Certificated repair stations and the aircraft manufacturer can also perform the inspection. One catch: a person working under the supervision of a certificated mechanic cannot perform Part 91 inspections, even though supervised maintenance in general is allowed.⁴

How the 100 Hours Is Counted

The clock runs on time in service, which the FAA defines as the time from the moment an aircraft leaves the surface of the earth until it touches down at the next point of landing.⁵ Flight time only. Taxi, run-ups, and sitting on the ramp with the engine running do not count.

This matters because the numbers on your instruments usually are not time in service. A Hobbs meter typically starts when the engine runs or when electrical power is on, and it accumulates faster than actual flight time. A tachometer-based hour meter runs on a different scale still. For compliance, the operator has to track the figure that matches the FAA’s definition, not whatever the panel meter happens to show.

What the Inspection Covers

Appendix D to Part 43 sets the scope. Before anything else, the mechanic removes inspection plates, access panels, fairings, and cowlings, then cleans the aircraft so the underlying structure is visible.⁶ From there the inspection works through defined groups:

Cabin and cockpit: seats, safety belts, windows, instruments, controls, battery, general systems.
Engine and nacelle: leak checks, cylinder compression, screens and sump drain plugs for metal, mount integrity, exhaust, accessory security.
Landing gear: shock struts, tires, brakes, wheel bearings, retraction mechanism, hydraulic lines.
Wing and center section: skin condition, distortion, evidence of structural failure, attachment security.
Empennage: tail assembly fabric or skin, distortion, structural condition, control surface operation.

Appendix D uses the phrase “as applicable to the particular aircraft.” The mechanic tailors the work to the specific make and model, so a retractable-gear Cessna gets retraction checks that a fixed-gear trainer does not.

Records the Inspection Produces

Before starting, the mechanic reviews the aircraft’s maintenance records, which the owner is required to keep showing airworthiness directive status, life-limited parts for the airframe, engine, and propeller, and prior maintenance and inspection entries.⁷

After the inspection, the mechanic enters the type of inspection performed, the date, the aircraft’s total time in service, and their signature with certificate number and certificate type.⁸ If the aircraft passes, the entry includes a certification approving it for return to service. Without that entry and signature, the inspection is not legally complete no matter how thorough the physical work was.

When the Aircraft Fails

If defects make the aircraft unairworthy or out of compliance with its type certificate or an airworthiness directive, it cannot be returned to service until those items are fixed. The mechanic must give the owner a signed, dated list of every discrepancy and unairworthy item, and the logbook entry certifies that the inspection was performed and that this list was provided, along with the date of the list.⁸ The airplane stays grounded until each item is addressed and it is approved for return to service. Items permitted to be inoperative under the aircraft’s minimum equipment provisions get an “Inoperative” placard on the affected instrument or control and stay on the discrepancy list.

The 10-Hour Ferry Allowance

If the aircraft reaches 100 hours away from a maintenance facility, up to 10 additional hours are allowed to fly it to a place where the inspection can be done.¹ This is a ferry allowance only. It cannot be used for revenue flights or instruction on the way to the shop.

The overage also shortens the next cycle. Fly 7 hours past the 100-hour mark to reach the mechanic, and the next 100-hour comes due at 193 hours total time, not 207. Time used in the grace period is deducted from the following interval, so there is no way to routinely push into it without giving the hours back.

Progressive Inspection as an Alternative

Operators who find the 100-hour cycle disruptive can apply for a progressive inspection program, which spreads the same work across shorter, more frequent visits. The owner submits a written request to the local Flight Standards office and must have a mechanic with Inspection Authorization, a certificated repair station, or the aircraft manufacturer supervise the program.¹ The application requires a detailed procedures manual with inspection intervals, sample forms, and recordkeeping instructions, and the program must inspect the entire aircraft within every 12 calendar months. Progressive programs suit high-utilization aircraft like school trainers, but they add administrative work and coordination with the supervising inspector. If the owner discontinues the program, they must notify Flight Standards in writing immediately.

Penalties for Flying Past Due

Operating an aircraft beyond its 100-hour inspection, without the ferry allowance, is classified as a Severity 2 violation under FAA enforcement guidance.⁹ The consequences vary by who is cited:

Certificate action: an individual certificate holder faces a suspension of 60 to 120 days.
Civil penalties for individuals and small businesses: sanction guidance in the enforcement order sets fines of $400 to $700 per violation. The statutory maximum civil penalty for an airman serving as an airman is $1,875 per violation as of the most recent inflation adjustment.¹⁰
Civil penalties for larger operators: businesses that do not qualify as small can face up to $75,000 per violation.

The FAA sets the actual sanction within these ranges based on compliance history, the hazard the violation created, and whether the operator took prompt corrective action. A suspension also grounds the certificate holder for its full duration, which can be severe for a commercial operation.

Typical Costs

Costs vary with the aircraft, the shop, and what the mechanic finds. Labor rates at maintenance facilities commonly run $100 to $150 per hour for piston aircraft. A simple two-seat trainer might take 10 to 12 hours; a more complex single with a constant-speed propeller and retractable gear can take 18 to 22. That puts labor alone at roughly $1,000 to $3,300 before parts, oil, filters, or repairs.

Unexpected findings drive the real bill. A weak cylinder on a compression check, or metal in an oil analysis, can turn a routine inspection into a major expense. Operators of for-hire aircraft should budget for some level of unscheduled maintenance at each 100-hour interval rather than treating the inspection labor as the total cost.

1
eCFR. 14 CFR 91.409 – Inspections
2
eCFR. 14 CFR 65.85 – Airframe Rating Additional Privileges
3
eCFR. 14 CFR Part 65 Subpart D – Mechanics
4
eCFR. 14 CFR 43.3 – Persons Authorized To Perform Maintenance, Preventive Maintenance, Rebuilding, and Alteration
5
eCFR. 14 CFR 1.1 – General Definitions
6
eCFR. 14 CFR Part 43 Appendix D – Scope and Detail of Items To Be Included in Annual and 100-Hour Inspections
7
eCFR. 14 CFR 91.417 – Maintenance Records
8
eCFR. 14 CFR 43.11 – Content, Form, and Disposition of Records for Inspections
9
Federal Aviation Administration. FAA Order 2150.3C – FAA Compliance and Enforcement Program
10
Federal Register. Revisions to Civil Penalty Amounts, 2025