The Annual Inspection: 91.409(a)
FAR 91.409(a) prohibits operating an aircraft unless it has received an inspection in accordance with Part 43 within the preceding 12 calendar months and received an airworthiness approval. That phrasing matters. "12 calendar months" is not 365 days — it means through the end of the same calendar month one year later. An annual completed on March 10 is valid through March 31 of the following year, giving the owner up to roughly 13 months if the inspection was done early in the month. This is a classic oral question because many applicants conflate calendar months with a fixed day-count.
The annual must be performed by an A&P mechanic holding an Inspection Authorization (IA), or by a certificated repair station, or the aircraft manufacturer under specific conditions. Signing off an annual without an IA is a common trap question — a standard A&P cannot do it.
An aircraft under an approved progressive inspection program per 91.409(d) is exempt from the annual requirement, provided the program keeps all systems current on a rolling basis approved by the local FSDO.
The 100-Hour Rule: 91.409(b)
The 100-hour inspection applies under one specific condition: the aircraft is being used to carry persons for hire, or to give flight instruction for hire. Flight schools and charter operators running under Part 91 are the primary audience. If neither of those conditions applies, there is no 100-hour requirement — the annual alone suffices.
The 100-hour interval is measured in hours of time in service, not calendar time. An aircraft at 99.7 hours can fly another 0.3 hours before the inspection is required. It cannot legally depart on a 1.5-hour flight at 99.7 hours without first getting the inspection, unless the overrun provision applies.
91.409(b) permits exceeding the 100-hour limit by up to 10 hours — but only to ferry the aircraft to a maintenance facility. Those excess hours are not "free." They are deducted from the next 100-hour interval. If you fly 7 hours over to reach your IA, your next inspection is due at 93 hours of service, not 100. An annual inspection performed at the proper interval satisfies the 100-hour requirement, but a 100-hour inspection does not substitute for an annual.
Approved Inspection Programs for Turbine and Large Aircraft
91.409(e) creates a different framework for large airplanes, turbojets, turbopropeller-powered multiengine airplanes, and large rotorcraft. These aircraft must be maintained under an inspection program selected under 91.409(f), which allows operators to use:
- A continuous airworthiness inspection program (CAIP) currently in use by a Part 121 or 135 operator
- An approved aircraft inspection program (AAIP) under Part 135.419
- A program recommended by the manufacturer
- An FAA-approved program established per 91.409(f)(4)
This is the regulatory foundation for the Continuous Airworthiness Maintenance Programs (CAMP) that airline and fractional operators use. Rather than discrete annual or 100-hour events, these programs track components, zones, and systems on task-card cycles derived from the manufacturer's Maintenance Review Board (MRB) report. Understanding how CAMP intersects with Part 91 authority is directly relevant to pilots preparing for cargo carrier or fractional ownership technical interviews, where evaluators expect more than a surface-level answer on maintenance authority.
What This Means in an Interview
Interviewers at major and regional carriers use 91.409 to probe two things: whether you understand the regulatory logic behind maintenance requirements, and whether you can distinguish between the annual, the 100-hour, and approved programs without conflating them. Weak answers give the rule. Strong answers explain the conditions under which each applies, the overrun nuance, and why turbine-class aircraft operate under a fundamentally different framework.
Real-world gouge from recent technical interviews shows that evaluators often follow up with ADs — specifically 91.409's relationship to 91.403 and operator maintenance responsibility. Knowing that 91.409 sets inspection intervals while 91.403 assigns airworthiness responsibility to the owner/operator is the kind of distinction that separates prepared candidates from those who memorized bullet points.
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