AV1ATES: The Required Aircraft Inspections Explained

AV1ATES is a memory aid for the recurring inspections and checks that make an airplane legal to fly: Airworthiness Directives, VOR check, 100-hour inspection, Annual inspection, Transponder check, ELT inspection, and Static system and altimeter check. Each comes from 14 CFR part 91 or part 39, and not every item applies to every flight: the 100-hour applies only when carrying people for hire or giving flight instruction for hire in an airplane the instructor provides, and the VOR and static system checks are required only for IFR.

AV1ATES at a glance

How calendar months, days and hours work

In the words of the FAA’s Pilot’s Handbook of Aeronautical Knowledge (PHAK), a period of 12 calendar months extends from any day of a month to the last day of the same month the following year, so an annual signed off on March 6 is good through March 31 of the next year. The VOR check counts days, and the 100-hour counts hours of time in service, which 14 CFR 1.1 defines as liftoff to touchdown at the next landing.

A: Airworthiness Directives

ADs are legally enforceable rules that apply to aircraft, engines, propellers and appliances (14 CFR 39.3), and anyone who operates a product that does not meet an applicable AD is in violation (39.7). Some require one-time action, others recur, and emergency ADs can require action before further flight. The records must show each applicable AD’s status, method of compliance, number and revision date and, if it recurs, when the next action is due (91.417(a)(2)(v)). Examiners like two points: there is no overfly allowance on an AD’s hour limit unless the AD provides one, and a Special Airworthiness Information Bulletin (SAIB) is advisory, not mandatory. ADs are published in the FAA’s Dynamic Regulatory System.

V: VOR check (IFR only)

Under 14 CFR 91.171, you may not fly IFR using VOR navigation unless the equipment is maintained under an approved procedure or has been operationally checked within the preceding 30 days and found within these limits:

• VOT or repair station test signal at the departure airport: plus or minus 4 degrees. With a VOT and the needle centered, the OBS reads 0 FROM or 180 TO (AIM 1-1-4).
• Ground checkpoint on the airport surface: plus or minus 4 degrees.
• Airborne checkpoint if neither of those is available, or failing that a prominent ground point on a VOR airway, preferably more than 20 nautical miles from the VOR: plus or minus 6 degrees.
• Dual VOR check: two independent receivers tuned to the same VOR must agree within 4 degrees.

Whoever does the check enters the date, place and bearing error and signs the aircraft log or other record (91.171(d)). Checkpoints and VOTs are listed in the Chart Supplement. VFR flights need no VOR check, but expect the question anyway, and again in instrument training.

1: the 100-hour inspection

14 CFR 91.409(b) requires an annual or 100-hour inspection within the preceding 100 hours of time in service when an aircraft carries any person other than a crewmember for hire, or when someone gives flight instruction for hire in an aircraft that person provides. A flight school airplane used for the school’s lessons needs one; your own airplane with an instructor you hire does not (it still needs its annual).

• The 10-hour allowance: the limit may be exceeded by no more than 10 hours, only while en route to a place where the inspection can be done, and the excess counts toward the next 100 hours.
• An annual counts as a 100-hour, but a 100-hour counts as an annual only if performed by a person authorized to do annuals and entered as an annual (91.409(a)).
• Who does it: a mechanic with airframe and powerplant ratings (14 CFR 65.85 and 65.87), an appropriately rated repair station, or the manufacturer.

A: the annual inspection

Under 14 CFR 91.409(a), no one may operate an aircraft unless it has had an annual inspection within the preceding 12 calendar months, approved for return to service by a person authorized under 14 CFR 43.7: per the PHAK, a mechanic holding an Inspection Authorization (IA), the manufacturer, or an appropriately rated repair station. If it lapses, the airplane may fly only under a special flight permit to a place where the inspection can be done (14 CFR 21.197), and the PHAK adds that applicable ADs that are due must be complied with first. The exceptions in 91.409(c) include progressive inspection programs and experimental, light-sport category and provisional certificates.

T: transponder check

14 CFR 91.413 says no person may use an ATC transponder unless, within the preceding 24 calendar months, it has been tested and inspected to part 43, appendix F, by an appropriately rated repair station or another person listed in 91.413(c). It is not IFR-only: it applies whenever you use the transponder, VFR included. Where 14 CFR 91.215 requires a transponder is covered in our airspace classes guide.

E: the ELT

Most U.S.-registered civil airplanes must have an approved, operable emergency locator transmitter attached (14 CFR 91.207(a)). It must be inspected within 12 calendar months after the last inspection for proper installation, battery corrosion, operation of the controls and crash sensor, and a sufficient signal radiated from its antenna (91.207(d)). The battery must be replaced or recharged after more than 1 cumulative hour of transmitter use, or when 50 percent of its useful life has expired, with the new date marked on the outside of the transmitter and entered in the maintenance record (91.207(c)). Paragraph (f) lists exceptions, such as training operations conducted entirely within a 50 nautical mile radius of the airport where they began, or an ELT removed for repair for up to 90 days with a records entry and an “ELT not installed” placard. A good habit from AIM 6-2-4: monitor 121.5 MHz before engine shutdown to catch an accidental activation.

S: static system and altimeter

To fly IFR in controlled airspace, 14 CFR 91.411 requires that within the preceding 24 calendar months each static pressure system, each altimeter instrument and each automatic pressure altitude reporting system (the encoder that sends altitude to the transponder) has been tested and inspected to part 43, appendices E and F. The static system must also be retested after it has been opened and closed, except for use of the system drain and alternate static valves. Our pitot-static system guide explains the system.

Worked example: is this airplane legal today?

Suppose today is October 8, 2026, and you are about to fly a VFR dual lesson, using the transponder, in a flight school airplane. The school provides the airplane and the instructor, so the 100-hour applies. Time in service now reads 4,798.9 hours:

The verdict: legal for today’s VFR lesson, but not for an IFR flight using VOR navigation until someone performs and logs a VOR check. The annual and ELT inspection are due by October 31, and a 1.5-hour lesson leaves 11.9 hours before the 100-hour. The 10-hour allowance would not help at 4,812.3, because the recurring AD comes due at the same time with no allowance of its own. Change one date and the answer flips: an annual signed off September 21, 2025 would have expired at the end of September 30, 2026.

Study gear for the airworthiness questions

What you'll need

The references students use to master airworthiness for the oral exam, plus a kneeboard for the airplane.

ASA FAR/AIM

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FAA-S-ACS-6C Private Pilot Airplane ACS

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ASA Private Pilot Oral Exam Guide

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Battleboard Kneeboard Tech Edition

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How AV1ATES shows up on the checkride

In the Private Pilot ACS (FAA-S-ACS-6C), Task I.B, Airworthiness Requirements, covers required inspections and logbook documentation (PA.I.B.K1b), ADs and SAIBs (PA.I.B.K1c), special flight permits (PA.I.B.K1d), and owner, operator and pilot in command responsibilities (PA.I.B.K1e). Know the split: the owner or operator is primarily responsible for maintaining airworthiness (91.403(a)), and the pilot in command determines whether the airplane is in condition for safe flight (91.7(b)). The skill element is to determine that the airplane is airworthy in a scenario the evaluator gives you (PA.I.B.S2), just like the example above. See our oral exam and checkride guides, and NWKRAFT for the preflight briefing.

Frequently asked questions

What does AV1ATES stand for?

AV1ATES stands for Airworthiness Directives, VOR check, 100-hour inspection, Annual inspection, Transponder check, ELT inspection, and Static system and altimeter check. The 1 stands for the 100-hour inspection.

When is a 100-hour inspection required?

Under 14 CFR 91.409(b), when an aircraft carries any person other than a crewmember for hire, or when someone gives flight instruction for hire in an aircraft that person provides. An annual also satisfies it.

When is an annual inspection due?

Within 12 calendar months, which run to the last day of the month. An annual signed off on March 6 is good through March 31 of the following year.

Is a VOR check required for VFR flight?

No. The 30-day VOR check in 14 CFR 91.171 applies only to IFR operations that use the VOR system of radio navigation.

How often must the ELT be inspected?

Within 12 calendar months after the last inspection, under 14 CFR 91.207(d). Its battery must be replaced or recharged after more than 1 cumulative hour of use or when 50 percent of its useful life has expired.

Can a 100-hour inspection be overflown?

By no more than 10 hours, and only while en route to a place where the inspection can be done. The excess counts toward the next 100 hours, and AD limits have no such allowance unless the AD provides one.

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