Aircraft Inspections, Airworthiness, and Documentation

Why Inspections Matter

An aircraft is only legally airworthy when it meets its type design and is in a condition for safe operation. The 100-hour inspection is one of the primary scheduled maintenance events that keeps general aviation aircraft in that condition. Under 14 CFR Part 91, aircraft operated for hire or flight instruction must receive a 100-hour inspection every 100 hours of flight time. The mechanic who performs and signs off that inspection takes on direct regulatory responsibility for the work. Understanding how to conduct the inspection systematically, classify findings correctly, and document everything completely is a core FAA A&P competency.

Safety Before You Begin

Before touching the aircraft, conduct a proper hazard assessment. Don appropriate PPE: safety glasses, nitrile gloves when handling fluids or cleaning agents, and hearing protection if engines will be run. Chock the wheels and verify the master switch and ignition are off. If any fuel or hydraulic lines will be opened, have absorbent material ready and know the location of the nearest fire extinguisher. Apply a DO NOT OPERATE placard to the cockpit and, where applicable, use lockout/tagout procedures on any circuit breakers or switches that could energize a system you are inspecting. Never assume a system is de-energized — verify it.

The Inspection Checklist and AMM

A 100-hour inspection follows the scope and detail of an annual inspection (14 CFR Part 43 Appendix D lists the minimum areas to examine). In practice, you work from the aircraft manufacturer's Aircraft Maintenance Manual (AMM), which provides model-specific procedures, tolerances, and limits. The school-issued checklist is aligned with the AMM so nothing is skipped. Work through the checklist in sequence — engine compartment, airframe exterior, flight controls, landing gear, interior, instruments, avionics, and required documents. For each line item, record one of three conditions:

• Airworthy — item meets all applicable limits; no action required.
• Repairable — item is outside limits or shows wear but can be corrected before return to service.
• Unairworthy — item is outside limits to a degree that makes flight unsafe; aircraft cannot be returned to service until corrected.

Record actual measurements (wear limits, torque values, gap measurements) wherever the checklist calls for them. A note saying "OK" without data is not acceptable for items that require a measurement.

Using AC 43.13-1B

Advisory Circular 43.13-1B, Acceptable Methods, Techniques, and Practices — Aircraft Inspection and Repair, is your field reference when the AMM does not specify a repair method. It is not mandatory in itself, but methods it describes are FAA-accepted as airworthy practice. When writing corrective actions for discrepancies, cite the specific chapter and section of the AMM or the applicable AC 43.13-1B reference so anyone reading the record knows exactly what authority was used.

Building the Discrepancy List

Every item that is not airworthy at the time of inspection goes on the discrepancy list — a formal document separate from the checklist. Each entry must include:

1. Description of the discrepancy (what, where, measured value vs. limit).

2. Airworthiness classification (repairable or unairworthy).

3. Corrective action planned, with the AMM, AC, or regulatory reference.

4. Priority: unairworthy items go to the top because they prevent return to service.

Organize the list so the supervising A&P and the aircraft owner can see at a glance which items ground the aircraft and which are maintenance items to be corrected before the next flight.

Completing the 14 CFR Part 43 Appendix D Logbook Entry

Part 43 Appendix B specifies what a maintenance record entry must contain, and Appendix D describes the scope of a 100-hour/annual inspection. Your logbook entry for the 100-hour inspection must include:

• Date of inspection completion.
• Aircraft total time in service (hours).
• Name of the person performing the inspection.
• Certificate type and number of the approving mechanic (or IA for annual).
• A description of the work performed — specifically, the statement that the aircraft was inspected in accordance with a 100-hour inspection and found airworthy (or listing items found unairworthy if the aircraft cannot be approved for return to service).
• The aircraft was found to be in airworthy condition, OR a statement that the aircraft was inspected and a list of discrepancies has been provided to the owner.
• Signature and certificate number.

If the aircraft cannot be returned to service, you still sign the logbook but record that a discrepancy list has been furnished to the owner per 14 CFR Part 43. You do not write a return-to-service approval until all unairworthy items are corrected.

Return-to-Service Approval

Once all discrepancies are resolved, the approving A&P (or IA for an annual) makes a return-to-service entry. This entry references the previous inspection entry, lists the corrective actions taken, cites the authority used, and includes the mechanic's signature and certificate number. Incomplete, vague, or missing entries are among the most common FAA compliance findings — precision in paperwork is as important as precision with a torque wrench.

Common Mistakes to Avoid

• Skipping items and marking them airworthy without physically checking them.
• Recording "checked" without measurement data where measurements are required.
• Omitting the aircraft total time from the logbook entry.
• Failing to furnish the discrepancy list to the owner when the aircraft cannot be approved.
• Signing a return-to-service entry before all unairworthy discrepancies are corrected.