When is a mechanic responsible for checking AD compliance?

The correct response highlights that a mechanic is responsible for checking Airworthiness Directives (AD) compliance when performing an inspection required under part 91, 125, or 135 of the Federal Aviation Regulations. This is crucial because inspections conducted under these parts are mandated for ensuring the safety and airworthiness of aircraft. ADs are legally enforceable rules issued by the Federal Aviation Administration (FAA) to address specific safety concerns identified in aircraft, engines, propellers, and appliances.

During these inspections, mechanics must thoroughly review compliance with any applicable ADs to confirm that the aircraft meets regulations and is safe for operation. This ensures that any necessary repairs, modifications, or maintenance related to the AD are performed, thus upholding aviation safety standards.

While checking AD compliance could happen after any flight, during regular maintenance, or when notified by the owner, these situations are not as clearly defined or mandated as inspections conducted under the specified parts of the regulations. Hence, the responsibility associated with inspecting for AD compliance is specifically tied to these required inspections, making this option the best answer.