Who is responsible for ensuring that materials used in aircraft maintenance meet the proper standards?

The responsibility for ensuring that materials used in aircraft maintenance meet the proper standards rests primarily with the installing person or agency. This entity is tasked with making sure that all parts and materials utilized in maintenance, repairs, or modifications comply with the applicable regulations and standards set forth by aviation authorities. They must ensure that the materials are not only approved and certified but also suitable for the specific type of aircraft and the particular maintenance task being performed.

Regarding other choices, while the pilot in command holds significant responsibilities related to the operation and safety of the flight, their role does not extend to the verification of materials used in maintenance. Similarly, the regulatory body establishes the standards and guidelines but is not directly involved in the day-to-day verification of components used in maintenance by individual operators. The aircraft owner indeed has vested interest and should be informed about the maintenance processes, but it is the installing person or agency that has the direct responsibility to ensure compliance with standards during maintenance.