When considering a major alteration in accordance with a supplemental type certificate (STC), what must the approving mechanic verify?

In the context of major alterations involving a supplemental type certificate (STC), the approving mechanic must ensure both the compatibility of the STC with other alterations and that the STC specifically applies to the make and model of the aircraft in question.

Verifying that the STC is applicable to the make and model is crucial because an STC is issued for a specific configuration and type design. If an STC is applied to an aircraft that it was not designed for, it could lead to safety issues or regulatory violations.

Additionally, confirming that the STC is compatible with other alterations is essential to maintain the integrity of the aircraft's systems and to ensure that no conflicting modifications occur. For example, if a previous alteration impacts the performance or functionality of the new alteration permitted by the STC, it could compromise the aircraft’s safety and compliance with FAA regulations.

By ensuring both these points, the mechanic plays a vital role in maintaining safety, adherence to regulations, and the overall airworthiness of the aircraft. This thorough vetting process helps to prevent issues that could arise from improper modifications and ensures that the aircraft remains in compliance with its type certificate.