When considering a major alteration under a Supplemental Type Certificate, what must be ensured by the approving mechanic?

When considering a major alteration under a Supplemental Type Certificate (STC), it is essential for the approving mechanic to ensure that the STC is compatible with other systems. This ensures that the alteration does not interfere with or negatively impact the operation of existing systems, components, and the overall safety and functionality of the aircraft. Compatibility checks are vital to maintaining the airworthiness of the aircraft after the alteration, as changes made under an STC should integrate seamlessly with current systems to avoid unintended consequences.

While other aspects such as the legality of the STC, compliance with certification rules, and FAA review are important, the direct focus on system compatibility is crucial for the mechanic to verify before proceeding with the alteration. Ensuring compatibility is a fundamental responsibility of the mechanic to uphold safety and regulatory compliance in aircraft modifications.