What should you do if you find a discrepancy with an inoperative instrument required by the aircraft TCDS during an inspection?

When encountering a discrepancy with an inoperative instrument that is required by the aircraft Type Certificate Data Sheet (TCDS) during an inspection, the best course of action is to list it as unairworthy and document it. This is crucial because the TCDS specifies the equipment that must be operational for the aircraft to be considered airworthy. Identifying the instrument as unairworthy ensures that appropriate actions can be taken to address the issue before the aircraft is returned to service.

Documenting the unairworthy condition provides a formal record, which is essential for compliance with regulatory standards and for maintaining the safety of the aircraft. It also informs any subsequent maintenance personnel of the discrepancy and ensures that necessary repairs or replacements can be scheduled.

This course of action emphasizes the importance of adhering to regulations and guidelines outlined by aviation authorities, which uphold safety and operational integrity in aviation practices.