Which type of approval must an altimeter have to be installed on a civil aircraft?

An altimeter installed on a civil aircraft must have a Technical Standard Order (TSO) authorization. TSOs are minimum performance standards issued by the Federal Aviation Administration (FAA) for specified materials, parts, and appliances used on civil aircraft. When an altimeter is produced under a TSO, it means that it has met the FAA's rigorous criteria for performance and reliability, ensuring that the device will function correctly in the aircraft environment. This certification process is crucial for maintaining the safety and airworthiness of the aircraft.

While other options such as Supplemental Type Certificates (STCs) and Production Certificates (PCs) relate to broader aspects of aircraft modifications and part manufacturing respectively, they do not specifically guarantee that an altimeter meets the necessary technical standards required for installation. The Standard Equipment Authorization is less commonly referenced in this context and does not specifically pertain to altimeter compliance under FAA guidelines. Thus, TSO is the clear requirement for altimeter installation.