An STC is required for a major alteration to an aircraft. A major alteration could include significant changes to items such as weight, balance, structural, operation, flight characteristics of an aircraft.

In general, installation of avionics systems that do not perform critical functions, other than basic attitude, altitude, and airspeed instruments, or are highly integrated with complex switching interfaces with other equipment and systems may be eligible for field approval.

Southeast Aerospace follows FAA Order 8900.1 Volume 4 Chapter 9 which provides specific instructions and guidelines to determine what is considered a major alteration and when an STC or Engineering Data is required for an installation. This document indicates the types of systems that may require an STC or specific Engineering Data (ENG) and those that may be evaluated (EVL) for other types of approval. For example, certain systems such as synthetic vision systems (e.g. glass cockpit), TCAS II, autopilots, FDR, EFIS always require an STC. Systems such as CVR, non-TCAS II traffic systems, GPS, and MFD may only require other types of approval.

It is always recommended that the approved installer or installing agency refer to all applicable regulatory guidelines, installation data, and procedures before performing any installation. For complete details field approvals from FAA Order 8900.1 , click Here. This document is provided for reference only. Please visit the FAA website to ensure you have the latest revision.