What is the primary purpose of a minimum equipment list (MEL) in aviation?

The primary purpose of a minimum equipment list (MEL) is to identify the specific equipment on an aircraft that may be inoperative without compromising the overall safety and airworthiness of the aircraft. The MEL is an essential tool for flight operations, enabling pilots and maintenance personnel to make informed decisions about whether the aircraft is safe to operate despite certain items being inoperative. This list clarifies that while some equipment may be malfunctioning, it does not affect the aircraft's ability to safely conduct its flight missions.

Each item listed in the MEL is carefully evaluated based on the regulations and guidelines established by aviation authorities, ensuring that the aircraft can still be operated safely with those items inoperative. This allows flexibility in flight scheduling and helps prevent downtime due to minor equipment failures that do not impact the aircraft's overall safety.

In contrast, the other options address different aspects of aircraft equipment requirements. There are established lists defining equipment that must always be operational or that must be installed in compliance with airworthiness directives, but these do not specifically serve the function of the MEL, which is focused on what can be safely inoperative.