Focusing on an Aircraft Minimum Equipment List
Redundancy in design generally means that failure or malfunction of one component doesn’t mean instant failure of the entire system. In various design applications, redundancy is accounted for using backup components. One example of this might be a backup generator that kicks in when power is lost to a machine. In aviation, one example of redundancy involves equipment, instruments, or onboard systems that can be inoperative for a specific aircraft for a specific flight. This is what is known as an aircraft minimum equipment list.
Airworthiness quantifies a plane or other aircraft’s suitability for completing a flight safely. Items on a minimum equipment list are those that are inoperative without compromising the aircraft’s airworthiness. Equipment and parts that aren’t on the MEL must be fully functional for flight. Even if a plane that is scheduled to fly has nonfunctional equipment, the flight can proceed if the equipment is listed on the FAA minimum equipment list.
The MEL should not be confused with a list of aircraft required equipment, which might include components that don’t affect airworthiness, such as passenger comfort items. It is also distinct from an aircraft safety equipment list, which includes personal flotation devices and emergency equipment unrelated to airworthiness. MEL aviation isn’t about cutting corners to complete a flight, but it does allow an operator to postpone or defer maintenance of equipment, avoiding loss of revenue or passenger discomfort.