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Minimum Equipment List (MEL
One major difference between most general aviation piston aircraft, and turbine-powered corporate or airline aircraft, is the extensive redundancy of aircraft systems. In order to ensure safety and reliability, most major system components and communications and avionics equipment are duplicated. In many cases this allows corporate and airline aircraft to safely operate even after failure of individual aircraft components.
A MEL (FAA-approved Minimum Equipment List) contains items that are allowed to be inoperative on a given aircraft, while it is still considered airworthy. MELs are important because they allow flights to be conducted even though certain equipment is inoperative, while still being considered legal and “safe” by the FAA.
The MEL, which must always be onboard the aircraft, is normally in notebook form and is fairly simple to use. When an aircraft has an inoperative component, the pilots look it up in the MEL. The MEL states what flight conditions, performance limitations, crew operating procedures, maintenance procedures, placards, and duration limits are necessary in order to be legal for flight with that component inoperative. The idea is to ensure that acceptable safety levels are maintained, while allowing the aircraft operator maximum utility from its fleet.
When using a MEL, a few important things should be kept in mind. All equipment not listed in the MEL and related to the aircraft’s airworthiness must be operative (that is, aircraft wings must be intact and in good condition). The airplane may not be operated if any OTS (out-of-service) components are not specifically listed in the MEL or if any MEL items are out of date. (MEL items are coded to show how long the aircraft may be operated before they are repaired.)
When multiple components are inoperative, pilots must consider the combined effects on aircraft safety and crew workload in order to establish the airplane’s airworthiness. As with everything in flying, ultimate responsibility for maintaining acceptable levels of safety rests with the flight crew.
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FIGURE 12.2 | Exterior preflight inspection.
