A configuration deviation list (CDL) is a list, established by the organization responsible for the type design with the approval of the State of Design, which identifies any external parts of an aircraft type which may be missing at the commencement of a flight, and which contains, where necessary, any information on associated operating limitations and performance correction. (ICAO Annex 6: Operation of Aircraft)
The CDL is usually prepared by the aircraft manufacturer and is part of the Aircraft Flight Manual (AFM).
The CDL is a listing of regulator-approved non-structural external parts that may be missing but the airplane remains airworthy. To qualify an item onto the CDL, a restrictive set of conditions must be met, e.g.:
- The effect of the missing part upon adjacent structure and systems must be evaluated.
- The effect upon airplane performance must be measured.
- The combined effect upon the aircraft when more than one CDL item is present must be determined (i.e. the effect of a combination of items missing).
Most items on the CDL are qualified during the initial certification of the airplane and CDL test flights are scheduled into the test plan.
The CDL should not be confused with the MEL (MEL). While the MEL describes the limitations of aircraft operation in case of a system being inoperative/having malfunctioned (e.g. transponder failure), the CDL deals with situations where external parts of an aircraft are missing/fallen off (e.g. fairings, aerodynamic seals or panels).
If a CDL for an aircraft type does not exist, then flying with external parts missing means that the aircraft is not in its original certificated configuration, thus, it is not airworthy.
Regulations and supplementary information concerning the CDL are contained in EU-OPS.