Can accomplishment of an action required by an AD be deferred in accordance with the instructions of approved (M)MEL?
Answer
Certain ADs require actions (e.g., inspections and possible corrective actions; modification) on airframe and engine parts, equipment or systems for which design approval holder (DAH) configuration deviation list (CDL) and master minimum equipment list (MMEL) items are published.
As a general rule: unless clearly stated in the AD, it is not allowed to postpone the action required by the AD using the instructions of a DAH CDL or MMEL item, as applicable.
When allowed, the AD will have a statement as follows (or similar):
“Accomplishment of the action(s) on an aircraft, as required by paragraph (x) of this AD, can be deferred in accordance with the applicable instructions and limitations of the [TCH product designation] Master Minimum Equipment List (MMEL) item AA-BB-CC [or CDL, as applicable]”, provided that the affected MMEL item AA-BB-CC is included in the operator approved Minimum Equipment List (MEL) [or the approved Aircraft Flight Manual].
“As an alternative to the requirements of paragraphs (x) and (y) of this AD, marking an affected part inoperative, and assuring that that part is not activated during flight operations, is an acceptable alternative method to defer compliance with the requirements of paragraph (x) and (y) of this AD for that part, provided this is accomplished within the provisions of the applicable master minimum equipment list (MMEL) included in the operator approved MEL”.
Airworthiness Limitations Section (ALS) AD
As an exception to the general statement above, MMEL items are accepted as “applicable DAH maintenance documentation” as referenced in the ALS-AD paragraph requiring accomplishment of corrective actions (standard wording quoted below):
Corrective Actions: In case of finding discrepancies (as defined in the ALS) during accomplishment of any task as required by paragraph (1) of this AD, within the compliance time specified in the ALS, accomplish the applicable corrective action(s) in accordance with the applicable [DAH] maintenance documentation. If no compliance time is identified in the ALS, accomplish the applicable corrective action(s) before next flight. If a detected discrepancy is not identified in the ALS, before next flight, contact [TCH] for approved instructions and accomplish those instructions accordingly.
In other words, if, during the accomplishment of an ALS inspection or check, a discrepancy is found, for which the rectification can be deferred in accordance with the operator’s MEL approved by the competent authority, that deferral is accepted as method to temporarily comply with the applicable ALS AD requirement.