Policy Letter 139


Minimum Equipment List (MEL) Relief for Inoperative Flight Deck Door Lock

File Number

AARX 2204-5



Policy Statement

The purpose of this Policy Letter is to inform Commercial and Business Aviation Inspectors of the MEL process to be followed in the event that a flight deck door lock becomes unserviceable.


Air Carrier Security Measures, June 1, 1996, as amended by Message 2001M-500, dated October 1, 2001.


Message 2001M-500, Part A Section 5(1), Security of Aircraft requires the flight deck door to be "locked at all times from the close of doors with the intention of flight to the opening of doors upon arrival, unless there are overriding safety-of-flight considerations or the flight deck door is not equipped with a locking device".

This Message does not consider effective alternatives to the integral lock, such as a door-strengthening device, nor does it clearly address the case where a door lock becomes unserviceable during a multi-leg itinerary.

A flight deck door modified with a strengthening device, independent of the integral locking system, remains an effective barrier against flight deck intrusion. In this case, MEL relief will consider the presence of a redundant system.

Unmodified flight deck doors rely solely on the integral lock. While it may be argued that an aircraft with an unserviceable door lock incurs the same risk as one that is not equipped with a door lock, generally crews operating aircraft whose doors normally lock cannot follow their standard protocol when that lock becomes unserviceable. In these cases, relief is much more limited, in essence allowing the flight itinerary to progress toward a maintenance facility. As in all MEL applications, the operating crew retains the prerogative to decline MEL relief in the interests of security.


For flight deck doors modified with a door strengthening device: The flight deck door lock may be inoperative provided the door strengthening device is functioning at all times from the close of doors with the intention of flight to the opening of doors upon arrival, subject to overriding safety of flight conditions. This is a MEL category C item, valid for 10 days.

For flight deck doors equipped only with an integral lock: The flight deck door lock may be inoperative for a maximum of two flight sectors, MEL category A. Operators shall establish procedures to mitigate security concerns, such as increased supervision of the area(s) proximate to the flight deck door, possible restrictions on the use of lavatories where passengers may queue in the vicinity of the flight deck door, etc.

Principal Operations Inspectors or their delegates should advise their air operators regarding these new MEL requirements as soon as possible. MEL revisions and associated operational procedures in regards to the flight deck door lock shall be submitted for approval per standard procedures.

Please note that this Policy does not apply to operators whose MEL prohibits departure with an inoperative door lock.

Future Disposition

This Policy Letter will remain in effect until further notice.

Reference Number

This Policy Letter is designated AARX No. 139.

M.R. Preuss
Commercial & Business Aviation

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