Federal Aviation

MMEL Policy Letter (PL) 63, Revision 4


July 5, 2012


All Region Flight Standards Division Managers
All Aircraft Evaluation Group Managers


Manager, Air Transportation Division, AFS-200

Reply to Attn of:

Manager, Technical Programs Branch, AFS-260


Instrument and Equipment Items Required for Emergency Procedures


00 (General)


PL-63, Revision 3, dated January 29, 2004

PL-63, Revision 2, dated unknown

PL-63, Revision 1, dated December 23, 1993

PL-28, item 8, dated May 19, 1987


To ensure that the instrument and equipment items necessary for the accomplishment of emergency procedures are not given relief in the MMEL


Revision 4 clarifies MMEL relief may be provided for redundant instrument and equipment items used to accomplish an emergency procedure.

Revision 3 removes the e.g. (for example) in the POLICY statement since it may lead to misinterpretation. Removal of the example does not change the intent of the policy.

Revision 2 reformats Policy Letter 63 with no change to policy.

Revision 1 was accomplished 12/23/1993.

During a previous regulatory process, two comments were made reference Title 14 of the Code of Federal Regulations (14 CFR) 121.628, Inoperable Instruments and Equipment. The two comments stated that pilots cannot always comply with the emergency checklist procedures because one or more aircraft systems or components required to accomplish the emergency procedure is inoperative. These comments suggest the rule be amended so that no instrument or equipment item required to accomplish an emergency procedure be included on an MMEL.

The preamble to the MMEL states, "The MEL must not deviate from Aircraft Flight Manual Limitations, Emergency Procedures or Airworthiness Directives." However, most of the MEL problems seem to involve systems or components which are powered by an aircraft's emergency or battery bus. For example:

1. The Douglas DC-9 Flight Handbook, Emergency Procedures, directs the pilot to turn his emergency power switch on when a complete electrical failure occurs in-flight. With the emergency power on, the only communications system available is the number one system and the only navigational system available is the number one system.

2. The Boeing 727 Airplane Flight Manual, Emergency Procedures, directs the pilot to switch the essential power selector to "Stand-by" when a loss of all generators occurs. With the standby power on, the only communication system available is the number one system and the only navigation system available is the number one system.

Most MMELs state in the Remarks Column "As required by 14 CFR" for the VHF Communications and VHF Navigation (VOR/ILS) Systems. Safety is impacted if an aircraft is allowed to be dispatched (or flight released) with an inoperative communication or navigation system powered by an emergency bus. An emergency would require the flightcrew to switch to emergency power and the inoperative system powered by the emergency bus would not be available to the flightcrew.


1.      Each Flight Operations Evaluation Board (FOEB) Chairman will ensure that MMELs do not provide relief to instrument and equipment items that are required to accomplish emergency procedures.

2.      Relief may be considered for redundant instrument or equipment items powered by the same (or redundant) power source utilized to accomplish the emergency procedure. FOEB Chairmen must ensure that the accomplishment of emergency procedures remains the priority when considering this relief.

Each FOEB Chairman should apply this Policy to affected MMELs through the normal FOEB process.






Leslie Smith

Manager, Air Transportation Division