Federal Aviation


MMEL Policy Letter (PL) 77, Revision 4


December 17, 2012


All Region Flight Standards Division Managers

All Aircraft Evaluation Group Managers


Manager, Air Transportation Division, AFS-200

Reply to Attn of:

Manager, New Program implementation and International Support Branch,



Cockpit and Instrument Lighting Systems




PL-77, Revision 3, dated July 5, 2012

PL-77, Revision 2, dated March 12, 2012

PL-77, Revision 1, dated August 15, 1997

PL-77, Original, dated January 11, 1995


To provide standardized MMEL requirements for Cockpit/Flight Deck/Flight Compartment and Instrument Lighting Systems.

Revision 4 adds “Cockpit/Flight Deck” to item description; removes the proviso associated with emergency procedures because such dispatch restriction would be identified by MMEL PL 63, “Instrument and Equipment Items Required for Emergency Procedures”; clarifies that relief may be provided to non-essential Cockpit/Flight Deck/Flight Compartment and Instrument Lighting Systems that are on an emergency bus.

Revision 3 revises the proviso concerning systems on the emergency bus.

Revision 2 deletes the global change designation and expands upon the relief intended to be granted in MMELs. Relief for buttons/switch lights or individual annunciations in the cockpit must not be permitted with this PL. These buttons/switches should have relief provided on an individual basis. Any cockpit lighting system associated with an emergency electrical system must be excluded (e.g. cockpit floodlights or dome lights on some aircraft). This PL also includes a reference to operators with night vision goggles (NVG) systems.

Revision 1 is reformatted. The policy is unchanged.

Some aircraft manufacturers may choose to include non-essential Cockpit/Flight Deck/Flight Compartment and Instrument Lighting Systems on the emergency bus for convenience. Non-essential Cockpit/Flight Deck/Flight Compartment and Instrument Lighting Systems on an emergency bus may be considered for MMEL relief if no safety-of-flight issues exist and an acceptable level of safety is maintained.


Standardized MMEL requirements have been established for Cockpit/Flight Deck/Flight Compartment Lighting Systems and Instrument Lighting Systems. It is important to recognize that this MMEL relief applies only to flight compartment and instrument lighting; it does not apply to warning, caution or advisory lights. Warning and caution systems associated with the inoperative system must be operative unless specifically authorized by the MMEL.

The following standard MMEL proviso and repair category is an example of relief that may be granted in MMELs. Relief for individual button/switch lights and/or annunciations/indications is not intended to be included in this PL.


All Flight Operations Evaluation Board (FOEB) Chair must ensure that sufficient emergency lighting system lights are operative before granting this relief.


Repair Interval

Number Installed

Number Required for Dispatch

Remarks or Exceptions


Cockpit/Flight Deck/Flight Compartment and Instrument Lighting System




Individual lights may be inoperative provided:

a)            Remaining Lighting System lights are sufficient to clearly illuminate all required instruments, controls, and other devices for which they are provided,

b)          Remaining Lighting System lights are positioned so that direct rays are shielded from flight crewmembers eyes, and

c)            Lighting configuration and intensity is acceptable to the flight crew.

Note 1: Individual button/switch lights and/or annunciations/indications are excluded from this relief.

Note 2: Unaided operation (without NVGs) may be permitted with inoperative NVG supplemental lights; cracked or missing filters.


Each FOEB Chair should apply this policy to affected MMELs through the normal FOEB process.





Leslie H. Smith

Manager, Air Transportation Division