Federal Aviation

MMEL Policy Letter 127, Revision 0


June 07, 2010


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



PL-127 is designated as GC-166


This GC is an approved addendum to all existing MMEL documents.  The operator may seek use of the specific relief contained in the policy letter by revising the Minimum Equipment List (MEL).  In doing so, the sample proviso stating the relief in the policy letter must be copied verbatim in the operator's MEL.  Approval of the revised MEL is gained utilizing established procedure, through the assigned Principal Operations Inspector (POI).





Night Vision Imaging Systems (NVIS)




33 (Lights)


Technical Standard Order, TSO-C164, Sept 30, 2004

FAA Order 8900.1, Vol 4, Chap 4, Para 4-627 (D)

FAA Order 8900.1, Vol 4, Chap 4, Para 4-637 (A)


The purpose of this Policy Letter is to provide standardized Master Minimum Equipment List (MMEL) requirements for operations of NVIS modified aircraft with inoperative NVIS lights, cracked, or missing filters.


Helicopter Emergency Medical Service (HEMS) operators are installing Night Vision Imaging Systems (NVIS) in their helicopter air ambulance aircraft.  Approximately 40% of the helicopter air ambulance fleet is equipped with NVIS modifications via STCs. Currently there is no relief for inoperative equipment in helicopter MMELs for NVIS lighting.  Aircraft equipped with the STCs are currently grounded for all operations until repairs are accomplished.  It has been determined that an acceptable level of safety is maintained for unaided (non-NVG) NVIS operations, not to exceed 10 days providing the defective NVIS lighting does not interfere with the pilot’s ability to see instruments, instrument markings, switch positions and frequency settings, and annunciations



Aircraft with defective NVIS lighting systems (inoperative supplemental lights, cracked, or missing filters), can operate using MMEL relief for day or night operations in VFR, or IFR, as long as NVGs are not used.  Unaided flight operations are allowed providing the NVIS lighting defect still allows the pilot to see instruments, instrument markings, annunciations, and switch and frequency settings.  The Flight Operations Evaluation Board (FOEB) Chairman should incorporate this policy through the normal FOEB MMEL revision process. 



MMEL Remarks Example:


NVG Compatible               C      -       -             Unaided operation (without NVGs)

Lighting System                                                may be permitted with inoperative

                                                                          NVG supplemental lights; cracked

                                                                          or missing filters;

                                                                          provided the remaining lights are:

                                                                          a)  sufficient to clearly illuminate

                                                                               all required instruments, controls,

                                                                               and other devices for which they

                                                                               are provided.

                                                                          b)  Positioned so that direct rays are

                                                                               shielded from flight crew-members

                                                                               eyes, and

                                                                          c)  Lighting configuration and intensity

                                                                               is acceptable to the flight crew.




Each Flight Operations Evaluation Board (FOEB) Chairman should apply this Policy to affected MMELs through the normal FOEB process.







John Duncan, Manager,

Air Transportation Division, AFS-200