Federal Aviation


MMEL Policy Letter (PL)-98, Revision 1

Date:                                  June 1, 2017

To:                                     All Aircraft Evaluation Group Managers


From:                                 Manager, Air Transportation Division, AFS-200

Reply to                             Manager, New Program Implementation Branch, AFS-240

Attn of:                        



MMEL Code:       34 (NAVIGATION)

Reference:             Policy Letter 98, Revision Original, dated January 20, 1999

                             14 CFR §§ 91.213, 91.503, 91.1115, 121.628, 125.201, 129.14, 135.179

      AC 20-138, AC 20-153, AC 90-100, AC 90-101, AC 90-105

      Aeronautical Information Manual (AIM); MMEL PL-25

  Establish MMEL Relief for Inoperable Navigation Databases



Revision 1: corrects the regulatory non-compliance found in revision 0 for an out of currency navigation database; aligns allowable MMEL relief in accordance with the definition of “inoperative” found in MMEL PL-25; updates the repair category from repair category C to repair category A, ten (10) flight days; changes “Remarks or Exceptions” in accordance with repair category A and flight operations with an inoperative navigation database.


Revision 0: The original PL-98 established MMEL relief of an “out of currency” navigation database with repair category C.

A navigation database is any navigation data stored electronically in a system supporting navigation applications. Navigation data is information intended to be used to assist the pilot to identify the aircraft’s position with respect to flight plans, ground reference points and navaid fixes (such as VHF omni-directional radio ranges (VOR), nondirectional radio beacon (NDB), etc.) as well as some points on the airport surface. A navigation database may include an airport database but does not include other aeronautical databases such as an obstacle or terrain database.


Although a navigation database is software, it is considered an item within the aircraft that may be considered for MMEL relief per 14 CFR. However, for any item to be considered for MMEL relief it must be inoperative by regulation, and must meet the definition of inoperative in MMEL PL-25:

Inoperative: A system and/or component malfunction to the extent that it does not accomplish its intended purpose and/or is not consistently functioning normally within its approved operating limit(s) and/or tolerance(s).

An out-of-currency (aka: out-of-date or expired) navigation database does not meet the definition of inoperative and is not authorized MMEL relief per 14 CFR. A navigation database that is malfunctioning may be considered for MMEL relief with the appropriate provisos in the “Remarks or Exceptions” column that prohibit the use of the navigation database until repairs are made.


POLICY: nbsp;

1.   An inoperative navigation database may be authorized MMEL relief per 14 CFR.

2.   An out-of-currency or out-of-date navigation database is not authorized MMEL relief per 14 CFR.




Repair Interval

Number Installed

Number Required for Dispatch

Remarks or Exceptions



Navigation Database




May be inoperative provided:

a)        Operations do not require its use,

b)      It is not used in a primary navigation system required by 14 CFR,

c)        Alternate procedures are developed and used,

d)      The ICAO Flight Plan is updated (as required) to notify ATC of the navigation equipment status of the aircraft, and

e)        Is repaired within ten (10) flight days.

Note: An out-of-currency or out-of-date navigation database is not authorized MMEL relief per 14 CFR.



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





Jodi Baker

Acting Manager, Air Transportation Division