Federal Aviation

MMEL Policy Letter 45  Revision 2


March 4, 2004


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


Time Limited Dispatch (TLD) Authorization for Full Authority Digital Electronic Control (FADEC) Engines


73 (Engine Fuel and Control)


1.  Policy Letter ANE-1993-33.28TLD-R1, "Policy for Time Limited Dispatch (TLD) of   Engines Fitted with Full Authority Digital Engine Controls (FADEC) Systems", dated June 29, 2001.

2.  PL-45, Revision 1, dated August 15, 1997, reformatted only

3.  FAA Engine and Propeller Directorate Policy Letter on "Time Limited Dispatch of Engines Fitted with FADEC Systems", dated October 28, 1993.



The purpose of this policy letter is to provide guidance to the Flight Operations Evaluation Board (FOEB) for establishing Master Minimum Equipment List (MMEL) relief for Time Limited Dispatch (TLD) of Full Authority Digital Electronic Control (FADEC) engines and to operators and PMIs/PAIs/POIs for development of MELs.



Revision 2:  Addresses the changes contained in the revised FAA Engine and Propeller Directorate Policy Letter (Reference 3).  This revision also recognizes the fact that aircraft manufacturers may choose to be more restrictive with TLD operations than those limitations certified with the engine.  When this occurs, the aircraft manufacturer’s limitations (more restrictive) must be stated in the operator’s MEL.  This revision adds Background information and includes a complete rewrite of the Discussion section. POLICY statement revised for clarity.


Revision 1:  Reformats Policy Letter 26 with no change to policy.



The incorporation of FADEC systems on aircraft engines has introduced certain changes in the FAA certification process, which allow for a detailed analysis of FADEC system redundancy in order to qualify the engine for TLD approval.  The FAA Engine and Propeller Directorate (EPD), ANE-100, in coordination with Flight Standards, issued the original Reference 1 policy letter on TLD in 1993 to enable consistent certification and application of TLD.  Following this, the FAA Flight Standards Air Transportation Division, AFS-200, issued the Reference 2 revision to PL-45 to address the implementation aspects of the Reference 1 EPD policy letter.  Since then, EPD in coordination with Flight Standards issued a revised TLD policy letter, Reference 3, in 2001. 


In accordance with the latest Reference 3 EPD policy letter, dispatch of an aircraft with engines having FADEC system faults is allowed provided: 1) the engine model has TLD approval via FAA certification, 2) the faults are not in the “No Dispatch” category, and 3) the operator’s repair of the faults is managed by adherence to one or a combination of the following approaches: a) MEL relief for the faults, or b) an FAA approved scheduled periodic inspection and repair maintenance program.  If dispatch with any FADEC system faults is to be handled by an operator’s MEL, then TLD relief for these faults must be part of the aircraft MMEL.  The approach to be used by the operator is usually established at aircraft certification.


This Policy Letter is intended to address those aircraft where the MEL is being used to address some (or all) of the FADEC system’s dispatchable faults.


TLD allows an operator to dispatch with known faults for a limited period of time before maintenance is performed.  Specific time limits and categories are addressed via:

1.            A note on the Engine TCDS, which will contain the specific time limit information or reference an FAA-approved engine manufacturer document which contains the required information; or, alternately, a note on the TCDS which simply indicates that the engine has been approved for TLD operations, accompanied by the incorporation of the TLD related information in the Airworthiness Limitations Section (ALS) of the engine Instructions for Continued Airworthiness (ICAs). 

2.            The above engine TLD information may be augmented with a note on the Aircraft TCDS, which indicates that the aircraft manufacturer has further restricted the engine TLD limitations, accompanied by incorporation of the more restrictive TLD information in the ALS of the aircraft ICAs. 


In those instances where both the engine and aircraft manufacturer provide TLD restrictions, the FOEB must use the more restrictive requirements.  If the aircraft manufacturer mandates more restrictive requirements than the engine manufacturer with regard to TLD time limits or with the categories into which some FADEC system faults have been assigned by the engine manufacturer, the aircraft manufacturer should explicitly state this when specifying the aircraft’s TLD related limitations.  This will help ensure that the FOEB does not inadvertently use the engine manufacturer’s published limitations.


Although the required repair intervals may vary from engine to engine, the following is one example developed by an engine manufacturer for showing three categories of fault levels identified under the TLD concept and their associated time limitations:


a.            No Dispatch                           0 hrs.

b.            Short-Time Dispatch               125 flt. hrs.

c.            Long-Time Dispatch                250 flt. hrs.

Under the terms of TLD approval, the operator is allowed to defer short-time and long-time faults up to their specified time limits, at which time repair of the faults is required.


The TLD maintenance requirements are part of the FAA certification process and appear on the engine TCDS and/or ALS of the engine ICAs, and may be augmented by information in the aircraft TCDS and/or ALS of the aircraft ICAs.  They are the responsibility of the FAA’s Engine and Aircraft Certification Offices with respect to approval and time escalation.  An aircraft manufacturer should not propose any time limits for the various FADEC system faults that would be greater than the time limits established by the engine manufacturer without coordination with both the FAA and engine manufacturer.


Additionally, for TLD authorization and continuation of the deferral privilege, the operator must provide failure data derived from FADEC memory (i.e., reliability monitoring data) on a regular basis.  These data are to be reported to the engine manufacturer for forwarding to the appropriate Engine Certification Offices.


To prevent potential conflicts between TCDS/ALS information and MMEL requirements, PMIs/PAIs/POIs should ensure that:


a.            MELs are developed with FADEC references specifically addressing their operator’s equipment and applicable TCDS/ALS limitations.  With respect to FADEC system TLD operations, the more restrictive of the engine or aircraft manufacturer’s limitations must be applied.

b.            TCDS/ALS controlled items identified as such within the MEL are not extended under the current MEL extensions philosophy.

c.            TLD certification (i.e., repair) requirements are accomplished within the established time limits.

d.            TLD certification requirements (i.e., time limits) are not adjusted or extended without FAA engineering approval, unless it is indicated that temporary extensions are allowable in the engine ALS.

e.            TLD reliability reporting requirements are being met.

f.                Operators are advised that failure to comply with the engine or aircraft TCDS/ALS requirements related to TLD, whichever is more restrictive, would be contrary to the intent of MMEL relief, and could result in loss of TLD authorization.


The MMEL phraseology has been developed in generic terms in lieu of expressing specific TLD time limits for the following reasons:


a.            Standardizes all MMELs.

b.            Eliminating the need to interpret and/or compare from other related MMELs.

c.            Will eliminate the need to revise the MMEL in the event that time limits and/or other requirements are adjusted by FAA certification.


The specific time limits should be incorporated in the Operator’s MEL.



The following provisions will be included in the MMEL and appear under the appropriate ATA chapter.  The statement below should be used as guidance in the development of MMEL TLD items associated with FADEC engines.  It is important to note that the following example of this generic phraseology is only a guide and is not intended for use as stated.









Engine FADEC System










1) System Faults




May be dispatched with system faults provided repairs are made in accordance with the times                     established in either the engine or aircraft  manufacturer’s, FAA approved document,                    whichever is more restrictive (reference specific document number).







Each Flight Operations Evaluation Board (FOEB) chairman should apply the following policy to affected MMELs through the normal FOEB process.



Matthew J Schack, Manager

Air Transportation Division AFS 200



PL-45, R 2 reformatted 01/20/2010 with no change in content