ATA 78 Engine Exhaust and Thrust Reverser


Procedures Required

(O) – An operational procedure
(M) or (M#) – A maintenance procedure
(O)(M) or (O)(M#) – Both operational and maintenance procedures

Repair Interval Categories

Category A

Items in this category shall be repaired within the time interval specified in the "Remarks or Exceptions" column of the air operator's approved MEL. Whenever the proviso in the "Remarks or Exceptions" column of the MMEL states cycles or flight time, the time interval begins with the next flight. Whenever the time interval is listed as flight days, the time interval begins on the flight day following the day of discovery.

Time Limited Dispatch - Some MMEL's for aircraft that are equipped with FADEC engines have relief that is subject to time limited dispatch expressed as a specific number of engine hours, and will start in accordance with the times established by the engine manufacturer or as indicated in the remarks column of the MMEL. Time limited relief cannot be extended.

Category B

Items in this category shall be repaired within 3 consecutive calendar days excluding the day of discovery.

Category C

Items in this category shall be repaired within 10 consecutive calendar days, excluding the day of discovery.

Category D

Items in this category shall be repaired within 120 consecutive calendar days, excluding the day of discovery. To be considered for placement in Category D, the item must be of an optional nature, or excess equipment which an air operator may, at his/her discretion, deactivate, remove from or install on an aircraft.

To be approved for Category D, the item must meet the following criteria:

  1. the absence of the item does not adversely affect crew member's workload;
  2. the crew members do not rely on the function of that item on a routine or continuous basis; and,
  3. the crew members' training, subsequent habit patterns and procedures do not rely on the use of that item.

Category D relief will generally not be approved for equipment which is considered to increase the level of safety, even if that equipment is of an optional nature.


System and Sequence No. Item Repair
Remarks or Exceptions
Thrust Reversers C - - (M)(O)

For large aircraft (more than 19 seats) at least 50% must be operative for dispatch provided:

a) inoperative thrust reversers are stowed and locked, and

b) applicable AFM performance penalties are applied.

C - - (M)(O)

For smaller aircraft (19 seats or fewer), both thrust reversers may be inoperative provided:

a) inoperative thrust reversers are stowed and locked, and

b) applicable AFM performance penalties are applied.


References:  FAA PL 26 (Rev. 1, 15 Aug. 1997)

The requirement for 50% of the thrust reversers on large aircraft (more than 19 seats) to be operative has been adopted from the FAA policy (TCA AARXB, 10 May 91 refers).  As an aside, it is noted that the FAA are considering requiring all thrust reversers to be operative for large two engine aircraft for increased safety (performance) reasons.  Thrust reverser asymmetry will have to be considered for the four-engine configurations to ensure a double-asymmetry condition is not permitted.  For these cases, inoperative thrust reversers should be located on symmetrical engines.

The JAA, in general, permit all thrust reversers to be inoperative as there is no airworthiness design requirement or performance credit given.  There is considerable FAA/JAA/TC activity regarding operation from wet and contaminated runways and in some instances performance will be based on credit for thrust reversers.  In these instances, dispatch would not be permitted or some sort of performance penalty would need to be applied.

The (M) and (O) procedures must address deactivation and operational procedures beyond those included in the AFM.

FAA Differences: Except for FAA inconsistencies, TCCA relief is identical.  FAA PL only addresses small turbojet airplanes.

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