ATA 47 Inert gas system


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
Nitrogen Generation System C - 0 If required by certification or operating rules.
D - 0 If not required by certification or operating rules.


References:  FAA PL 118 (Original, 1 June 2006)

Nitrogen Generation System (NGS) is optional equipment that is not required to be installed on airplanes.  NGS provides a new flammability reduction means that uses a nitrogen generation system to reduce the oxygen content in the fuel tank so that exposure to a combustible mixture of fuel and air is substantially minimized.  This GB item is intended to promote the installation of NGS, especially during the early stages of installation by production and retrofit, when in-service problems would be more likely to occur.

FAA Differences:  FAA relief is identical to TCCA.

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