ATA 24 Electrical Power

LEGEND

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.

ITEM:  24-00-1  ELECTRICAL POWER SOURCES AND BUS TIES

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions
Electrical Power Sources and Bus Ties B/C - - See DISCUSSION.

DISCUSSION:

References:   TC TP 6327 (ETOPS), FAA PL 27 (Rev. 1, 15 Aug. 1997), PL 40 (Rev. 1, 15 Aug. 1997), PL 64 (Rev. 1, 15 Aug. 1997), FAA PL 107 (Rev. 1, 22 May 2001), FAA AC 120-42B

To the extent possible, the MMEL shall be constructed such that after any subsequent single in-flight electrical power system failure, sufficient instruments and equipment remain operative to provide for navigation, communications, and aircraft operation and monitoring.  Such systems must remain operative for the period of time which is limited only by the range of the airplane.  For these purposes, battery power may not be considered a power source.

For 3 and 4 engine aircraft, a category C may be applicable where more than two power sources are available. Justification for this MMEL relief may require an electrical load analysis assuming the next worst subsequent electrical failure (loss of power source) has occurred, in order to demonstrate capability for continued safe flight without a cascade failure effect upon other electrical sources or loss of essential services.  It may be necessary to implement electrical load shedding procedures to substantiate acceptable electrical loads when dispatching with a power source inoperative.  For new items or new aircraft a load analysis and load shedding procedures are required.

Relief must take into consideration ETOPS/EROPS requirements.

FAA Differences:  FAA relief is similar to TCCA.

ITEM:  24-00-2  ELECTRICAL POWER SOURCE MONITORING DEVICES

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions
Electrical Power Source Monitoring Devices C - 0 May be inoperative when the associated power source is inoperative.
B - - See DISCUSSION.

DISCUSSION:

References:  nil

In general, electrical power source monitoring devices (voltmeters, loadmeters, temperature indicators and caution/warning lights) may be inoperative if dispatch is permitted with the associated power source inoperative.  MMEL relief may be restricted to a specific monitoring equipment channel(s) associated with inoperative/disabled electrical power sources. Relief has been permitted with monitoring devices inoperative (e.g. B1900, SA226/227) with considerations such as load requirements within the capability of one generator, associated light annunciator is operative, and in some cases no flight in icing conditions, VMC, VFRetc.

FAA DifferencesFAA relief is similar to TCCA.

Date modified: