ATA 21 Air Conditioning

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:  21-20-1  RECIRCULATION FANS

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions

Recirculation fans

C - 0 (M)(O)

May be inoperative provided:

a) Both A/C packs and pressurization system operate normally, and

b) Cargo is not carried in the associated compartment.

NOTE:
Unit Load Devices (ULDs) may be carried provided no cargo is carried on or in these devices.  For ballast purposes, use of bags (made of glass fibre or kevlar) of sand or ingots of non-magnetic metals (such as lead) is acceptable.

DISCUSSION:

References:  nil

This item only addresses recirculation fans exhausting through the cargo compartments.  Aircraft certification requirements such as smoke detection capability with inoperative recirculation fans must be considered when developing MMEL relief.

FAA Differences:  FAA relief is similar to TCCA.

ITEM:  21-30-1  AIR CONDITIONING AND PRESSURIZATION CONTROL MODES

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions
Automatic Pressurization Control Systems. C 2 1   May be inoperative provided the manual pressurization control system and one autopilot are operative.
Automatic Pressurization Control Systems. C 2 0 (M)(O)

May be inoperative provided:

a) Flight is conducted in an unpressurized configuration at or below 10,000 ft MSL, and

b) Cargo is not carried in associated compartment.

NOTE:
Unit Load Devices (ULDs) may be carried provided cargo is not carried on or in these devices.  For ballast purposes, use of bags (made of glass fibre or kevlar) of sand or ingots of non-magnetic metals (such as lead) is acceptable.

Automatic and Manual Pressurization Control Systems

C/D - 0 (M)(O)

May be inoperative provided:

a) Flight is conducted in an unpressurized configuration at or below 10,000 ft MSL,

b) Extended overwater operations are prohibited, and

c) Cargo is not carried in associated compartment.

NOTE:
Unit Load Devices (ULDs) may be carried provided cargo is not carried on or in these devices. For ballast purposes, use of bags (made of glass fibre or kevlar) of sand or ingots of non-magnetic metals (such as lead) is acceptable.

DISCUSSION:

References:   CAR 605.31, CAR 605.32

This item is an example and relief for a specific aircraft will need to be tailored accordingly.  For example, depending on the workload assessment it may not be necessary to have an operative autopilot in a manual pressurization situation.

The relief proposed above is based on the premise that the air conditioning packs are operating normally. In permitting auto and/or manual modes to be inoperative it must be assured that AFM emergency procedures can be accomplished.

(O) addresses unpressurized flight and manual pressurization.  (M) addresses operability of required equipment, e.g. outflow valves for smoke clearing, autopilot, if required.

If no specific unpressurized configuration is defined in the AFM, it must be confirmed that the aircraft has met its basis of certification when unpressurized.  If an unpressurized configuration has been certified, adequate procedures must be provided to ensure a smoke removal capability.  Based on certification findings, an unpressurized configuration must account for smoke clearance, electrical equipment cooling, ditching, and ventilation.  A cat D may be allowable for some aircraft and not for others, e.g. the B767 is assigned a cat C for unpressurized flight and this has been accepted by Transport Canada.  In some cases the cargo compartment fire detection/extinguishing system may have been certified only with a fully operative air conditioning system.  Therefore, when parts of the air conditioning system are inoperative, the smoke detection/fire extinguishing system must also be considered inoperative.  In this case the MMEL must include a proviso that the affected compartment be empty.  Carriage of non-combustible materials is not an acceptable alternative as no satisfactory definition of ”non-combustible materials” has ever been agreed.

FAA Differences:  The FAA definition of non-combustible materials is slightly different than that of TCCA.

ITEM:  21-30-2  OUTFLOW/SAFETY VALVES

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions

Outflow/Safety Valves

C - - (M)(O)

May be inoperative provided:

a) Affected valve(s) is secured OPEN,

b) Flight is conducted in an unpressurized configuration at or below 10,000 ft MSL, and

c) Extended overwater operations are prohibited.

DISCUSSION:

References:  AWM 525.801, FAR 1.1

Relief has been granted for outflow valve(s) inoperative open, however there are several things to consider:

1. Depending on their location, emergency procedures may require that the outflow valves be closed prior to ditching in order to prevent water from entering the aircraft.  Hence the proviso to not operate over water greater than 50 nautical miles from shore (this is considered equivalent to the FAA “extended overwater operation” definition FAR 1.1).

2. Procedures must be established for operating the aircraft unpressurized.

Relief may be granted for outflow valve(s) inoperative closed, howeversmoke removal tests must be reviewed in order to determine the acceptability of permitting any outflow valve(s) inoperative closed.  It may not be possible to dispatch with all valves inoperative closed because of smoke removal considerations and the possibility of over pressurization.

FAA Differences:  FAA relief is similar to TCCA.

ITEM:  21-30-3  CABIN ALTITUDE INDICATOR

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions

Cabin Altitude Indicator

C - 0 (O)

May be inoperative provided:

a) The cabin differential pressure indicator is operative, and

b) A chart is provided to convert cabin differential pressure to cabin altitude.

D - 0 (O) May be inoperative provided flight is conducted in an unpressurized configuration at or below 10,000 ft MSL.

DISCUSSION:

References:  nil

See item 21-30-1 DISCUSSION for unpressurized flight considerations.

The (O) for unpressurized flight will ensure that the procedures are clearly defined for the flight crew members.

FAA Differences: TCCA permits a category D for unpressurized flight whereas the FAA assigns a category C.

ITEM:  21-30-4  CABIN ALTITUDE WARNING SYSTEM

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions

Cabin Altitude Warning System

C 1 0  

May be inoperative provided flight is conducted at or below 10,000 feet MSL.

DISCUSSION:

References:  nil

The cabin altitude warning system provides an alert when the cabin altitude reaches some pre-selected altitude such as 10,000 ft above MSL. Frequently monitoring the cabin altitude during flight above this altitude is not considered sufficient to permit dispatch with the warning system inoperative.

FAA Differences:  FAA relief is identical to TCCA.

ITEM:  21-30-5  CABIN RATE OF CLIMB INDICATOR

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions

Cabin Rate of Climb Indicator

C 1 0  

May be inoperative provided flight is conducted at or below 10,000 feet MSL.

D 1 0 (O) May be inoperative provided flight is conducted in an unpressurized configuration at or below 10,000 ft MSL.

DISCUSSION:

References:  nil

See item 21-30-1 DISCUSSION for unpressurized flight considerations.

The cabin rate of climb indicator provides immediate feedback if operating in manual mode. Without this feedback the workload could be unacceptably high; therefore the proviso that all other aspects of the pressurization system must operate normally.

Some aircraft may have sufficient redundancy such that the next single failure does not result in manual mode, e.g. an aircraft may have two automatic pressurization systems. For these aircraft it would not be necessary that all other functions of the pressurization system be operative, see B767.

FAA Differences:  TCCA permits a category D for unpressurized flight whereas the FAA assigns a category C.

ITEM:  21-30-6  DIFFERENTIAL PRESSURE INDICATOR

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions

Differential Pressure Indicator

C 1 0 (O)

May be inoperative provided:

a) The cabin altitude indicator is operative, and

b) A chart is provided to convert cabin altitude to cabin differential pressure.
 

D 1 0 (O) May be inoperative provided flight is conducted in an unpressurized configuration at or below 10,000 ft MSL.

DISCUSSION:

References:  nil

See item 21-30-1 DISCUSSION for unpressurized flight considerations.

FAA Differences: TCCA permits a category D for unpressurized flight whereas the FAA assigns a category C.

ITEM:  21-50-1  AIR CONDITIONING PACKS

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions

Air Conditioning Packs

C 2 1 (O)

Except for extended range operations, one may be inoperative provided flight is conducted at or below FL XXX.

D 2 0 (M)(O)

May be inoperative provided:

a) Flight is conducted in an unpressurized configuration at or below 10,000 ft MSL,

b) Both recirculation fans, if installed, are operative, and

c) Cargo is not carried in associated compartment.

NOTE:
Unit Load Devices (ULDs) may be carried provided cargo is not carried on or in these devices. For ballast purposes, use of bags (made of glass fibre or kevlar) of sand or ingots of non-magnetic metals (such as lead) is acceptable.

Pack supporting Class C Fire Protection/Fire Detection on Main Deck Combi/All Cargo Configurations C - -  

May be inoperative provided main deck cargo is not carried.

NOTE:
Unit Load Devices (ULDs) may be carried provided cargo is not carried on or in these devices. For ballast purposes, use of bags (made of glass fibre or kevlar) of sand or ingots of non-magnetic metals (such as lead) is acceptable.

DISCUSSION:

References:  FAA PL 40 (Rev. 1, 15 Aug. 1997)

This item is an example and for each aircraft the associated justification will specify the maximum operating altitude.  This may be a function of the effects of a further failure e.g. loss of the remaining Air Conditioning Pack and also of the continued availability of essential functions such as smoke clearance.  For both Air Conditioning Packs inoperative, there will need to be appropriate altitude restrictions based on compliance with CARs relating to unpressurized flight and limitations arising from certification in this configuration.

No extended range operations permitted.

See item 21-30-1 for the DISCUSSION regarding unpressurized flight conditions.

For dispatch with one air conditioning unit or one bleed inoperative, the MMEL should specify the maximum operating altitude, which would have been determined during certification smoke clearing tests.
For both Air Conditioning Packs inoperative there will need to be appropriate altitude restrictions based on certification tests and no Extended Range Operations. On combi/all cargo, relief for the pack supporting fire protection/fire detection is possible if cargo is not carried in the main deck cargo area configurations.

The (O) procedure in the C 2 1 relief is intended to include procedures to ensure that flight attendant(s) is(are) advised of inoperative A/C Packs.

FAA Differences:  FAA relief is similar to TCCA.

ITEM:  21-50-2  EQUIPMENT AND AVIONICS COOLING FANS

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions

Equipment and Avionics Cooling Fans

C - -  

Relief dependent upon certification requirements (see discussion).

DISCUSSION:

References:  nil

Cooling fans are often installed to provide supplemental cooling to aircraft equipment as a means of providing a stable reduced operating temperature to enhance reliability of the equipment or to prevent the equipment from exceeding its thermal limitation thereby resulting in failure of the unit.

Equipment and/or avionics cooling fans may be inoperative provided it can be demonstrated that the equipment for which the fan has been installed does not exceed its operating thermal limit in the absence of supplemental cooling. The air temperature of the cabin, flight compartment and/or equipment location area may need to be restricted to defined values and/or exposure periods of elevated temperatures during which the protected equipment may operate without convective cooling provided by a fan(s).

If the function of the equipment being protected from excessive temperatures is deemed to be non-essential to continued safe flight and landing or for which dispatch relief has already been granted in the MMEL, the associated cooling fan may be inoperative without restrictions.

FAA Differences:  FAA relief is similar to TCCA.

ITEM:  21-60-1  CREW REST FACILITY - BUNK

System and Sequence No. Item Repair
Interval
Category
Number
Installed
Number
required
for
dispatch
Procedures
required
Remarks or Exceptions
Crew Rest Facility - Bunk Environmental Control System

1) Temperature Control

C 1 0 (M)

May be inoperative provided:

a) Heater is deactivated, and

b) Associated crew rest facility is not occupied.

2) Ventilation

C 1 0 (M)

May be inoperative provided:

a) Heater is deactivated,

b) Supply/boost fan is deactivated, and

c) Associated crew rest facility is not occupied.

3) Temperature Indicator

D 1 0    

DISCUSSION:

References:  AWM 525.831(e)(2)

This item addresses the air conditioning aspects of the crew rest facility - bunk.  Aircraft certification requirements must be considered when developing MMEL relief in this area.

FAA Differences: No FAA guidance currently available.

Date modified: