Pre-conditioning through the LP Ground Connection (Aircraft Electrical Power Not Available)

TASK 12-33-21-618-001-A-03
Pre-conditioning through the LP Ground Connection (Aircraft Electrical Power Not Available)

WARNING: MAKE SURE THAT DURING THIS PROCEDURE THE AIRCRAFT IS IN ONE OF THESE THREE CONDITIONS:

THE CABIN PRESSURE OUTFLOW VALVE IS OPEN.
THE FWD AVIONICS COMPARTMENT ACCESS DOOR 811 IS OPEN.
ONE OR MORE PASSENGER DOORS ARE OPEN.

YOU MUST ATTACH A WARNING NOTICE TO THE OPEN DOORS TO TELL PERSONS NOT TO CLOSE THEM. THIS PREVENTS ACCIDENTAL PRESSURIZATION OF THE AIRCRAFT.

CAUTION: MAKE SURE THAT:

THE OUTLET TEMPERATURE OF THE GROUND AIR SUPPLY UNIT IS MINIMUM 2.0 DEG. C (35.6 DEG. F)
THE STATIC PRESSURE AT THE AIRCRAFT CONNECTOR IS LESS THAN 40 MBAR (0.58 PSI).

IF THE VALUES ARE NOT IN THESE LIMITS, DAMAGE TO THE AIR CONDITIONING SYSTEM CAN OCCUR.

CAUTION: DO NOT USE CONDITIONED AIR FROM THE APU OR HIGH-PRESSURE GROUND UNIT AT THE SAME TIME AS AIR FROM THE LOW-PRESSURE GROUND UNIT. IF YOU DO NOT OBEY THIS PRECAUTION, DAMAGE TO THE CHECK VALVES OR THE AIRCRAFT CAN OCCUR.

CAUTION: MAKE SURE THAT THE GROUND AIR-SUPPLY UNIT IS NOT TOO NEAR THE AIRCRAFT AND THAT THE ENGINE EXHAUST PIPE OF THE GROUND AIR- SUPPLY UNIT POINTS AWAY FROM THE AIRCRAFT. HEAT FROM THIS UNIT AND FROM THE EXHAUST CAN CAUSE DAMAGE TO THE AIRCRAFT STRUCTURE.

ZONE: 121
ZONE: 191

1. Reason for the Job
There are alternative methods for the pre-conditioning. This task is used during maintenance with the aircraft electrical power not available. For the other methods, refer to the related tasks in this page block.
2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment

REFERENCE	QTY	DESIGNATION
No specific	1	ACCESS PLATFORM 2M (6 FT)
No specific	1	GROUND AIR-SUPPLY UNIT(LOW PRESSURE)
No specific	AR	WARNING NOTICE(S)

B. Work Zones and Access Panels

ZONE/ACCESS	ZONE DESCRIPTION
121	AVIONICS COMPARTMENT
191	AIR CONDITIONING COMPT AND FAIRINGS
191CB, 811

C. Referenced Information

REFERENCE	DESIGNATION
TASK 52-41-00-010-002-A	Open the Avionics Compartment Doors for Access
TASK 52-41-00-410-002-A	Close the Avionics Compartment Doors after Access
LP and HP Ground Connectors

3. Job Set-up
Subtask 12-33-21-010-063-A

A. Get Access
(1) Open access door 191CB.
(2) Connect the GROUND AIR-SUPPLY UNIT(LOW PRESSURE) to the aircraft LP connector.

Subtask 12-33-21-941-058-A

B. Safety Precautions
(1) Do one of the safety precautions that follow:
(a) Make sure that forward-avionics-compartment access door 811 is in good condition and in the open position:
1 Put the ACCESS PLATFORM 2M (6 FT) in position below forward-avionics-compartment access door 811.
2 Open forward-avionics-compartment access door 811 (Ref. AMM TASK 52-41-00-010-002).
(b) Make sure that a minimum of one passenger/crew door is in good condition and in the open position:
1 Put the WARNING NOTICE(S) in position to tell persons not to close the passenger/crew door.

4. Procedure
Subtask 12-33-21-618-071-A

A. Pre-conditioning through the LP Ground Connection (Aircraft Electrical Power Not Available)
(1) Obey the instructions given in the ground-air supply unit.
(2) Start the ground air-supply unit, and make sure that:
(a) The airflow is not more than 78 kg.min (171.96 lb.min).
(b) The supplied air pressure is not more than 40 mbar (0.58 psi) at the aircraft interface connector.
(3) Set the necessary output air temperature on the GROUND AIR-SUPPLY UNIT(LOW PRESSURE), and make sure that:
(a) The supplied air temperature does not increase to more than 70 deg.C (158.00 deg.F).
(b) The supplied air temperature does not decrease to less than 2 deg.C (35.60 deg.F).
(4) When the pre-conditioning is not necessary, stop the GROUND AIR-SUPPLY UNIT(LOW PRESSURE):
(a) Obey the instructions given in the ground-air supply unit.

5. Close-up
Subtask 12-33-21-410-061-A

A. Close Access
(1) Disconnect and remove the GROUND AIR-SUPPLY UNIT(LOW PRESSURE) from the aircraft LP connector.
(2) Close access door 191CB.
(3) If opened, close forward-avionics-compartment access door 811 (Ref. AMM TASK 52-41-00-410-002).
(4) Remove the WARNING NOTICE(S).
(5) Remove the ground support and maintenance equipment, the special and standard tools and all other items.
(6) If opened, close the passenger/crew door.

[Rev.10 from 2021] 2026.04.02 06:10:37 UTC