Fuel - ACT Pressure is Incorrectly Released through the ACT Vent System

TASK 28-28-00-810-836-A
Fuel - ACT Pressure is Incorrectly Released through the ACT Vent System

WARNING: OBEY THE FUEL SAFETY PROCEDURES.

1. Possible Causes

VALVE-PRESSURE HOLDING, ACT (191QM)
OVER PRESSURE PROTECTOR (170QM)
VALVE-VENT, ACT (167QM)
vent-line couplings and pipe work

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 28-11-27-400-001	Installation of the Additional Center Tank (ACT)
AMM 28-11-37-000-001	Removal of the inner Manhole Cover ACT
AMM 28-11-37-400-001	Installation of the inner Manhole Cover ACT
AMM 28-12-55-000-001	Removal of the ACT Overpressure Protector (170QM)
AMM 28-12-55-400-001	Installation of the ACT Overpressure Protector (170QM)
AMM 28-28-35-000-001	Removal of the ACT Vent Shut-off Valve (167QM)
AMM 28-28-35-400-001	Installation of the ACT Vent Shut-off Valve (167QM)
AMM 28-28-48-000-001	Removal of the ACT Pressure Holding Valve
AMM 28-28-48-400-001	Installation of the ACT Pressure Holding Valve

3. Fault Confirmation
Subtask 28-28-00-710-072-A ** ON A/C NOT FOR ALL

A. Test
(1) There is no test for this ACT fault. If the applicable ACT:

moves fuel correctly, no more maintenance work is necessary
does not move fuel correctly, because the ACT pressure decreases through the aircraft vent system, do the fault isolation procedure in Para. 4.A.

4. Fault Isolation
Subtask 28-28-00-810-091-A ** ON A/C NOT FOR ALL

A. Procedure
(1) Remove the applicable ACT that does not move fuel correctly AMM 28-28-48-000-001.
(2) At the ACT:
(a) Remove the two manhole covers AMM 28-11-37-000-001.
(b) Cap all connectors on the vent-line, but keep open the bleed connector in the vent-line cover plate, on the front wall of the ACT.
(c) Make sure that the vent valve and the fuel inlet valve are closed.
(d) Make sure that the GROUND PRESSURE GENERATOR - 0.19 BAR (2.75 PSI) does not give more than 0.2 bar (2.9 psi).
(e) Use an Adaptor, ACC to AN814-4ADL, to connect the GPG to the bleed connector in the vent line cover plate, on the front wall of the ACT.
(f) Very slowly pressurize the vent-line to 0.2 bar (2.9 psi), to make sure that if the pressure-holding valve is open, it does not close. The pressure must not decrease.

NOTE: It is important to know if it is the pressure-holding valve that is the cause of the fault. If the pressure from the GPG is applied suddenly, it can close the valve and cause the fault to go, before it is identified.

(g) In the ACT, do a check for air-leakage into the tank-bladder, from the vent-line, at the:

VALVE-PRESSURE HOLDING, ACT (191QM)
OVER PRESSURE PROTECTOR (170QM)
VALVE-VENT, ACT (167QM)
vent-line couplings and pipe work .

(h) Disconnect the GPG from the vent-line bleed connector.
(3) From the air-leakage check in step (2)(g):
(a) If air-leakage is found, replace the unserviceable component:

for the VALVE-PRESSURE HOLDING, ACT (191QM) AMM 28-28-48-000-001 and AMM 28-28-48-400-001
for the OVER PRESSURE PROTECTOR (170QM) AMM 28-12-55-000-001 and AMM 28-12-55-400-001
for the VALVE-VENT, ACT (167QM) AMM 28-28-35-000-001 and AMM 28-28-35-400-001
for the vent-line couplings and pipe-work, replace as necessary.

(b) If air-leakage is not found, replace the VALVE-PRESSURE HOLDING, ACT (191QM) AMM 28-28-48-000-001 and AMM 28-28-48-400-001.
(4) Do the tests in steps (2)(e) thru (2)(h) again. If the fault:

stays, do step (3)(a)
goes, do the next step.

(5) At the ACT:
(a) Remove the caps from all the connectors on the vent-line.
(b) Install the two manhole covers AMM 28-11-37-400-001.
(6) Install the ACT AMM 28-11-27-400-001.
(7) Make a record in the aircraft logbook to do a check of the movement of fuel (auto transfer) from the applicable ACT, during the next flight.

[Rev.8 from Aug 2018] 2026.04.04 04:28:52 UTC