Failure of the HCU Pressurizing Valve on the Engine 2

TASK 78-31-00-810-858-A
Failure of the HCU Pressurizing Valve on the Engine 2

1. Possible Causes

PRESS SW-HCU [4102KS]
HCU-THRUST REV (4101KS)
ECU [4000KS]

2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
AMM 73-21-60-000-001	Removal of the Electronic Control Unit (ECU)
AMM 73-21-60-400-001	Installation of the Electronic Control Unit (ECU)
AMM 78-31-00-710-040	Operational Test of the Thrust Reverser System
AMM 78-31-00-710-042	Operational Test of the Thrust Reverser System
AMM 78-31-16-000-040	Removal of the Hydraulic Control Unit Pressure Switch
AMM 78-31-16-000-041	Removal of the Hydraulic Control Unit Pressure Switch
AMM 78-31-16-400-040	Installation of the Hydraulic Control Unit Pressure Switch
AMM 78-31-16-400-041	Installation of the Hydraulic Control Unit Pressure Switch
AMM 78-31-51-000-040	Removal of the Hydraulic Control Unit
AMM 78-31-51-000-042	Removal of the Hydraulic Control Unit
AMM 78-31-51-400-040	Installation of the Hydraulic Control Unit
AMM 78-31-51-400-042	Installation of the Hydraulic Control Unit

3. Fault Confirmation
Subtask 78-31-00-710-168-B ** ON A/C NOT FOR ALL

A. Test
(1) Do the operational test of the thrust reverser system (MENU mode test) AMM 78-31-00-710-040.

Subtask 78-31-00-710-168-C ** ON A/C NOT FOR ALL

A. Test
(1) Do the operational test of the thrust reverser system (MENU mode test) AMM 78-31-00-710-042.

4. Fault Isolation
Subtask 78-31-00-810-117-B ** ON A/C NOT FOR ALL

A. The fault message is generated if a position fault is detected on the HCU pressurizing valve (valve detected open when reverse stowage is commanded). The HCU pressurizing valve position monitoring is based upon the output signal of the HCU pressure switch. The warning ENG 2 REV PRESSURIZED is generated only if the fault has persisted for more than 10 seconds:

switch closed = no pressure,
switch opened = valve pressurized.

(1) If the test gives the maintenance message HCU (TRPV), OPEN and the thrust reverser blocker doors deploy and stow normally:

replace the PRESS SW-HCU [4102KS] AMM 78-31-16-000-040 and AMM 78-31-16-400-040.

(a) If the fault continues:

replace the ECU (4000KS) AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(2) If the test gives the maintenance message HCU (TRPV), OPEN and the thrust reverser blocker doors do not deploy or stow normally:

replace the HCU-THRUST REV (4101KS) AMM 78-31-51-000-040 and AMM 78-31-51-400-040.

(a) If the fault continues:

replace the ECU [4000KS] AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(3) If the test does not give the maintenance message HCU (TPRV), OPEN:

replace the HCU (4101KS) AMM 78-31-51-000-040 and AMM 78-31-51-400-040.

(a) If the fault continues:

replace the ECU (4000KS) AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

Subtask 78-31-00-810-117-C ** ON A/C NOT FOR ALL

switch closed = no pressure,
switch opened = valve pressurized.

(1) If the test gives the maintenance message HCU (TRPV), OPEN and the thrust reverser blocker doors deploy and stow normally:

replace the PRESS SW-HCU [4102KS] AMM 78-31-16-000-041 and AMM 78-31-16-400-041.

(a) If the fault continues:

replace the ECU (4000KS) AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(2) If the test gives the maintenance message HCU (TRPV), OPEN and the thrust reverser blocker doors do not deploy or stow normally:

replace the HCU-THRUST REV (4101KS) AMM 78-31-51-000-042 and AMM 78-31-51-400-042.

(a) If the fault continues:

replace the ECU [4000KS] AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

(3) If the test does not give the maintenance message HCU (TPRV), OPEN:

replace the HCU (4101KS) AMM 78-31-51-000-042 and AMM 78-31-51-400-042.

(a) If the fault continues:

replace the ECU (4000KS) AMM 73-21-60-000-001 and AMM 73-21-60-400-001.

Subtask 78-31-00-710-169-B ** ON A/C NOT FOR ALL

B. Do the test given in Para. 3.A.
(1) No additional maintenance action is required if the fault is not confirmed.
(2) Repeat the fault isolation procedure if the fault continues.

[Rev.8 from Aug 2018] 2026.04.04 04:38:04 UTC