APU AUTO SHUTDOWN - UNDERSPEED, APU is unable to hold Speed (131-9(A))

TASK 49-00-81-810-805-A
APU AUTO SHUTDOWN - UNDERSPEED, APU is unable to hold Speed (131-9(A))

1. Possible Causes

NO LRU DETECTED
blockage of the APU inlet
damage/leakage of the APU FUEL SYSTEM
aircraft fuel-line of the APU-pump fuel-system.
APU FUEL FILTER
APU internal dammage
FUEL CONTROL UNIT (P19)
APU INLET PRESSURE TRANSDUCER (P22)
SPEED SENSORS (P26)
APU INLET TEMPERATURE SENSOR (P6)
ELECTRONIC CONTROL BOX [59KD]
APU [4005KM]
FUEL CONTROL UNIT (8022KM)
APU INLET PRESSURE TRANSDUCER (8048KM)
SPEED SENSORS (8060KM)
APU INLET TEMPERATURE SENSOR (8010KM)

2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment

REFERENCE	QTY	DESIGNATION
No specific	AR	WRENCH - RATCHET
No specific	AR	WRENCH - SOCKET

B. Referenced Information

REFERENCE	DESIGNATION
AMM 28-22-00-710-001	Operational Test of the APU Fuel-Pump System on Ground to Purge the Fuel Line
AMM 49-00-00-860-008	APU Start by External Power
AMM 49-11-11-000-004	Removal of the Power Plant (APU) (131-9(A))
AMM 49-11-11-400-004	Installation of the Power Plant (APU) (131-9(A))
AMM 49-23-14-000-001	Removal of the Sensor-APU Inlet Temperature (131-9(A))
AMM 49-23-14-400-001	Installation of the Sensor-APU Inlet Temperature (131-9(A))
AMM 49-32-11-000-003	Removal of the Fuel Control Unit (FCU) (131-9(A))
AMM 49-32-11-400-003	Installation of the Fuel Control Unit (FCU) (131-9(A))
AMM 49-32-41-920-001	Replacement of the Fuel Filter (131-9(A))
AMM 49-51-21-000-001	Removal of the Transducer - APU Inlet Pressure (131-9(A))
AMM 49-51-21-400-001	Installation of the Transducer - APU Inlet Pressure (131-9(A))
AMM 49-61-34-000-003	Removal of the Electronic Control Box (ECB) (131-9(A))
AMM 49-61-34-400-003	Installation of the Electronic Control Box (ECB) (131-9(A))
AMM 49-71-13-000-003	Removal of the Speed Sensors (131-9(A))
AMM 49-71-13-400-003	Installation of the Speed Sensors (131-9(A))
AMM 49-91-42-200-004	Inspection of the Metal Chip Detector (131-9(A))

3. Fault Confirmation
Subtask 49-00-81-710-104-A ** ON A/C NOT FOR ALL

A. Read-out of ECB Trouble-Shooting Data
(1) Put the APU MASTER SW to the ON position.
(2) Get access to the APU SHUTDOWN report.
(3) Push the '>' adjacent to LRU DATA:

the MCDU menu shows
NO LRU DETECTED

(4) Start the APU and apply Bleed Air for 20 seconds, minimum AMM 49-00-00-860-008.

4. Fault Isolation
Subtask 49-00-81-810-083-A ** ON A/C NOT FOR ALL

A. If an APU auto shutdown occurs during the APU operation and the APU SHUTDOWN report gives the maintenance message:

UNDERSPEED
FCU/APU FUEL SUPPLY/APU ROTATION

associated with Fault Code Number (FCN) 204

do a check for a blockage of the APU inlet

(1) If the fault continues:

do a check for damage/leakage of the APU FUEL SYSTEM.

(a) If there is damage/leakage in the APU FUEL SYSTEM:

do a repair.

(b) If the APU FUEL SYSTEM is OK:

purge the aircraft fuel-line of the APU-pump fuel-system. AMM 28-22-00-710-001.

1 If the fault continues:

replace the APU FUEL FILTER AMM 49-32-41-920-001.

2 If the fault continues:

do a check for APU internal dammage :
- do check for contamination of the MAGNETIC-DRAIN PLUG AMM 49-91-42-200-004.

NOTE: If the MAGNETIC-DRAIN PLUG is not contaminated, continue without starting the APU

.
- remove the end cap from the STARTER MOTOR (8KA).
- use a WRENCH - SOCKET and a WRENCH - RATCHET on the shaft of the STARTER MOTOR (8KA) to turn the APU counterclockwise (in the direction of the arrow on the housing).
- make sure that the APU rotates freely.

a If the APU does not rotate freely:

replace the APU (4005KM) AMM 49-11-11-000-004 and AMM 49-11-11-400-004.

b If the APU rotates freely:

replace the FUEL CONTROL UNIT (P19) AMM 49-32-11-000-003 and AMM 49-32-11-400-003.

c If the fault continues:

replace the APU INLET PRESSURE TRANSDUCER (P22) AMM 49-51-21-000-001 and AMM 49-51-21-400-001.

d If the fault continues:

replace the SPEED SENSORS (P26) AMM 49-71-13-000-003 and AMM 49-71-13-400-003.

e If the fault continues:

replace the APU INLET TEMPERATURE SENSOR (P6) AMM 49-23-14-000-001 and AMM 49-23-14-400-001.

f If the fault continues:

replace the ELECTRONIC CONTROL BOX [59KD] AMM 49-61-34-000-003 and AMM 49-61-34-400-003.

g If the fault continues:

replace the APU [4005KM] AMM 49-11-11-000-004 and AMM 49-11-11-400-004.

Subtask 49-00-81-810-083-B ** ON A/C NOT FOR ALL

A. If an APU auto shutdown occurs during the APU operation and the APU SHUTDOWN report gives the maintenance message:

UNDERSPEED
FCU (8022KM) / APU FUEL SUPPLY / APU ROTATION

associated with Fault Code Number (FCN) 204

do a check for a blockage of the APU inlet