ACT 1 - FLSCU-3 Channel LS5 - Low Level Sensor No. 2 Failure

TASK 28-46-00-810-829-A
ACT 1 - FLSCU-3 Channel LS5 - Low Level Sensor No. 2 Failure

WARNING: OBEY THE FUEL SAFETY PROCEDURES.

WARNING: WHEN YOU DO WORK ON THE FUEL SYSTEM WIRING, YOU MUST USE TEST EQUIPMENT THAT IS APPROVED (REFER TO INTERNATIONAL OR NATIONAL SPECIFICATIONS FOR INTRINSICALLY SAFE TEST EQUIPMENT: EN50020, UL913 OR EQUIVALENT). TEST EQUIPMENT THAT IS NOT APPROVED CAN CAUSE FIRE OR AN EXPLOSION.

1. Possible Causes

FLSCU 3 [47QJ]
aircraft wiring
C/B-ACT LOW LVL R [51QJ]
PROBE-FQI NO 2, ACT1 [66QT1]

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

REFERENCE	QTY	DESIGNATION
No specific	AR	MULTIMETER - STANDARD

B. Referenced Information

REFERENCE	DESIGNATION
AMM 12-11-28-650-003	Pressure Refuel with Automatic Control
AMM 28-25-00-869-001	Fuel Transfer
ASM 282803
AMM 28-42-24-000-001	Removal of the Fuel Quantity Probe of the ACT
AMM 28-42-24-400-001	Installation of the Fuel Quantity Probe of the ACT
ASM 284602
AMM 28-46-34-000-001	Removal of the Fuel-Level Sensing Control-Unit (FLSCU)
AMM 28-46-34-400-001	Installation of the Fuel-Level Sensing Control-Unit (FLSCU)

3. Fault Confirmation
Subtask 28-46-00-865-077-A ** ON A/C NOT FOR ALL

A. Table of the circuit breakers referred to in this procedure:

PANEL	DESIGNATION	FIN	LOCATION
** ON A/C NOT FOR ALL
121VU	ACT LOW LVL R	51QJ	M29

Subtask 28-46-00-710-060-A ** ON A/C NOT FOR ALL

B. Test
FLSCU-3 (47QJ), CHAN LS5 - LO LVL SENSOR No. 2 (66QT1) Input To RELAY-PANEL (802VU) Fault Confirmation

NOTE: The ACT Low Level sensors are not FQIC BITE tested, manually tested or monitored by the FQIC during normal operation.

NOTE: OPTIONAL TESTING:
Where a PSDA321-1 Test Set is available, a check can be made before a decision is made to go into or close up a fuel tank. The Test Set lets a GO/NOGO check be made of the tank mounted components and wiring from the tank wall connectors.

(1) Examine the FUEL System Display ACT 1 FQ, and make sure it contains more than 250 kg (560 lb):

refuel the ACT 1 AMM 12-11-28-650-003 if necessary.

NOTE: This is to make sure the low level sensor is wet.
The fuel quantity/level at which the low level sensor changes state/operates is approximately 80 kg (180 lb) with the aircraft in a level attitude.

(2) Disconnect the free connector 4065VC-A from the RELAY-PANEL (802VU).
(3) Use a MULTIMETER - STANDARD, to do a test for continuity, at the free connector 4065VC-A between the pins <A and <B. This test must show an open circuit. If the test shows continuity, do the fault isolation procedure in Para. 4.A.
(4) Defuel the ACT 1 AMM 28-25-00-869-001.

NOTE: This is to make sure the low level sensor is dry.

(5) Use a multimeter, to do a test for continuity, at the free connector 4065VC-A between the pins <A and <B. This test must show continuity.
(6) If the test results are:
(a) As specified in steps (3) and (5):
1 No more FLSCU-3 (47QJ) Channel LS5 - Low Level Sensor No. 2 (66QT1) Trouble-shooting steps are necessary.
2 Connect the free connector 4065VC-A to the RELAY-PANEL (802VU).
(b) Not as specified in steps (3) and (5):

go to Para. 4. and do the fault isolation.

4. Fault Isolation
Subtask 28-46-00-810-078-A ** ON A/C NOT FOR ALL

A. Procedure
(1) Examine the C/B-ACT PROBE LO LVL RIGHT (51QJ) and make a note if it is open or closed.
(2) If the C/B 51QJ is closed:

go to Step (4).

(3) If the C/B 51QJ is open:
(a) Do a visual check of the items that follow and repair if necessary:
1 C/B 51QJ.
2 FLSCU-3 (47QJ).
3 FLSCU-3 rack connector (47QJ-A).
(b) Close the C/B 51QJ.
(c) Do the test given in Para. 3.B.
(4) Interchange the FLSCU-3 (47QJ) with FLSCU-1 (7QJ) AMM 28-46-34-000-001 and AMM 28-46-34-400-001.
(5) Do the test given in Para. 3.B.
(a) If the test is satisfactory:
1 Install the original FLSCU-1 in the FLSCU-1 position.
2 Replace the FLSCU 3 [47QJ] AMM 28-46-34-000-001 and AMM 28-46-34-400-001.
(b) If the fault continues:

install the FLSCUs in their original positions AMM 28-46-34-000-001 and AMM 28-46-34-400-001.

(6) Test Equipment

(a) If there is:

approved test equipment available, go to Step (7)
no approved test equipment available, go to Step (8).

(7) Do a resistance check ASM 284602 of the low level sensor (part of PROBE-FQI No 2, ACT 1 (66QT1) at the tank wall connector 66QT1-A (803VU) between pins D and E.

NOTE: The sensor status (wet or dry) and fuel/air temperature will have an effect on the resistance value.

(a) If the resistance is between 330 and 480 ohms:

go to Step (8).

(b) If the resistance is not between 330 and 480 ohms:

go to Step (15).

(8) Do a check of the aircraft wiring ASM 284602 and ASM 282803 between:

the FLSCU-3 rack connector AB, pin 8A and the ACT to tank break connector 7618VC1, pin 9 (sensor input line - H)
the FLSCU-3 rack connector AB, pin 8B and the ACT to tank break connector 7618VC1, pin 10 (sensor input line - L)
the ACT aircraft to tank break free connector 7618VC1-A, pin 9 and the tank unit free connector 66QT1-A, pin E (sensor input line - H)
the ACT aircraft to tank break free connector 7618VC1-A, pin 10 and the tank unit free connector 66QT1-A, pin D (sensor input line - L)
the FLSCU-3 rack connector AA, pin 10B and the RELAY-PANEL (802VU) free connector 4065VC, pin <B (LS5 channel input line from RELAY-PNL 802VU)
the FLSCU-3 rack connector AA, pin 9B and the RELAY-PANEL (802VU) free connector 4065VC, pin <A (LS5 channel output line to RELAY-PNL 802VU).

(9) Repair all the unserviceable wiring and connectors.
(10) Do the test given in Para. 3.B.
(11) If the fault continues:

remove the FLSCU-3 (47QJ) AMM 28-46-34-000-001.

(12) Do a test, with a MULTIMETER - STANDARD, to make sure that 28VDC is available at the FLSCU-3 (47QJ) rack connector AA, pin 1C.
(13) If the 28VDC is available:
(a) Install the FLSCU-3 (47QJ) AMM 28-46-34-400-001.
(b) Go to Step (15).
(14) If the 28VDC is not available:
(a) Do a check of and replace if necessary the C/B-ACT LOW LVL R [51QJ] .
(b) Do a check of the aircraft wiring ASM 284602:

between the C/B-ACT PROBE LO LVL RIGHT (51QJ), terminal 2 and the FLSCU-3 rack connector AA, pin 1C (28VDC supply line).

(c) Repair all the unserviceable wiring and connectors.
(d) Install the FLSCU-3 (47QJ) AMM 28-46-34-400-001.
(e) Do the test given in Para. 3.B.
(15) If the fault continues:

replace the PROBE-FQI NO 2, ACT1 [66QT1] AMM 28-42-24-000-001 and AMM 28-42-24-400-001.

[Rev.8 from Aug 2018] 2026.04.04 04:39:44 UTC