Message Name:

S/D-NO LIGHTOFF

Message Code:

B3-006350

Associated CAS:

APU SHUTDOWN
(Advisory)

Auxiliary Power Unit (APU) protective shutdown - no light-off.

Advisory Wire/Service Bulletin: None

Full Throttle Blog/Forum Articles/Infoservice/Newsletter: None

Flight Operation Notifications Manual (FONM): None

1. Make sure there is proper fuel flow to the APU:
   During the Starting the Auxiliary Power Unit (APU) AMM 49-11-00-866-801, confirm the following:

   • On the pilot Cursor Control Panel (CCP), push the FUEL button.
   • On the FUEL synoptic page  make sure that the R BOOST PUMP is turned ON (outline is green).
   • APU SOV shows OPEN.
   • APU flow line shows a GREEN line to the APU.

   1. If YES, continue with next step
   2. If NO, troubleshoot the fuel system.

2. Perform a wiring check between the APU ECU and the Ignition unit as follows:
   

   From APU ECU	To Ignition Unit	Result
   A39CP1-2	A173P1-B
   A39CP1-4	A173P1-A

   1. If wiring defects are found, repair defective wiring as required and do close out.
   2. If no wiring defects are found, continue with next step.

3. Perform a wiring check between the Ignition unit and the igniter plugs.
4. Inspect the Ignition leads/plugs for damage. Replace if necessary.
5. Perform a wiring check between the APU ECU and the Low Oil Pressure (LOP) Switch.
   

   From APU ECU	To Low Oil Pressure Switch	Result
   A39AP1-12A	S110P1-A
   A39AP1-5D	S110P1-B

   1. If wiring defects are found, repair defective wiring as required and do close out.
   2. If no wiring defects are found, continue with next step.

6. Replace the LOP switch.
7. Do close out.