The Full-Authority Digital Engine-Controller (FADEC) commanded an Auxiliary Power Unit (APU) shut down, or failure to start, because the FADEC received a signal from the inlet door Rotary Variable Differential Transducer (RVDT) that was out of the expected range.

• Inlet-Door Rotary Transducer (MT5)
• Auxiliary Power Unit (APU) Full-Authority Digital Engine-Controller (FADEC) (A108)
• Associated Wiring

Advisory Wire/Service Bulletin: None

Forum Articles/Infoservice/Newsletter: None

If CAS message is not active, verify stored faults on CAIMS.

1. Access CAIMS and using active faults or stored faults, find the fault and verify the CAS message. You can use System Diagnostics to view each channel of the APU FADEC (each sensor) in real time, and also access ground faults. Page 2 of the APU DATA STATUS shows the APU inlet door position.
2. Verify Visually that the APU inlet door is accurate to the CAIMS readings.
3. Inspect the wiring and connectors to the inlet-door rotary transducer for any damage.

   1. If damages are found, repair as required and do close out.
   2. If damages are not found, continue with next step.

4. Inspect the transducer (RVDT) for condition and perform continuity check on transducer connector (P804) as follows:

   From	To	Expected Result	Result
   P804-2	P804-3	<1000 ohms

   1. If the resistance check is not as mentioned above, repair defective wiring as required and do close out.
   2. If the resistance check is as mentioned above, continue with next step.

5. Perform continuity check between the transducer connector (P804) and grounded shell as follows:

   From	To	Expected Result	Result
   P804-2	Ground	>1 megaohm
   P804-6	Ground	>1 megaohm

   1. If the resistance check is not as mentioned above, replace defective inlet door rotary transducer and do close out.
   2. If the resistance check is as mentioned above, continue with next step.

6. Perform a voltage check within J804 as follows:

   From	To	Expected Result	Result
   J804-2(-)	J804-3(+)	5 ±1.5 volts

   1. If voltage checks are not good, repair defective wiring as required and do close out.
   2. If voltage checks are good, continue with next step.

7. Re-rack FADEC and verify connector A108AP1-A7 and A108AP1-B7 for damage or FOD.

   1. If damages are found, repair as required and do close out.
   2. If damages are not found, continue with next step.

8. Perform wiring checks between APU FADEC connector (A108AP1) and the transducer connector J804.

   1. If wiring checks are not good, repair defective wiring as required and do close out.
   2. If wiring checks are good, continue with next step.

9. Replace the APU FADEC.
10. Do close out.