09/13/19
Message Overview:
Fault Message:
APU REVERSE FLOW
Fault Code:
4960136APU
Associated CAS:
| Reporting LRU: | Full-Authority Digital Engine-Controller (FADEC) |
| System Description: | 49-60-00 |
| Schematic Diagram: | 49-61-00 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Wiring Diagram: | 49-12-00 [ Global Express ] [ G5000 ] [ Global XRS ] 49-61-01 [ Global Express ] [ G5000 ] [ Global XRS ] |
Fault Description:
A reverse flow condition has occurred in Flight, when the Auxiliary Power Unit (APU) Inlet Temperature (T2) is more than 350°F (176.7°C) for five seconds.
| Fault | See * below | Description |
|---|---|---|
| FADEC FAILURE | ECU internal failure (CPU, watchdog timer, O/S circuit failure, loss of O/S protection, etc.) | |
| O/SPD | (Hardware/Software) overspeed circuits tripped (at 106%) | |
| LOSS OF SPEED | Both monopoles failed | |
| LOSS OF O/SPD | FADEC overspeed circuit/FCU fuel output solenoid failed | |
| OVERTEMP | * | EGT limit exceeded during i) start ii) on-speed operation |
| FIRE EMERG | * | Fire signal is received by the FADEC |
| REVERSE FLOW | * | T2 temp. limit (176.6°C/350°F) has been exceeded for 5 secs |
| HIGH OIL TEMP | * | Oil temp limit of >148.9°C exceeded for 10 seconds |
| LOW OIL PRESS | * | Oil pressure has fallen below lower limit of 30 psig for 15 seconds, with RPM > 95% |
| LOSS OF EGT DETECTION | * | Both EGT thermocouples have failed (NOTE: In Essential Mode, FADEC programs an EGT of 260°C to maintain the APU running) |
| NO FLAME | EGT rise has not been detected within 17 seconds of fuel solenoid being commanded open by FADEC or RPM >18% for 5 seconds | |
| NO ACCEL | Acceleration is < 0.05% of the prescheduled rate (normal acceleration is 2.5% per seconds) | |
| SLOW SPEED | Starter timer expired-APU RPM > 5% and less than starter cut out for 30 seconds | |
| UNDER SPEED | * | Speed has reached 100%, drops below 80% for 5 secs |
| NO CRANK | RPM does not rise above 5% within: i) 2 secs. when oil temp is warmer than minus 23°C ii) 50 secs. when oil temp is minus 23°C or lower |
|
| INLET DOOR | Inlet door position indicates closed 30 secs before starter engagement or 600 msecs. after starter engagement | |
| LOSS OF DC POWER | Loss of 28 VDC power for 200 milliseconds | |
| LOP SW FAIL | * | Oil pressure switch has failed open when RPM is < 7% (NOTE: This switch is normally closed during prestart BITE) |
| FALLBACK | APU drop below 25% RPM after starter cutout | |
| APU GCU HIGH OIL TEMP | * | APU Generator oil temperature above 215°C |
| NOTE: An asterisk mark (*) in any row above means that the automatic protection shut-down on that row is inhibited if the associated fault occurs in flight. The respective CAS message or an advisory message reading APU FAULT will be displayed in the CAS window and the APU will not shut-down automatically in flight. However the pilot may select to shut-down the APU manually by placing the APU control switch to OFF. | ||
Possible Causes:
- Auxiliary Power Unit (APU) Surge Valve (MPE2)
- Bleed Air Check Valve
- Tail Cone
- Load Control Valve (LCV) (MPE1)
- Full-Authority Digital Engine-Controller (FADEC) (A108)
- Sensor (T2)
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin: None
Forum Articles/Infoservice/Newsletter: None
If CAS message is not active, verify stored faults on CAIMS.
Quick Links:
| Access to Stored Faults | AMM 45-45-00-970-803 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Removal of the Engine Branched Wiring-Harness | AMM 49-12-01-000-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Installation of the Engine Branched Wiring-Harness | AMM 49-12-01-400-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Removal of the Bleed Air Duct | AMM 49-16-01-000-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Installation of the Bleed Air Duct | AMM 49-16-01-400-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Removal of the Surge Valve | AMM 49-51-01-000-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Installation of the Surge Valve | AMM 49-51-01-400-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Removal of the Load Control Valve | AMM 49-52-05-000-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Installation of the Load Control Valve | AMM 49-52-05-400-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Removal of the Bleed-Air Check Valve | AMM 49-52-09-000-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Installation of the Bleed-Air Check Valve | AMM 49-52-09-400-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Removal of the Full-Authority Digital Engine-Controller (FADEC) | AMM 49-61-01-000-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Installation of the Full-Authority Digital Engine-Controller (FADEC) | AMM 49-61-01-400-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Wire Repair - Maintenance Practices - ALL | SPM 20-12-10-02 [ Global Express ] [ G5000 ] [ Global XRS ] |
Troubleshooting Recommendations:
- Inspect the wiring and connectors on the APU for any damage, repair or replace as required.
- Check T2 temperature in CAIMS (CAIMS path: SYSTEM DIAG/49-00 APU/FADEC/LRU TEST/APU DATA STATUS-PAGE 1). T2 temperature above 176.7 will post the CAS message and shut down the APU. Make sure that the temperature is decreasing.
- If temperature does not decrease, check that the resistance changes on the probe itself (disconnected from harness) and do close out.
- If system checks good, troubleshoot the harness or FADEC and continue with next step.
- Examine the APU and the area around the APU for signs of fire.
- Verify surge control valve is in the open position, replace as required.
- Check that the bleed air check valve is not stuck in the closed position, repair or replace as required.
- Check that the load control valve is in the closed position.
- If load control valve is in closed position, go to step 8.
- If load control valve is in open position, continue with next step.
- Replace load control valve.
- If system checks are good, do close out.
- If fault remains, continue with next step.
- Replace FADEC.
- Do close out.