09/21/21
Message Overview:
Message Name:
APU NO START
| Message Code: | 496OBS003 |
| Effectivity: | All |
| System: | Auxiliary Power Unit (APU) Automatic Control System |
| System Description: | 49-60-00 |
| Schematic Diagram: | 49-61-00 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Wiring Diagram: | 49-61-01 [ Global Express ] [ G5000 ] [ Global XRS ] |
Message Description:
The Auxiliary Power Unit (APU) fails to start completely.
Possible Causes:
- Auxiliary Power Unit (APU) Full-Authority Digital Engine-Controller (FADEC) (A108)
- Starter Motor (B55)
- Starter Brushes
- Ignition Unit (A2)
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin:
- AW700-49-0334 - APU STARTER-Brush Inspection
- AW700-49-0538 - Auxiliary Power Unit (APU) Exhaust Gas Temperature (EGT) Sensor
Forum Articles/Infoservice/Newsletter:
- Honeywell Sil APU-99 - Electronic Control Unit (ECU) "No Fault Found" Removals
- Honeywell Sil APU-137 - AIRBORNE AUXILIARY POWER-GAS TURBINE ENGINE-Introduction of a field cleaning procedure for the RE220 APU starter PN: 2704554
Quick Links:
| APU Safety Precautions | AMM 49-00-00-910-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Removal of the Ignition Exciter | AMM 49-41-01-000-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Installation of the Ignition Exciter | AMM 49-41-01-400-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Removal of the Starter Motor | AMM 49-42-01-000-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Installation of the Starter Motor | AMM 49-42-01-400-801 [ Global Express ] [ G5000 ] [ Global XRS ] |
| Cleaning of the Starter Motor of Brush Dust Material | AMM 49-42-01-110-801 [ 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:
- If APU RPM increases normally up top 45% on Ground (starter disconnects at 45% on ground) and/or 60% in Flight (starter disconnects at 60% in flight) and EGT rises but then hangs and drops down, perform a Combustor wash, inspect both igniters and ignition leads.
- During the attempted start, does the APU RPM value increase and "hang" at a level below 50% RPM before the start is aborted?
- If NO, go to step 6.
- If YES, continue with next step.
- Remove the APU FADEC (A108) and disconnect the Ignition Unit connector (A2P1). Perform a continuity check as follows:
From To Result A108BP1-111 A2P1-2 A108BP1-112 A2P1-29 - If there is no continuity, repair defective wiring as required and do close out.
- If there is continuity, continue with next step.
- Perform a continuity check as follows:
From To Result A108BP1-111 Ground A108BP1-112 Ground - If there is continuity, repair defective wiring as required and do close out.
- If there is no continuity, continue with next step.
- Replace the Ignition Unit (A2). Is the fault still present?
- If NO, do close out.
- If YES, continue with next step.
- Measure the resistance across the starter terminals with an ohmmeter while manually rotating the starter with the HAND CRANK ACCESS.
- If resistance is less than 1000 ohms, go to step 8.
- If resistance is more than 1000 ohms, continue with next step.
- Clean the Starter Brushes. Is the fault still present?
- If NO, do close out.
- If YES, continue with next step.
- Replace the Starter Motor.
- Do close out.