04/26/21
Message Overview:
Message Description:
The nose of the aircraft trims down or trims up without any action from the crew. The autopilot is not active and there are no fault messages.
Possible Causes:
- Pilot Pitch/Roll/Arm Switch (S85)
- Copilot Pitch/Roll/Arm Switch (S84)
- Horizontal Stabilizer Trim Electronic Control Unit (HSTECU) (A130)
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin: None
Forum Articles/Infoservice/Newsletter: None
Quick Links:
| Removal of the Pitch/Roll Trim Switch | AMM 27-41-01-000-801 |
| Installation of the Pitch/Roll Trim Switch | AMM 27-41-01-400-801 |
| Removal of the Motor Control Unit (MCU) | AMM 27-41-13-000-801 |
| Installation of the Motor Control Unit (MCU) | AMM 27-41-13-400-801 |
| Removal of the Horizontal-Stabilizer-Trim Electronic-Control Unit (HST ECU) | AMM 27-41-21-000-801 |
| Installation of the Horizontal-Stabilizer-Trim Electronic-Control Unit (HST ECU) | AMM 27-41-21-400-801 |
| Wiring - Maintenance Practices - ALL | SPM 20-12-00-02 |
| Wire Repair - Maintenance Practices - ALL | SPM 20-12-10-02 |
| Electrical Connectors - Maintenance Practice - ALL | SPM 20-20-00-02 |
Troubleshooting Recommendations:
- Physically check the pilot and copilot Pitch Trim switches. Make sure they "click" properly in the nose down and nose up position and spring back to the neutral position.
- If the switch doesn't seem to operate properly, replace the switch.
- If no defects are found, continue with next step.
- Remove the HSTECU and access connector A130AP1 and A130BP1. Perform a continuity check as follows:
From To Result A130AP1-3B Ground A130AP1-3K Ground A130AP1-3A Ground A130AP1-3J Ground A130BP1-2B Ground A130BP1-2K Ground A130BP1-2A Ground A130BP1-2J Ground NOTE: While performing this step, make sure another person is moving and turning the control column back and forth in order to attempt to detect an intermittent connection inside the control column.
- If there is no continuity, continue with next step.
- If there is continuity, repair defective wiring as required and do close out.
- Access the Motor Control Unit connectors A131P3 and A131P4. Perform a continuity check as follows:
From To Result A130AP1-1H A131P4-14 A130AP1-1A A131P4-11 A130AP1-1B A131P4-10 A130AP1-1E A131P4-22 A130AP1-5K A131P3-15 A130AP1-5J A131P3-13 A130AP1-5H A131P3-14 A130AP1-5A A131P3-11 A130AP1-5B A131P3-10 A130AP1-5E A131P3-22 - If there is continuity, continue with next step.
- If there is no continuity, repair defective wiring as required.
- Perform a continuity check as follows:
From To Result A130AP1-1H Ground A130AP1-1A Ground A130AP1-1B Ground A130AP1-1E Ground A130AP1-5K Ground A130AP1-5J Ground A130AP1-5H Ground A130AP1-5A Ground A130AP1-5B Ground A130AP1-5E Ground - If there is continuity, repair defective wiring as required.
- If there is no continuity, continue with next step.
- Replace the HSTECU.
- Do close out.