08/08/24
Message Overview:
| DDG Reference: | 22-10-00 |
| Pilot Action (QRH): | AVNC 02-3 |
| System Description: | 22-11-00 |
| Schematic Diagram: | None |
| Wiring Diagram: | None |
Message Description:
The amber 'AP HOLDING NOSE DOWN' caution CAS message indicates the Autopilot pitch servo is holding control force on the Nose Down.
- The pitch servo is drawing excessive current to maintain a pitch to command or there is no feed back from the servo tach after position change commanded.
- Check control freedom of movement, servo and servo clutch / mount for possible binding and servo tach feed back wiring to IAPS FGC.
- The pitch servo control system will re-position the horizontal stabilizer in the direction to reduce servo command force, assure the stabilizer system is working with the autopilot pitch system, or that the amber AP STAB TRIM FAIL message isn't associated with this message.
Possible Causes:
- Aileron Servo (A126)
- Servo Clutch
- Integrated Avionics Processor System (IAPS) (A4)
- Flight Guidance Computer (FGC) (A4-FGC)
- Associated Wiring
Troubleshooting Tips:
Advisory Wire/Service Bulletin:
- AW300-22-0372 - Autopilot Troubleshooting Data
- AW300-27-0409 - Autopilot (AP) Trim Airplane Flight Manual (AFM) Procedures
Forum Articles/Infoservice/Newsletter: None
Quick Links:
| Removal of the Flight Guidance Computer (FGC) | AMM 22-11-01-000-801 |
| Installation of the Flight Guidance Computer (FGC) | AMM 22-11-01-400-801 |
| Removal of the Aileron Servo | AMM 22-11-17-000-801 |
| Installation of the Aileron Servo | AMM 22-11-17-400-801 |
| Operational Test of the Aileron Servo | AMM 22-11-17-710-801 |
| Removal of the Elevator Servo | AMM 22-11-21-000-801 |
| Installation of the Elevator Servo | AMM 22-11-21-400-801 |
| Operational Test of the Elevator Servo | AMM 22-11-21-710-801 |
| Functional Test of the Elevator Cable Tension | AMM 27-31-00-720-801 |
| Functional Test of the Elevator Control System | AMM 27-31-00-720-802 |
| Rigging of the Elevator Control Cables | AMM 27-31-00-820-801 |
| Operational Test of the Pitch Trim System | AMM 27-41-00-710-801 |
| Functional Test of the Pitch Trim System | AMM 27-41-00-720-801 |
| Electrical Rigging of the Pitch Trim System | AMM 27-41-00-820-801 |
| Rigging Check of the Pitch Trim System | AMM 27-41-00-220-801 |
| Wiring - Maintenance Practices - ALL | SPM 20-12-00-02 |
| Wire Repair - Maintenance Practices - ALL | SPM 20-12-10-02 |
Troubleshooting Recommendations:
- Check control freedom of movement, servo and servo clutch / mount for possible binding and servo tach feed back wiring to IAPS FCC per AMM TASK 27-31-00-710-801. Verify the cable system tension & rigging per AMM TASK 27-31-00-820-801.
- Verify the Stab Trim system is functioning properly IAW TASK 27-41-00-720-801.
- Check the servo motor for proper operation IAW AMM TASK 22-11-21-710-801, pay particular attention to the movement of the elevator motor when driven with the heading bug. The motor should drive the controls to the stop fully and not be easily overridden. An SVO Test procedure can be done, this is not a permanent fix, however may temporary fix an issue where the servo motor after prolonged usage may have a "dead spot" in the tach/motor position.
To identify the aircraft flying characteristics, it is recommended under full fuel (8,500 lbs), the following worksheet is filled out Aileron Trim & Control Worksheet, email the worksheet in to the Montreal CRC for possible SRPSA disposition.
