# SDR 2026FA0000634

- Type: Service difficulty report (as reported; unverified)
- Difficulty date: December 20, 2025
- Submitted: August 10, 2026
- Operation: General aviation
- Aircraft: [N3486N](https://openairdocs.org/aircraft/N3486N), registered now
- Make and model: Mooney M20F
- Registry model: [Mooney M20F](https://openairdocs.org/model/mooney-m20f) (OpenAirDocs)
- Aircraft serial: 680068
- Aircraft time: 5,670 hours
- Engine: Lyc AEIO360A1A
- System (JASC): [2210 · Autopilot System](https://openairdocs.org/jasc/2210)
- Part: Servo
- Part number: 006B162608
- Part serial: 5G9013449
- Condition: Failed
- Location: Zone 100
- Stage of operation: DE
- How discovered: O
- Nature of condition: J, F
- Precautionary procedure: A
- FAA source: FAA Service Difficulty Reporting System (https://sdrs.faa.gov/)
- Page: https://openairdocs.org/sdr/2026FA0000634

## Discrepancy

DURING DESCENT FROM BIG BEAR, THE GARMIN AUTOPILOT ABRUPTLY DISCONNECTED FOLLOWING FAILURE OF THE GSA 28 PITCH SERVO. IMMEDIATELY PRIOR TO THE FAILURE, I OBSERVED A MOMENTARY PITCH-TRIM-DOWN INDICATION. THE AIRCRAFT USES MANUAL PITCH TRIM. UPON SERVO/AUTOPILOT DISCONNECT, THE AIRCRAFT PITCHED UP AGGRESSIVELY AND AIRSPEED DECAYED RAPIDLY. IMMEDIATE AND SUBSTANTIAL FORWARD CONTROL INPUT WAS REQUIRED TO LOWER THE NOSE, RECOVER AIRSPEED, AND MAINTAIN AIRCRAFT CONTROL. THE FAILED GSA 28 WAS WITHIN THE POPULATION IDENTIFIED BY GARMIN IN A SERVICE BULLETIN ADDRESSING POTENTIAL SERVO FAILURES. REPLACEMENT WAS RECOMMENDED BUT NOT MANDATORY. REPLACEMENT ULTIMATELY COST APPROXIMATELY $2,500. I AM CONCERNED THAT THE FINANCIAL AND LABOR BURDEN ASSOCIATED WITH CORRECTING A KNOWN SAFETY-RELATED FAILURE MODE MAY DISCOURAGE COMPLIANCE WITH A VOLUNTARY SERVICE BULLETIN, LEAVING AFFECTED SERVOS IN SERVICE UNTIL FAILURE.     GIVEN THE SIGNIFICANT FLIGHT-CONTROL UPSET RESULTING FROM THIS FAILURE, I RECOMMEND FAA REVIEW OF WHETHER VOLUNTARY CORRECTIVE ACTION PROVIDES ADEQUATE MITIGATION OR WHETHER MANDATORY CORRECTIVE ACTION IS WARRANTED.

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