Intermittent autopilot disconnects in a Cirrus SR22 glass cockpit can be a challenging problem, often stemming from a few key areas: pilot input, faulty servo motors, or issues within the avionics system itself. A pilot’s inadvertent interaction with the controls or trim can cause an automatic disconnect, while a deteriorating servo or a glitch in a component like the AHRS can be the root of a hardware-related failure. ✈️
Pilot-Induced Disconnects
Often, an intermittent autopilot disconnect is not a malfunction but a safety feature working as designed. The GFC 700 autopilot in the SR22 is very sensitive to pilot input.
- Trim Usage: Simply touching or “bumping” the electric pitch trim switch while the autopilot is engaged will cause it to disconnect.
- Control Yoke Input: Applying even slight pressure to the control yoke against the autopilot’s command can be enough to trigger a disconnect. The autopilot will automatically disconnect if the forces on the servos exceed a certain level, indicating that the pilot is trying to override it.
- Out-of-Trim Condition: While the autopilot has an auto-trim function, it can struggle to maintain a commanded attitude in an aircraft that is significantly out of trim. This can cause the servos to work harder, potentially leading to a disconnect. The autopilot may flash trim indicators, prompting the pilot to manually trim the aircraft to relieve the servo pressure.
Autopilot Servo and Hardware Issues
If the disconnect is not pilot-induced, the problem likely lies in the autopilot’s mechanical and electrical components. The servos are the “muscles” of the autopilot, and they are prone to wear and tear.
- Servo Motor Issues: The autopilot servo motors can wear out over time. A servo may require a higher voltage to start moving, which can trigger a disconnect. A qualified technician can perform a voltage test to check the health of the servo and ensure it’s functioning within the manufacturer’s specifications. Common servo issues include clutch failures or motor brush deterioration.
- System Component Failures: The autopilot system relies on data from various other avionics components, such as the Attitude and Heading Reference System (AHRS) and the Air Data Computer (ADC). An intermittent failure or “mis-compare” in one of these units can cause the autopilot to disconnect. For example, if the AHRS reports an unexpected attitude, the system may decide to disengage as a safety measure. An avionics technician can troubleshoot these components by checking for error codes in the system’s logs.
The Aero Center’s Approach to Autopilot Repair
Troubleshooting an intermittent autopilot disconnect requires a specialized and methodical approach, often involving a ground run-up and, if necessary, a functional check flight to replicate the issue. At The Aero Center, we have a reputation for successfully diagnosing these complex problems. Our technicians are experienced in working with the integrated Garmin G1000 and GFC 700 systems in the Cirrus SR22.
As the only 24/7 maintenance center in the California, Arizona, and Nevada region, we understand the importance of minimizing aircraft downtime. We use our expertise and specialized diagnostic tools to pinpoint the exact cause of the disconnect, whether it’s a worn servo, a software glitch, or a wiring issue. Our goal is to provide a reliable and long-lasting solution, ensuring your aircraft’s autopilot system operates with the precision and safety you expect.
Footnotes:
- https://www.aopa.org/training-and-safety/air-safety-institute/accident-analysis/featured-accidents/autopilot-mishap-kills-two
- https://www.cirruspilots.org/Publications/Articles/autopilot-troubleshooting
- https://www.savvyaviation.com/grounded-by-glass/
- https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/19_phak_ch17.pdf
The Aero Center is located at William J. Fox Airfield KWJF | Lancaster, CA. Contact us at 209.885.6950 for questions or appointments. Sources