The lack of manufacturer written advice, limitations, cautions, or warnings (written or aural) about autopilot response to manual pilot control inputs meant that pilots may be unaware that their actions can lead to significant out of trim situations, and associated aircraft control issues.
The Garmin G1000 system with the GFC700 autopilot react the same way in every aircraft type they are fitted to. Therefore, Garmin is best placed to mitigate the risks involved in the ATSB identified safety issue. Consequently, the ATSB recommendation will be closed and assessed as not adequately addressed.
The ATSB recommends that Garmin, in conjunction with aircraft manufacturers, takes action to ensure that all aircraft types fitted with their autopilots have the limitations, cautions and warnings documented in the aircraft’s operating manuals. Further, the ATSB recommends that Garmin consider the use of audible warnings to enhance pilots’ awareness of mistrim situations brought on by the autopilot system.
A summary of the Garmin response is as follows:
Garmin did not conduct the certification of the autopilot system fitted to the Cessna 172S, nor did it contribute to the Airplane Flight Manual or its supplements (AFMS). Cessna was solely responsible for creating and maintaining the AFMS. Garmin has no ability to impose warnings or limitations in Cessna AFMS, nor would it be able to make changes or revisions.
When Garmin does conduct an autopilot certification via a Supplemental Type Certificate process, it does include warnings such as those mentioned in the ATSB report. An example of this is the Diamond DA40 that was certified in 2007 which included this warning:
DO NOT ATTEMPT TO MANUALLY FLY THE AIRPLANE WITH THE AUTOPILOT ENGAGED. THE AUTOPILOT SERVOS WILL OPPOSE PILOT INPUT AND WILL TRIM OPPOSITE THE DIRECTION OF PILOT INPUT (PITCH AXIS ONLY). THIS COULD LEAD TO A SIGNIFICANT OUT-OF-TRIM CONDITION. DISCONNECT THE AUTOPILOT IF MANUAL CONTROL IS DESIRED.
Garmin certified for the Cessna 182 in that same year and it included a similar warning as above. Every autopilot that has been certified through Garmin since has a similar warning in place in the AFMS.
As for aural warnings related to mistrim, these have been considered, and rejected by most avionics and aircraft manufacturers. It is unlikely that Garmin will include aural autopilot mistrim warnings in the future.
It is clear based on Garmin’s response that they have recognised the safety benefit of appropriate warnings in the AFMS of the products that they certify during the aircraft type certification process.
Although Garmin indicate that they did not have an input into the Cessna 172S AFMS, they do produce their own detailed guidance material which forms a part of the aircraft document suite. Specifically, the Garmin G1000 Intergrated Flight Deck Cockpit Reference Guide. The guide covers all of the Cessna Nav III product line which is inclusive of the newer Cessna 172’s, 182’s and 206 aircraft. Amongst other things, the guide has detailed information about the operation of the Garmin GFC700 autopilot, including helpful warnings, cautions and notes. However, it does not contain any information about issues surrounding manual flight with the autopilot engaged.
The ATSB contends that along with the AFMS, the G1000 pilots guide would be the appropriate place to add additional information about the dangers of manual manipulation of the flight controls with the autopilot on. This would ensure that there would be some information about the issue in each of the many aircraft types where the Garmin G1000 / GFC700 system is fitted.