Aviation safety issues and actions

Autopilot advice, limitations cautions and warnings (written and audible)

Issue number: AO-2015-105-SI-02
Who it affects: Aircraft owners and operators of aircraft fitted with the Garmin G1000 avionics system and GFC700 autopilot.
Issue owner: Garmin
Transport function: Aviation: General aviation
Background: Investigation Report AO-2015-105
Issue release date: 17 April 2018
Current issue status: Not addressed
Issue status justification:

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.

Safety issue description

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.

Response to safety issue by Garmin

The avionics manufacturer indicated that since all autopilots work the same way, it was common knowledge for pilots not to manually manipulate the flight controls with the autopilot on. Therefore, any advice, limitations, or warnings about the issue would not be required. They also indicated that the presence of a limitation, warning, or caution is generally left up to the certifier of the equipment in the airplane [in this case Cessna].

ATSB comment/action in response

Advanced avionics systems and autopilots are now fitted to many aircraft used by relatively inexperienced pilots. Therefore it is important that every opportunity is taken to inform them of the potential danger posed by manual manipulation of the flight controls with the autopilot on.

Recommendation

Action number: AO-2015-105-SR-006
Action organisation: Garmin
Date: 15 January 2018
Action status: Closed

ATSB safety recommendation Garmin

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.

Additional correspondence

Response from: Garmin response
Action status: Closed
Response text:

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:

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.

ATSB comment:

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.

Last update 25 February 2020