Aviation safety issues and actions

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

Issue number: AO-2015-105-SI-01
Who it affects: Aircraft owners and operators of aircraft fitted with the Garmin G1000 avionics system and GFC700 autopilot.
Issue owner: Cessna Aircraft Company (Textron)
Transport function: Aviation: General aviation
Background: Investigation Report AO-2015-105
Issue release date: 17 April 2018
Current issue status: Partially addressed
Issue status justification:

The proposed safety action will increase pilot awareness for those pilots with access to the Pilot Safety and Warning Supplements. However, the ATSB believes that wider dissemination of the issue is possible. For that reason, while the ATSB recommendation will be closed, it is considered only partially 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 the safety issue by Cessna Aircraft Company

The functionality described is true of virtually every autopilot [fitted to FAR 23 certified aircraft]. The type of autopilot behavior being discussed is covered in chapter 4 of the Federal Aviation Administration’s Advanced Avionics Handbook (FAA-H-8083-6, attached). The first page of the chapter discusses autopilot concepts and in the “How to use an autopilot function,” says, “Allow the FD/autopilot to accomplish the modes selected and programmed without interference, or disengage the unit.  Do not attempt to “help” the autopilot perform a task. In some instances, this has caused the autopilot to falsely sense adverse conditions and trim to the limit to accomplish its tasking.  In more than a few events, this has resulted in a total loss of control and a crash.”

ATSB comment/action in response

Knowledge is imparted in a number of ways, which include reading operating manuals, conducting training, communicating with experienced pilots and learning from one’s own experiences.

Advanced avionics and autopilot systems are now fitted to a significant number of primary training aircraft, such as the Cessna 172S (VH-ZEW). The level of knowledge that individual pilots have in this environment starts at a low base level and builds over time. The ATSB contends that student pilots are not likely to be aware of issues surrounding manual manipulation of the flight controls with the autopilot on. It is therefore important to implement methods that enhance pilots’ awareness of the issue, including aircraft and avionics systems operating manuals having the requisite limitations, cautions and warnings in place.

It is clear from the content of the FAA handbook that they believe a warning about the issue is required. Although the handbook provides very good educational material, it does not take the place of aircraft operating manuals as a reference guide.

The G1000 avionics and GFC700 autopilot systems are fitted to numerous aircraft types. Some flight manuals include limitations, cautions and warnings and some do not. Additionally, there were no audible warnings provided for mistrim to enhance pilot awareness in the G1000 avionics system with the GFC 700 autopilot fitted, despite that being a feature of the superseded autopilot system.

As a result, the ATSB has released the following safety recommendation.

Recommendation

Action number: AO-2015-105-SR-004
Action organisation: Cessna Aircraft Company (Textron)
Date: 17 April 2018
Action status: Closed

ATSB safety recommendation Cessna Aircraft Company (Textron)

The ATSB recommends that Cessna Aircraft Company, in conjunction with Garmin, implement changes to their operations manuals so that all aircraft types fitted with their autopilots have the limitations, cautions and warnings applied consistently.

Additional correspondence

Response date: 26 July 2018
Response from: Cessna Aircraft Company
Action status: Closed
Response text:

In response to the issued safety recommendation, Textron Aviation issued a revision to the Pilot Safety and Warning Supplement that is provided with every Cessna aircraft propeller product Owner’s Manual and Pilot’s Operating Handbook. The Supplement is also available through the manufacturer’s Customer Service website. The revised document contained a section on Autopilots and Electric Trim Systems that included a warning that overriding an engaged autopilot system will cause the trim system to oppose the pilot’s input and result in an out of trim condition.

ATSB comment:

The ATSB recognises the safety action that Textron (Cessna Aircraft Company) has implemented to improve pilot awareness of the issues relating to the manual manipulation of the flight controls with the autopilot on. However, the Pilot Safety and Warning Supplements will not be readily available to vast majority of Cessna pilots’ who have not purchased a new aircraft or requested a new supplement.

Last update 25 February 2020