Within two weeks business aircraft operating under US Federal Aviation Administration Part 25 rules must be compliant with a rule requiring their automatic flight guidance systems (FGS) to be more intuitive for pilots to operate and more benign if they fail.

This new regulation, which comes into force on 11 May, also simplifies the guidance to manufacturers about FGS performance requirements. The rule has been developed with the European Aviation Safety Agency (EASA), the FAA says, bringing the added benefit of transatlantic rule harmonisation.

The accidents and incidents cited by the US National Transportation Safety Board as the reason for changing requirements for FGSs – which include autopilots, autothrottles and flight management systems (FMS) – all happened to large transport aircraft, but the FAA says these have been upgraded voluntarily in advance of the ruling, so the remaining requirement for compliance has devolved on Part 25 business jet operators and FGS manufacturers for aircraft in that category.

The most serious accident cited was the April 1994 Airbus A300 crash at Nagoya, Japan, when the pilots became confused during an approach as to whether the autopilot was engaged or not, the pilot’s manual control inputs were counteracted by the autopilot, and the aircraft went out of control during an attempted go-around.

There have been no business jet FGS-related crashes, the FAA says, but there have been four incidents involving “autopilot disconnect and/or improper pilot procedures that could just as easily have been accidents”.

Without design mitigation, increasing FGS complexity and integration could make the situation worse, the FAA says.

The rule demands simplicity of operation and clarity of the selected FGS mode, says the FAA. For example: engagement or disengagement of any part of the system should be simple for either pilot and any transient attitude-change effects during engagement or disengagement should be design-limited, even in the case of failure.

FGS selected modes should also be clearly displayed, the FAA says.

Source: Flight International