A Baron that yawed and rolled before impacting the ground next to the runway after the mixture instead of the throttle had been used to simulate an engine failure highlights the importance of procedures aligning with manufacturer guidance.
On 11 April 2024, an instructor and student pilot were operating the twin-engine Beechcraft E55 Baron to conduct a navigation exercise under the instrument flight rules from Cowra, New South Wales, an ATSB investigation report details
After conducting instrument approaches to Goulburn and Canberra, the aircraft returned to Cowra to fly an instrument approach with one engine inoperative.
Arriving over the airport, the instructor simulated a single engine failure by moving the left engine mixture control lever to the idle cut-off position.
"This was in accordance with the operator's relevant procedure at the time, but differed from Beechcraft's aircraft flight manual," Director Transport Safety Stuart Macleod said.
The manufacturer's procedure prescribes setting zero thrust by retarding the propeller lever to the feather detent, and the throttle lever to 12 inches of manifold pressure.
"The Beechcraft flight manual states using the throttle to simulate engine failure is to 'avoid difficulties of restarting an engine and preserve the availability of engine power'," Mr Macleod noted.
Civil Aviation Safety Authority guidance also recommends using the throttle, and not mixture, for one engine inoperative training.
With the aircraft operating on just the right engine, and the left engine's propeller windmilling, the student conducted an instrument approach before visually establishing the aircraft on final approach to the runway.
During the landing flare, the instructor initiated a go-around, and the aircraft rapidly yawed and rolled to the left, impacting the ground in an almost vertical nose-down attitude, before coming to rest inverted.
Fortunately, the pilots survived with minor injuries, even though ATSB analysis found the impact deceleration likely exceeded 30 G, principally in a forward direction, with the stable collapse of the airframe structure forward of the cabin and crash-resistant fuel cells aiding their survivability.
"When attempting to set zero thrust during the downwind leg of the final circuit, it was likely the instructor unintentionally did not move the left engine's mixture lever back to rich, to ensure it was available for instant use if needed," Mr Macleod explained.
"As a result, the go-around was initiated below the minimum control speed, with the left engine inoperative, resulting in an asymmetric loss of control."
Since the accident the training operator, Fly Oz, has amended its multi-engine training procedures to only simulate engine failures using throttle at any height.
"Accidents as a result of engine malfunctions in twin-engine aeroplanes are rare, but often fatal. As such, training to manage one engine inoperative flight is important but should not introduce unnecessary risks," Mr Macleod remarked.
"In this case, the manufacturer required the throttle be used to simulate an engine failure, and CASA guidance also recommends using the throttle rather than the mixture. This ensures power can quickly be restored if needed."
