A Beechcraft Baron crashed at Cowra Airport in April this year after the crew attempted a go-around below the aircraft's minimum control speed, according to an ATSB investigation report published yesterday.
E55 VH-OMD was being flown on a dual IFR flight conducting an NDB approach to Cowra when the instructor cut the left engine by closing the mixture control. The pilot continued the approach with the left propeller windmilling.
During the landing flare, the instructor initiated a go-around, but on application of power, the aircraft yawed rapidly to the left and rolled almost inverted before hitting the ground in a near vertical, nose down attitude.
Both crew members sustained minor injuries, but the aircraft was heavily damaged.
ATSB investigators found that the go-around had been attempted whilst the aircraft was below its minimum control speed (Vmca), resulting in the loss of control that led to the crash.
Vmca is the minimum forward speed needed to control the aircraft when in asymmetric flight.
"The instructor moved the left engine mixture lever to idle cut-off to simulate an engine failure over the navigation aid," the ATSB investigators concluded, "and it was likely that they unintentionally did not subsequently move the lever to rich and ensure the engine was restarted and available for instant use, when attempting to set zero thrust on the downwind leg of the circuit.
"As a result, the instructor initiated a go-around below the minimum control speed, unaware the left engine was inoperative, resulting in an asymmetric loss of control."
"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 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.'"
The manufacturer’s procedure calls for setting zero thrust by moving the propeller pitch lever to the feather detent, and then setting the engine power to 12 inches MAP.
According to the ATSB report, the instructor thought they had set zero thrust either inbound or on downwind, and recalled asking the pilot if they wanted it set. However, the pilot said they prompted the instructor to set zero thrust on downwind.
The approach continued with the left engine shut down, but with the propeller still turning.
“Accidents as a result of engine malfunctions in twin-engine aeroplanes are rare, but often fatal," Macleod said. "As such, training to manage one engine inoperative flight is important but should not introduce unnecessary risks.
“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.”
Since the accident the training operator, Fly Oz, has amended its multi-engine training procedures to simulate engine failures by closing the throttle rather than the mixture at any altitude.
The full investigation report is on the ATSB website, and an animated video explaining the sequence of events can be watched on You Tube.