The ATSB is advising operators of single-engine Pratt & Whitney Canada PT6A powered aircraft to train pilots for uncommanded engine acceleration malfunctions, after 10 people were injured in a charter flight accident involving a Cessna Caravan on Far North Queensland's Lizard Island last year.
On 8 January 2024, the East Air-operated aircraft took off from Lizard Island for a planned flight to Cairns, with a pilot and nine passengers on board, an ATSB investigation report details.
During the climb, the pilot heard a change in the engine and noted that the aircraft was accelerating. The gauges showed engine torque and temperature above the redline, and no indications for gas generator speed or fuel flow. Propeller revolutions were high but within the normal operating range.
The pilot elected to return to land at Lizard Island. However, the uncontrollable excessive engine power led to a high‑speed approach, and the aircraft touching down long on the short runway.
The pilot applied maximum braking, but the aircraft overran the end of the runway at 92 kt and continued across undulating sandy soil, and low vegetation, until its left wingtip struck the ground.
The aircraft spun, flipped, and came to rest inverted, 127 m from the runway end. All ten occupants sustained minor injuries.
"The ATSB investigation concluded the uncommanded engine acceleration was likely due to a malfunction of the engine's fuel control unit," ATSB Director Transport Safety Kerri Hughes said.
Data provided by engine manufacturer Pratt & Whitney Canada indicated uncommanded engine acceleration events historically occurred more often than 'roll back to idle' malfunctions.
"Pilots of PT6A turbine single engine aircraft are trained for 'roll back to idle' malfunctions, but not trained for uncommanded engine acceleration malfunctions," Ms Hughes said.
"Consequently, as demonstrated in this accident, there is limited awareness by pilots and operators of how to safely respond to an uncommanded engine acceleration event in aircraft powered by PT6A engines."
Subsequently, the ATSB has issued a safety advisory notice to single-engine PT6A-powered aircraft operators, encouraging them to consider the potential responses to an uncommanded engine acceleration malfunction for different phases of flight, to document appropriate actions, and to train pilots for such scenarios.
"ATSB consultation with Cessna Caravan training organisations found that there was limited awareness of this type of event," Ms Hughes said.
"While not as immediately dire as an engine failure or roll back to idle, an uncommanded engine acceleration is alarming and requires prompt action to control the aircraft and prevent overstress of the engine and airframe."
Ms Hughes acknowledged changes made by the operator of the accident aircraft including publishing a temporary revision to its Quick Reference Handbook for the Cessna 208B to include an emergency item for unscheduled power increase during flight.
"When faced with non‑normal or emergency scenarios for which there are no procedures, pilots are required to exercise judgement based on their experience, skills and knowledge," Ms Hughes noted.
"Operators should consider updating their procedures and providing appropriate training to ensure that their pilots are adequately prepared for such events."
You can find here the final report: Engine malfunction and runway overrun involving Cessna 208B, VH‑NWJ, Lizard Island Airport, Queensland, on 8 January 2024
You can find here the SAN: Uncommanded engine acceleration events on single-engine PT6A powered aircraft
