A Cessna 210 forced landing accident that followed a partial power loss due to the engine mixture probably not being set to full rich highlights the importance of pilots familiarising themselves with aircraft systems and the operational environment, and a well-structured take-off safety brief.
The single piston-engine Cessna 210L was being used for a charter flight from Groote Eylandt to Ngkurr, Northern Territory, on 16 June 2023 when, shortly after becoming airborne, the pilot reported the engine began to surge, and there were fuel flow fluctuations.
During the attempted turn back and landing, the aircraft passed diagonally over the runway then touched down beyond the airport boundary, in a clear grassed area.
The aircraft continued along the ground for about 120 m before hitting an embankment, flipping over, and coming to rest inverted on a mine service road.
Three passengers were seriously injured, while the other two passengers and pilot sustained minor injuries. The aircraft was substantially damaged.
An ATSB investigation concluded the reduced power and unanticipated engine behaviour was probably the result of the mixture control, which controls the ratio of fuel to air entering the engine cylinders, not being set to full rich prior to take-off. This meant that during the take-off roll when full throttle was applied, there was a disproportionately low fuel component of the air-fuel ratio, reducing engine power output, resulting in the partial power loss and unanticipated engine behaviour.
"The pilot was likely surprised by the partial power loss, which was compounded by their limited experience of flying the Cessna 210, and took no action to resolve the situation, and did not effectively manage the attempted landing," Director Transport Safety Dr Stuart Godley said.
"Notably, the ATSB found the pilot's take-off safety self-brief, and the aircraft operator's documented example brief, did not detail actions to be taken in the event of a partial power loss."
Dr Godley noted the ATSB research publication Managing partial power loss after take-off in single engine aircraft provides detailed guidance on the risks of and managing partial power loss scenarios.
"Forward planning, such as a well-structured take-off safety brief, increases a pilot's situation awareness, reduces mental workload under stress, and increases the prospect of a safe and well-managed outcome in the event of an emergency," he said.
The investigation also noted that the risk of injuries to passengers in the aircraft was increased by the aircraft's rear seats not being fitted with upper torso restraints.
"Although any effect this had on the occupants' injuries in this accident could not be determined, the lack of upper torso restraints for rear passenger seats increases the likelihood of serious injury," Dr Godley said.
Regulations did not require the aircraft to have upper torso restraints for the rear passenger seats, and their lack of fitment and usage in older light aircraft is highlighted by the ATSB's SafetyWatch concern, reducing the severity of injuries in accidents involving small aircraft.
"Upper torso restraints can significantly reduce the risk of injury, compared to lap belts only, by minimising the flailing of the upper body and the potential of impacts involving the head and upper body," Dr Godley concluded.
