NT plane 'broke up in flight', kills two
Turbulence and speed caused by a storm may have contributed to an "in-flight breakup" of a light plane that crashed in the Northern Territory, killing two young Queensland pilots.
Darcy McCarter, 23 and Daniel Burrill, 33, were repatriating an indigenous man's body from Darwin to Elcho Island in October when their Cessna 210 lost its wings, ripped through bushland and crashed on a rural road 30km from the airport.
"Witnesses in the vicinity of Howard Springs saw the aircraft descend rapidly in a relatively flat attitude with a portion of each wing missing," a preliminary Australian Transport Safety Bureau report found.
Both pilots were secured in their seats prior to the vertical impact.
The report found witnesses spotted "very black" clouds forming over the rural area at the time of the accident on October 23, in typical early wet-season conditions for the Top End.
To avoid bad weather, the pilot diverted the plane right of the flight path shortly after take off, but the ATSB said the developing clouds may have produced "strong updrafts or downdrafts".
About 20 minutes after take off at 1.29pm, air traffic controllers noticed the aircraft turn abruptly to the left, while its speed fluctuated as it descended and climbed in altitude.
The charter plane accelerated to 150 knots in the final minute of the flight, above the manoeuvring speed of 118 knots, and when this occurs control inputs or turbulence can produce damaging wing loading.
"At airspeeds above about 145 knots, this loading can result in failure of the aircraft structure," the report noted.
The single-engine, six-seater aircraft disappeared from radar display twice before the fatal plunge.
Wreckage from the Air Frontier plane, which was more than 40 years old, was strewn either side of Gunn Point Road, with its wings and "severely impact-damaged" body found 740 metres apart.
"The wing spars had fractured in over-stress, and exhibited bending deformation consistent with forces acting upwards and rearwards on the wings," the ATSB said.
"The propeller did not exhibit any evidence of rotation at impact, consistent with fuel exhaustion resulting from the ruptured integral wing-fuel tanks."
The charter plane showed no pre-existing defects that could have contributed to the crash, maintenance inspections were up to date and there was no evidence of a fire.
The investigation will further examine electronic data, the effect of weather conditions on the flight and pilot experience before a final report is released.
All seven in-flight break-ups of Cessna 210 aircraft in the United States since 2000 have involved flight into thunderstorms or associated turbulence, a loss of control following inadvertent flight into meteorological conditions, or a combination of both.
© AAP 2017