A light aircraft that crashed near Darwin in October, killing two pilots, disappeared from radar display twice before the fatal plunge, and transport authorities are investigating if airspeed and bad weather were factors.
Pilots Darcy McCarter, 23, and Daniel Burrill, 33, were on a training flight transporting the body of a man back to Elcho Island for a traditional Aboriginal burial when their six-seater single-propeller Cessna 210 crashed near Gunn Point Road about 25 minutes after take-off on October 23.
A preliminary report released by the Australian Transport Safety Bureau said witnesses saw the Air Frontier aircraft descend rapidly with a portion of each wing missing, and the examination of the wreckage, which was scattered over 810 metres, found it was consistent with an in-flight break-up, and that there was no evidence of fire.
“The main fuselage was found less than 1NM [one nautical mile] from the last recorded radar position and both aircraft wings were located about 700m south-east of that site,” the report said.
The report details how one of the pilots requested clearance to divert off course because of weather just a few minutes after they took off at 1:07pm.
“At the time of the accident, the pilots were deviating around some significant weather in the area and we believe this would have produced some significant forces at that time,” said ATSB spokesman Nat Nagy.
The report said that a thunderstorm to the north of Darwin, combined with the north-west sea breeze, triggered a connective cell to develop rapidly between 1:00pm and 1:30pm between Howard Springs and Koolpinyah, and the developing cumulus clouds “may have produced strong updrafts or downdrafts”.
The report stated that weather that day was typical of the Northern Territory’s early wet season, also known as “the build-up”, with unstable conditions, and showers and storms expected.
“Witnesses reported seeing a large cumulus cell form over the Howard Springs area, which they described as a regular occurrence in the build-up season in Darwin,” the report said.
“Some reported that the cloud went ‘very black’ at the time of the accident, and that starting about 10 minutes after the accident, it rained heavily for about an hour.”
Plane disappeared twice from radar
The plane also had to avoid nearby active restricted airspace and was diverted three times before recording a jump in groundspeed from 130 knots to 150 knots.
At 1:32pm while the plane was at 10,100 feet travelling at a groundspeed of 100 knots, “the aircraft altitude disappeared from radar display… the controllers immediately assessed the absence of this line as abnormal,” the report said.
About 10 seconds later, three short transmissions, likely from the aircraft’s radio, were recorded, and the aircraft’s altitude briefly reappeared at a lower reading of 5,100 feet with a groundspeed of 70 knots.
But 15 seconds later, the plane disappeared from the radar screen a second time.
“The controllers attempted to make radio contact with the pilot but were unsuccessful,” the report said.
The report noted that with airspeeds above manoeuvring speed of 118 knots, as specified by the aircraft’s manufacturer, “control inputs or turbulence may produce wing loading that can damage the aircraft’s structure”.
“At airspeeds above about 145 knots, this loading can result in failure of the aircraft structure,” it said.
“Our report at the moment does indicate that the aircraft was exceeding its manoeuvring speed and that is certainly one factor that we will be looking at,” Mr Nagy said.
The aircraft was not equipped with a flight data recorder or cockpit voice recorder, nor was it required to be, the report said.
A periodic inspection of the aircraft was completed on September 26, a month before the accident, and a scheduled 50-hourly inspection was completed the day of the crash.
The maintenance release reported there were no concerns with aircraft serviceability prior to its departure from Darwin Airport, and the pilots did not advise of any aircraft-related issues.
The report said the United States National Transportation Safety Board has investigated seven in-flight breakups of Cessna 210 aircraft since 2000.
“All involved flight into thunderstorms or associated turbulence, a loss of control following inadvertent flight into instrument meteorological conditions, or a combination of both,” it said.
The investigation is continuing and will include examination of the recovered plane components and available electronic data; weather conditions; pilot qualifications and experience; and the aircraft’s maintenance and operational records.
A final report is expected by the end of 2018.