An ROC Aviation Corp plane that crashed in central Taiwan last week had increased its altitude and hit trees at two separate locations before it crash landed, a preliminary investigation by the Aviation Safety Council into the cause of the deadly accident has found.
The information came to light on Wednesday after the council decoded the data recorded on the plane’s aerial photographic equipment and compared that with the data retrieved from the radar system.
Aviation Safety Council Executive Director Thomas Wang (王興中) said the decoded information showed that the Britton-Norman islander BN-2 took off from the Taipei International Airport (Songshan) at 7:26am on Thursday.
It then requested to stop using instrument flight rules and go by visual rules after it arrived in a mountainous area between Yilan and Hualien that was to be photographed.
Wang said the aircraft disappeared from radar screens at 9:16am. The decoded information showed it had maintained its altitude at between 2,500m and 2,600m.
“When the aerial assignment ended at 9:20:55am, the aircraft began to increase its altitude from 2,500m at a speed of 120 nautical miles [222km],” Wang said. “However, the speed dropped to 70 nautical miles at 9:22:33am. The last recorded altitude was 2,917m.”
“Why did the pilots decide to raise the aircraft’s altitude before it dropped? Why did the aircraft crash in the spot at which it was found? We need further analyses of the recorded information [to answer those questions],” Wang said.
The radar systems in both Hualien and Taitung could not detect the aircraft because the plane had flown into a blind spot of the radar system, which is blocked by the high mountains, he said.
Wang said the aircraft hit trees in two separate locations.
He said investigators found remains of the aircraft’s left wing on trees in one location near the site of the plane crash and those of the tail wing at another, nearby, location.
Wang said that the council is scheduled to dispatch another group of investigators to the crash site on Saturday to bring back more equipment for investigation, including the plane’s engines and the dashboard.
The details of the council’s investigation will be published online within three months, Wang said, but it will be about a year before the council delivers its comprehensive report into the accident.