Taipei: One of the two engines on TransAsia Airways Flight 235 went idle 37 seconds after takeoff, and the pilots apparently shut off the other before making a futile attempt to restart it, Taiwan's top aviation safety official said.
It was unclear why the second engine was shut down, since the plane was capable of flying with one engine. Taiwan's official China News Agency said investigators were looking into the possibility of "professional error."
Wednesday's crash into a river in Taipei minutes after takeoff killed at least 36 people and left seven missing.
Fifteen people were rescued with injuries after the accident, which was captured in a dramatic dashboard camera video that showed the ATR 72 propjet banking steeply and scraping a highway overpass before it hurtled into the Keelung River.
There would be no reason to have shut down the good engine, experts said.
"It's a mistake," said John M Cox, a former US Airways pilot and now head of a safety-consulting company. "There are procedures that pilots go through safeguards when you're going to shut down an engine, particularly close to the ground. Why that didn't occur here, I don't know."
Multi-engine planes, whether jets or turboprops like the ATR, are designed to fly on one engine. When an engine quits, one technique that pilots often use, Cox said, is to identify and tell each other which engine is still running, then for one of them to place a hand behind the throttle controlling that good engine —guarding against an accidental shutdown.
Cox said it is too early to draw certain conclusions but it's likely that the crew's failure to control the plane and shutting down the operating engine "will be part of the causal factors to this accident."
The details on the engines were presented at a news conference in Taipei by Aviation Safety Council Executive Director Thomas Wang as preliminary findings from the flight data recorder.
Wang said the plane's right engine triggered an alarm 37 seconds after takeoff. However, he said the data showed it had not shut down, or "flamed out" as the pilot told the control tower, but rather moved into idle mode, with no change in the oil pressure.
Then, 46 seconds later, the left engine was shut down, apparently by one of the pilots, so that neither engine was producing any power. A restart was attempted, but the plane crashed just 72 seconds later.
Several Internet aviation sites, including Flightradar24, questioned whether the pilots may have mistakenly turned off the wrong engine in an attempt to restart the idled one.