Data
from the "black box" flight recorders retrieved from the wreckage
suggests the pilots shut down one engine after the other lost power.
Earlier,
TransAsia said all of its pilots would be retaking proficiency examinations
following the disaster.
Fifteen
of the 58 people on board were rescued but at least 35 others died.
Thomas
Wang, executive director of Taiwan 's
Aviation Safety Council, said the plane's right engine triggered an alarm just
37 seconds after taking off from the Taipei 's
Songshan airport.
The
main pilot could be heard on black-box recordings saying the engine had
experienced a "flame-out", Mr Wang said, which can occur when the
fuel supply to the engine is interrupted.
However,
he said data showed that the engine had in fact been moved into idle mode.
Seconds later, the pilots
shut down the left engine, meaning neither engine was producing any power. A
restart was attempted, but the plane crashed 72 seconds later.
Officials
said it was unclear why the left engine had been turned off, especially as the
plane, an ATR 72-600, is able to fly with just one functioning engine.
Mr
Wang said it was too early to draw firm conclusions about why the first engine
had lost power but he told the BBC that the pilots had not followed normal
procedure.
"It's
only the third day so we can't say too much," he said. "We haven't
ruled anything out."
The flight, which had
been bound for Taiwan 's Kinmen Island ,
crashed into the Keelung
River .
A
more substantial report into the crash is expected to be released within the
next 30 days, ahead of the publication of a final report in the next three to
six months.
Pilot
praised
Earlier,
Taipei 's mayor
praised the main pilot, Liao Chien-tsung, for steering the plane away from
blocks of flats and commercial buildings before it came down.
Taiwanese
Vice-President Wu Den-yih also paid tribute to the 42-year-old pilot, saying he
had "meticulously
grasped" the flight controls in the plane's last few seconds.
"In
the final moments he still wanted to control the plane to avoid harming
residents in the housing communities," Mr Wu told reporters.
Crash investigators told
Taiwanese media that Mr Liao's hands were still on the plane's controls when
his body was found.
Both
the pilot and co-pilot were found dead in the cockpit, according to local media
reports.
The
BBC's Cindy Sui in Taipei
said search-and-rescue teams had been focusing their efforts downstream of the
crash site, and are carrying out operations along a 15-km (9-mile) stretch of
the river.
The
main parts of the plane, which had been submerged, have been retrieved from the
water.
Divers
are now attempting to locate the remaining victims and four more bodies were
retrieved from the water on Friday.