Taipei, Aug. 1 (CNA) A sudden drop in engine efficiency and a flight deviation were recorded in the black boxes of the TransAsia Airways plane that crashed in the outlying county of Penghu July 23, but the cause remains under investigation, the Aviation Safety Council said Friday.

The revolutions of one of the turboprop's two engines dropped suddenly when the pilots requested a go-around at 7:06 p.m. on the day of the crash, the council said.

About the same time, the black boxes recorded unusual sounds that the council said could be a result of a smash between the turboprop and a wooded area close to the island county's Magong Airport.

The cause of the abnormal engine activity remains unknown, said council managing director Wang Hsing-chung, adding however that tree branches were found in one of the engines of the plane.

In addition, the path of Flight GE222 deviated from normal before the pilots started to operate the flight manually instead of automatically in preparation for landing, Wang said at a press briefing.

When the pilots turned off automatic operation of the plane at 7:05 p.m., the flight had sheered 13 degrees counterclockwise from its designated angle, he said.

According to the black boxes, the pilots did not mention any abnormal conditions during the flight, although they did comment on the strong winds as they approached the airport at around 6:45 p.m.

TransAsia flight GE 222, which took off from Kaohsiung on the evening of July 23, crashed after aborting a landing in inclement weather and attempting go-arounds.

Forty-eight of the 58 people onboard were killed in the crash. A preliminary report on the crash will be filed with both the Executive Yuan and the International Civil Aviation Organization by the end of August, according to Wang.

However, a complete report will not be available for 18 months, he said.

(By Lee Hsin-Yin)
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●Aug. 1: Flight GE222 recorded two unusual sounds just before crash: officials