TransAsia pilots undergo mandatory proficiency tests following crash that kills at least 36

In this photo taken Thursday, Feb. 5, 2015, emergency personnel inspect of one of the recovered engines at the site of a commercial plane crash in Taipei, Taiwan. 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. The Taiwanese commercial flight with 58 people aboard clipped a bridge shortly after takeoff and crashed into a river in the island's capital of Taipei on Wednesday morning. (AP Photo/Wally Santana) (The Associated Press)

In this photo taken Thursday, Feb. 5, 2015, relatives pray for victims in front of one of the recovered engines at the site of a commercial plane crash in Taipei, Taiwan. 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. The Taiwanese commercial flight with 58 people aboard clipped a bridge shortly after takeoff and crashed into a river in the island's capital of Taipei on Wednesday morning. (AP Photo/Wally Santana) (The Associated Press)

A ground mechanic works on the engine area of a TransAsia Airways ATR airplane at the Songshan Airport in Taipei, Taiwan, Saturday, Feb. 7, 2015. All 71 pilots who operate the airline's ATR propeller-jets began proficiency tests on Saturday, three days after one of the carrier's ATRs crashed into a river. (AP Photo/Wally Santana) (The Associated Press)

TransAsia Airways says that all 71 of its ATR pilots have begun proficiency tests after one of the airline's propeller-jets crashed into a river this past week, killing at least 36 people.

The airline said Saturday it has canceled 90 flights in the next three days to accommodate the requirement by the Civil Aeronautics Administration that its ATR pilots be retested.

Preliminary investigations indicate the pilots of Wednesday's doomed flight shut off a running engine of the ATR 72 after its other engine went idle, and aviation experts say the move could have been a mistake.

Local prosecutors have said they would be looking into the possibility of "professional error."

The Civil Aeronautics Administration said Saturday morning that seven people from the 58 on board remained missing. Fifteen people survived.