A faulty connector about the size of a credit card helped trigger a series of mechanical and human failures that led to the crash of a 20-ton aircraft in February, killing 43 people, investigators in Taiwan found.
Microscopic tests of a soldered connector joint on the TransAsia Airways Corp. plane engine showed potential cracking, and the connector failed post-crash tests, the Aviation Safety Council said in a report today.
That failure is at the heart of why the ATR72 twin-propeller plane incorrectly sounded a cockpit warning and an engine adjustment known as autofeather. That set in motion a series of pilot errors that eventually crashed the aircraft into a downtown Taipei river Feb. 4.
“It did not send the correct signal,” Thomas Wang, the safety council’s executive director, told Bloomberg after a news conference in Taipei.
The pilots were incorrectly warned of an engine failure in the number 2 engine. They exacerbated the problem by mistakenly shutting down the other engine, which was functioning normally.
The pilot announced he would shut down engine 1, even though the screen in the cockpit was displaying a flameout in engine 2, Wang said.
“He called it wrong,” Wang said.
Less than three minutes after Flight GE235 took off from Taipei’s downtown Songshan airport, the 20-ton plane was lying partially submerged in a nearby river. Only 15 people survived the accident, TransAsia’s second crash in a year.
Even before the plane left the ground at 10:51 a.m., headed for Taiwan’s outlying Kinmen island, the two pilots noted signs of trouble.
“No ATPCS armed,” the co-pilot called out seconds after the plane began accelerating on the runway. He was referring to the Automatic Take-off Power Control System that automatically manages the ATR72’s engines in the event of a failure during take off.
“Ok, continue take off,” the pilot replied.
Eight seconds later, the co-pilot noted that the ATPCS was working.
Less than a minute later, with the plane at 1,200 feet, the master warning sounded, with a cockpit display listing procedures for dealing with a flameout in the number 2 engine.
Engine number 2 in fact was working properly, with no signs of a flameout, yet the warning triggered an autofeather maneuver in which the propeller blades turn parallel to the wind so they don’t cause drag, allowing pilots to fly with the remaining engine. The ATCPS helps manage the ATR72’s autofeathering system.
Two months later, tests were conducted under the supervision of U.S, Taiwanese, French and Canadian authorities at the Minnesota supplier’s facility. Those tests showed that the connector, which relays information from the engine’s torque sensor to the autofeather unit, failed tests checking if data could flow continuously and accurately to other flight computers.
Flight data and voice recorder information indicate the pilots continued to shut down the number 1 engine, without realizing their mistake, according to the report.
“We didn’t see some procedures being followed,” Wang said.
The pilot called for an engine restart at least five times during the flight’s final minute, according to a transcript of the voice recorder.
“Wow, pulled back the wrong throttle,” the pilot said nine seconds before impact. It wasn’t clear if he was referring to the original error or the restart procedure.
“Impact, impact, brace for impact” and “pull up” were the final words heard in the cockpit.