Rudder malfunction caused AirAsia crash, says panel

(From Jakarta Globe)

A malfunction in two of the plane’s rudder travel limiter units caused the crash late last year of AirAsia Flight QZ8501, Indonesia’s National Transportation Safety Committee or KNKT, revealed on Tuesday, adding that the pilots had “done everything they could.”

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The committee announced the outcome of its 11-month investigation and concluded that the units had been repaired at least 23 times in the 12 months prior to the crash on Dec. 28, which killed all 162 people on board.

“In the last few months before the incident, malfunction in the plane’s RTLUs occurred more and more frequently,” KNKT chief investigator for the AirAsia crash Nurcahyo Utomo told reporters.

AirAsia’s ground crews had to fix the units twice in October 2014, and the number of malfunction incidents grew to five the following month and finally in December, the units broke down nine times, Nurcahyo said.

The units are responsible for limiting how much the plane can roll, which is set at 33 degrees.

The plane’s rudder had four RTL units, the KNKT said, two of which malfunctioned at least four times during the Dec. 28 flight, as the plane cruised at an altitude of 38,000 feet.

The series of malfunctions caused the Airbus A320-216 to roll at a rate of 6 degrees per second, the investigator said.

The last malfunction caused the plane to roll a total of 104 degrees, plummeting into the Java Sea below at a rate of 20,000 feet per minute.

“The flight crew has done everything they could and followed procedures to respond to the situation. However, the situation was beyond the pilot’s ability to recover,” Nurcahyo said.

An Indonesian pilot and a French first officer were flying the plane.

The tail section of the aircraft was taken to France for further examination by Airbus, the plane’s manufacturer.

The examination revealed that there was a crack in the soldering work of the units’ electrical wiring.

“This caused electricity to flow intermittently to the units,” the KNKT investigator said.

Maintenance crew, the KNKT concluded, failed to take into account the temperature differences the units are exposed to while in the air and on the ground.

“When the airplane is on the ground the units get very hot while in the air, temperatures can drop to minus 5 degrees Celsius. It is these [temperature] differences which may have caused the cracks,” he said.

Besides Indonesia, six countries were involved in the investigation: France, Singapore, Malaysia, South Korea, the United States and Britain.

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