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NTSB Calls For Special Review Of Boeing 777 Speed Control

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The NTSB is recommending that theFAA convene a special certification design review to investigate how Boeingcontrols airspeed in theBoeing 777’s automatic flight control system.

The call for a special review, an option the FAA rarely uses, is one of 27 recommendations the Board voted to accept today as part of the final hearing on July 6, 2013, crash of Asiana Airlines Flight 214 in San Francisco.

Three passengers were killed and 187 injured when the 777-200ER struck the sea wall ahead of the runway 28L after a visual, hand-flown approach that resulted in the aircraft flying too slowly with its engines idled. The NTSB issued 15 recommendations to the FAA, four to Asiana Airlines, two to Boeing and six airport rescue and firefighting groups and the airport operators.

In its probable cause finding, the Board laid the blame for the accident squarely on the pilots, who “mismanaged the airplane’s descent,” inadequately monitored aircraft performance and delayed a go-around decision until too late despite being aware that the aircraft was “below acceptable glide path and airspeed tolerances” earlier in the approach.

Also included in the probable cause however was the pilot-flying’s “unintended deactivation” of the 777’s automatic airspeed control, an action that investigators linked in part to his confusion about the operations of the Flight Level Change (FLCH) mode of the automatic flight control system. Mode confusion topped the list of five contributing factors, with investigators finding that “complexities of the autothrottle and autopilot flight director systems that were inadequately described in Boeing’s documentation and Asiana’s pilot training” increased the likelihood of mode error.

While the 777’s autothrottle system will typically respond to dangerously low speed conditions by automatically increasing power, the FLCH mode includes a “hold” mode, noted in text on the flight displays, where the automatic activation does not occur, by design. The pilot-flying selected the hold mode late in the approach, and did not call out the change to the pilot-monitoring. The aircraft’s speed dropped well below target levels as he attempted to maintain glideslope without adequate power, with a go-around initiated too late.

Other contributing factors include the pilots’ “non-standard” communications and coordination regarding the autothrottles and autopilot, the pilot-flying’s “inadequate training” for visual approaches, the pilot-monitoring’s inadequate supervision and flight crew fatigue after the overnight flight from Seoul. The pilot-flying in the left seat was completing his transition to become a 777 captain after flying the A320 as a captain for five years, while the pilot-monitoring in the right seat was conducting his first flight as a newly certified 777 instructor.

The NTSB has called for special certification reviews (SCRs) “six or seven times” in the past as part of accident reports on aircraft including the Robinson R44 helicopter, ATR 72and Mitsubishi MU-2 twin turboprops, said John DeLisi, director of the NTSB’s office of aviation safety. “And in six of the seven times the Board has previously recommended an SCR, we have closed that recommendation with an acceptable action,” he said.

The SCR recommendation was a point of contention among board members, two of whom voted for keeping the language in the final report and two of whom wanted it removed. A tie vote means the language remains, although members can file dissenting opinions as part of the final report.

Boeing disagrees with the NTSB’s assertion that the 777’s auto-flight system contributed to the accident, “a finding that we do not believe is supported by the evidence”, the company said in a statement. “We note that the 777 has an extraordinary record of safety”, the company added, with auto-flight system used successfully for over 200 million flight hours across several airplane models, and for more than 55 million safe landings. “

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