Asiana Critical of Boeing 777’s Autothrottle Design
While Asiana Airlines acknowledges the culpability of its pilots in the loss of airspeed that ultimately caused the July 6 crash of one of the carrier’s Boeing 777-200ERs on approach to San Francisco International Airport, it also blames the design of the airplane itself, calling the warning system to alert the flight crew that the autothrottle had stopped maintaining airspeed “inadequate.” According to documents released by the U.S. National Transportation Board on Monday, Asiana also claims that inconsistencies in the aircraft’s automation and autothrottle logic that disabled the aircraft’s minimum airspeed protection contributed to the failure of the crew to monitor and maintain a minimum safe airspeed during final approach, resulting in the deviation from the intended glide path. Apart from inadequacies in the autothrottle system, the airline notes that a low-speed alerting system did not provide adequate time for recovery in an approach-to-landing configuration.
In its report, Asiana recommends that the FAA require Boeing to make several changes to the 777’s cockpit design, including a modification to the low-speed alert system to provide an aural alert, thereby allowing a margin for conducting a safe go-around based on normal pilot reaction time with the engines at idle and the airplane at a low altitude.
For its part, Boeing cited “numerous cues,” both visual and tactile, that alerted the crew to decaying airspeed, an incorrect thrust setting and the fact that they allowed the aircraft to descend increasingly below the glide path. “These cues pointed to an increasingly unstable approach, which should also have caused the crew to initiate a go-around,” it added.
Other conclusions cited by Boeing include the finding that the pilots’ own actions and deviation from procedure led to a condition in which the autothrottle did not resume airspeed control.
The subject of the airplane’s autothrottle system gained prominence early in the crash investigation, when the pilots advised the NTSB that they had armed the device to maintain a 137-knot landing speed. However, three seconds before it hit the sea wall at the threshold of Runway 28L, the airplane had slowed to just 103 knots.
The airplane’s CVR recorded no discussion of any aircraft anomalies or concerns with the approach. One of the crewmembers did call for more engine power some seven seconds before impact, however. About three seconds later, the stick shaker activated, indicating an imminent stall, and only 1.5 seconds before impact the crew called for a go-around.
Two of the 307 passengers and crew aboard Asiana Flight 214 died after the tail of the 777 struck the sea wall at the threshold of SFO’s Runway 28L upon landing, sending it careening off the pavement and into a partial spin until it came to rest several hundred feet from the point of impact. A third passenger died when a rescue vehicle ran over her while she lay injured beside the wreckage. It was the first fatal accident involving a Boeing 777.