Asiana 777 Approached SFO Too Slowly

The Asiana Airlines Boeing 777-200ER that crashed while landing at San Francisco International Airport (SFO) on Saturday had approached the runway at a speed “significantly below” the 137 knots targeted by the crew, according to preliminary data authorities have extracted from the airplane’s flight data and cockpit voice recorders. While briefing reporters Sunday in San Francisco, National Transportation Safety Board chairman Deborah Hersman also noted that during approach, the airplane’s idled Pratt & Whitney PW4090 turbofans appeared to respond normally to throttle command a few seconds before impact.

The airplane’s CVR recorded no discussion of any aircraft anomalies or concerns with the approach, added Hersman. 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. Rescuers sent 182 of the occupants with injuries to area hospitals, some life-threatening, while 123 walked away from the wreckage.

San Francisco airport authorities managed to open three of SFO’s four runways by Sunday afternoon.

Questioned about the operation of the instrument landing system, Hersman cited a Notam (Notice to Airmen) indicating that the airport’s glideslope wouldn’t function from June 1 to August 22, while crews worked on a construction project. However, the ILS’s localizer remained in operation, and airport officials stressed that all required navigation tools at the airport worked properly at the time of the crash. Later, the FAA issued a Notam about inoperative precision approach path indicator lights damaged by the crash.

Although visual flight rules (VFR) prevailed at the time of the accident, Hersman said investigators still didn’t know whether or not the pilots opted to fly the approach entirely “by hand” or with the use of automation such as GPS-based navigation tools in the cockpit.