SAN FRANCISCO — In a critical period of nearly 30 seconds shortly before impact, none of the three pilots in the cockpit of the Asiana jet that crashed here on Saturday mentioned the airspeed of their Boeing 777, the chairwoman of the National Transportation Safety Board said Thursday.
From an altitude of 500 feet — when one of them noted that they had completed a prelanding checklist — to the point where a mechanical system warned them they were within 100 feet of the ground, the cockpit voice recorder captured no mention of speed, said the official, Deborah A. P. Hersman.
Board investigators, who are preparing to wrap up their work at San Francisco International Airport and return to their laboratories in Washington, have not yet found any mechanical problems, Ms. Hersman said. She did not speculate about the cause of the crash, in which two people died and scores were injured. But in the course of releasing facts that painted a dismal picture of crew performance, she also said that in the crash, the plane itself had performed fairly well.
The seats stayed bolted to the floor instead of coming loose and crushing the passengers; the landing gear sheared away cleanly, as designed; and after the crash, the aisle path lighting and the public address system worked. The fuel tanks did not rupture. (A postcrash fire came from oil dripping into the hot section of an engine that had been torn away and ended up resting against the fuselage, investigators said.)
One part that clearly did not work as intended were the emergency slides. Two inflated inside the fuselage, each trapping a flight attendant.
Ms. Hersman also said that the flash of light described at 500 feet by the pilot flying the plane was not noted by the other two men in the cockpit and did not seem to have had much effect.
On Thursday, workers at the airport had cleared the runway, 28L, of aircraft parts and other debris and were preparing to repave and paint new markings, hoping to have it reopened by Sunday or Monday, ending a week of cancellations and delays. Soon they will begin chopping up the hulk of the plane, now visible to incoming and departing flights, and carting it away.
Investigators will have to determine why the autothrottles, which the crew thought were engaged and would maintain safe speed, were not working. Some of the instructions that the crew gave the autopilot may have disabled the autothrottles, experts said.
For example, when air traffic controllers told the crew to make a broad left turn and descend, the flight crew could have moved the autopilot into a mode called "flight level change," a mode in which the autothrottle does not work to maintain speed.
The safety board has not provided much detail, but Ms. Hersman said investigators needed to "validate" the information they had, meaning reconstruct the state of the cockpit automation.
There are two broader issues. One, as Ms. Hersman pointed out, is that the pilots are supposed to closely monitor what the automated system is doing, or what they think it is doing, including maintenance of airspeed. Another is the possibility of overreliance on technology.
Najmedin Meshkati, an engineering professor at the University of Southern California and an expert on human performance, said that pilots' reliance on technology leads to atrophy of critical flying skills, "just like muscle atrophy."
The airport was operating the runway on visual flight rules, because part of the instrument landing system was out of service for construction work on the runway, and the crew, accustomed to automated landings, evidently had trouble with a manual one.
Some degree of automation is essential in planes that fly for 10 or 12 hours, or even more. But, Dr. Meshkati said, "We really need to refrain from irrational exuberance in embracing automation and new technology."
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