The Asiana Airlines Inc. Boeing Co. 777 that crashed while landing in San Francisco had slowed to almost 40 miles an hour below its target speed before hitting a seawall short of the runway, a U.S. investigator said.
Crash investigators said they don’t yet know why the plane was moving so slowly it was on the verge of losing lift, or whether a pilot with only 43 hours of experience flying that aircraft type was at the controls. All but two of the 307 people on board survived.
Investigators expect to learn more when they interview the four pilots -- two who were flying the plane when it crashed and two who provided relief on the flight from Seoul, National Transportation Safety Board Chairman Debbie Hersman said in a briefing today. She declined to say which pilot was at the controls when the plane crashed.
“They got way slow,” Mark Epperson, a retired Boeing 767 captain and former chief pilot for American Airlines in San Francisco, said in an interview. “That means the auto-throttles either weren’t on, or they selected a speed that shouldn’t have happened.”
One pilot was a veteran on the Boeing 737 who was transitioning to the larger 777, according to the airline. The other was a management pilot overseeing him, Hersman said.
The plane’s impact flung rocks hundreds of feet down the runway and tore off parts of the plane that came to rest in the San Francisco Bay, Hersman said.
While the plane didn’t make any unusual drops or turns as it flew across the bay toward the runway, its speed fell to dangerous levels as it got lower, Hersman said, citing preliminary information from crash-proof recorders.
The pilot flying the plane turned off the autopilot at 1,600 feet altitude 82 seconds before the crash, she said. At 1,400 feet altitude a few seconds later, the plane was flying at 196 mph, she said.
The speed fell as the aircraft neared the runway, dropping below the target landing speed of 158 mph. It got as low as 119 mph three seconds before impact, she said.
U.S. investigators are trying to determine why the pilots didn’t react to the critical loss of airspeed until seven seconds before the crash. Efforts by the pilots to add power and abort the landing came too late to clear the seawall.
The aircraft slowed so much that a cockpit warning of an impending aerodynamic stall sounded four seconds before it crash-landed.
It was the first fatal crash in the U.S. of a large jet since 2001, and Seoul-based Asiana’s first such accident since a Boeing 747 cargo plane went down at sea in July 2011.
Hersman said investigators so far can’t confirm a report in media including the San Francisco Chronicle that one of the two victims, a 16-year-old Chinese girl, may have been run over by a fire-rescue vehicle rushing to the scene rather than killed in the crash. Video isn’t clear enough to determine what happened, she said.
Co-pilot Lee Kang Kuk, 46, has flown a total of 9,793 hours, 43 of which were on a 777, South Korea’s transport ministry said in an e-mailed statement yesterday. Captain Lee Jung Min, 49, a graduate of the Korea Aerospace University who joined Asiana in 1996, has flown a total of 12,387 hours, 3,220 on a Boeing 777, the ministry said.
“It is inappropriate to prejudge that pilots were responsible for the crash, or that there were problems with the aircraft, while the investigation is ongoing,” Choi Jung Ho, an official at the ministry, told reporters today. Control is “easily transferable” between pilots depending on flight situation, Choi said.
A so-called glide slope indicator, which gives pilots a steady descent path, hadn’t been working since June on the Asiana flight’s runway due to construction. The U.S. Federal Aviation Administration had posted a “notice to airmen” warning of the shutdown.
With the glide-scope indicator out, it would be normal procedure for the pilots to turn off the auto-pilot to do a visual approach, Epperson said. If the inexperienced pilot was attempting a manual landing, “then the check airman should’ve been way ahead of that,” he said.
The Asiana flight had been cleared for a visual approach and didn’t need the glide slope to land, Hersman said in a briefing yesterday.
To prevent a plane from going into a stall, which can cause it to lose lift and plummet, cockpits are equipped with a warning system known as a stick shaker. When a plane gets within a few miles an hour of stalling, a device vibrates the control yoke and makes a loud thumping noise.
In investigating the last fatal U.S. airline accident, a 2009 crash involving Pinnacle Airlines Corp.’s Colgan unit in Buffalo, New York, the NTSB found the pilots allowed their plane to get too slow, which also prompted a stick-shaker alert. That alert triggered an abrupt series of maneuvers that caused the plane to go out of control, the safety board found.
It’s common for U.S. airline pilots to land aircraft like the 777-200 with relatively few hours of experience and under the watchful eye of instructors known as check airmen, Epperson said.
“You don’t know where the wheels are until you fly it a few times,” Epperson said. “You’re more cautious, going to flair a little bit higher, round out the landing more.”
The Asiana crew “ran out of ideas, air speed and altitude all at the same time,” he added.