Jet on verge of stalling before crash
The Asiana Airlines jetliner that crash-landed at San Francisco International Airport was flying far below its intended landing speed and on the verge of stalling before the aircraft clipped the sea wall and slammed into the runway, federal accident investigators said Sunday.
The targeted landing speed for the Boeing 777-200ER is 137 knots, and the South Korean jetliner was “significantly” below that, said Deborah A.P. Hersman, chairwoman of the National Transportation Safety Board. Independent flight tracking data indicate that the wide-body’s airspeed might have dipped to as low as 85 knots in the moments leading up to the crash.
Hersman said there was a call in the cockpit to increase speed seven seconds before the plane’s tail struck the sea wall that separates the airport’s runway from the bay. According to onboard flight and voice recorders, the pilots received a warning four seconds before impact that the aircraft was approaching a stall -- a speed so low it can no longer generate enough lift to stay aloft.
At 1.5 seconds before impact, there was a call for the plane to abort the landing and circle around, Hersman said. By then it was too late, as the jetliner crashed and broke apart, killing two passengers and injuring dozens of others. The plane was carrying 307 people.
Asked whether pilot error may have been a factor, Hersman said: “Everything is on table right now. Nothing has been ruled out.”
A spokeswoman for Asiana Airlines in South Korea told The Times late Sunday that the pilot of the plane, Lee Kang-kook, had only 43 hours of experience flying Boeing 777s. Lee has been flying since 1994 and is a “very experienced pilot” with other types of planes, including Boeing 747s, 737s and A320s, said spokeswoman Lee Hyo-min.
But “he was in training for B777,” she said, adding that he had 9,793 hours of flight time. She said Lee had traveled to San Francisco International previously, “but with B777, not much.” She would not specify whether Saturday’s flight was the pilot’s first to SFO in a 777.
She identified the co-pilot as Lee Jung-min, who has logged more than 12,000 flight hours. “He had lots of experience with the B777,” the spokeswoman said.
Hersman said the comprehensive investigation of Saturday morning’s crash would evaluate the airport’s geography, the jet’s cockpit instruments, seats and windshields, flight plans, and the training and experience of the crew, whom investigators hope to interview “in the next few days.” She estimated that the review could take more than a year.
If the accident occurred because of pilot error, it will probably focus new attention on what aviation industry experts have called “automation dependency,” a growing trend among pilots to rely so heavily on computerized flight systems that they lose their own proficiency to fly an aircraft without assistance. A key automated landing system at San Francisco was taken out of service last month; the device helps pilots follow the proper glide slope to the runway.
Jim Hall, a former NTSB chairman, said the growing reliance on automated cockpit controls will probably get a close examination in the aftermath of the Asiana crash.
“There is an overuse of the automatic pilot, without the pilots maintaining their skills to fly the airplane,” Hall said.
“Automation is your friend, but in rare cases it can be your enemy.”
On the positive side, Hall said that improvements in seat design and flame-resistant materials used in commercial airliners probably increased the survivability of Saturday’s crash. He noted that in the late 1980s, the Federal Aviation Administration required passenger seats to withstand forces 16 times greater than gravity, a near doubling of the previous requirement.
Aviation safety experts agree with Hersman that the Asiana flight was not going fast enough to make a safe landing.
“They were coming in too slow,” said Barry Schiff, a former TWA captain with 34 years’ experience and now an expert witness in aviation litigation. “They just weren’t accustomed to making visual landings without coupling their systems to the instrument landing system.”
This is of particular concern for international pilots who’ve grown accustomed to navigation aides during long-distance flights and who don’t land as often as pilots on shorter domestic routes.
Schiff said it appeared as though the pilots “got behind the airplane, meaning that they didn’t correct for deviations as quickly as they were supposed to.”
Flight logs, published by the website Flightaware.com, show that the Asiana flight appeared to be approaching San Francisco International a bit fast at just below 2,000 feet elevation, going about 38 knots faster than an Asiana Boeing 777 the previous day.
By 1,400 feet altitude, the plane had slowed but was still going 17 knots faster. But by 600 feet altitude, the Asiana flight had slowed significantly to 130 knots, now 32 knots slower than the flight the day before.
The logs show that the speed kept declining all the way to 109 knots at 100 feet, far slower than normal for a landing. The pilot appeared to try to pull up to 200 feet of altitude, but that brought the airspeed all the way down to 85 knots, around stall speed.
Even at the lightest possible weight and maximum amount of flaps, both of which would allow lower speed, the Asiana flight was going too slowly. The stall speed at minimum weight and maximum flaps was about 87 knots, according to available data. It is not known whether the aircraft actually stalled.
Schiff contended that the Asiana pilots might not have been properly trained or had lost proficiency because of automation dependency.
International pilots make one landing every 10 hours, Schiff said, and those arrivals are often shared with other crew members. Many of the landings are made with the help of autopilots, he added.
The Boeing 777, for example, is capable of a fully automated landing, and in many cases airlines and their crews allow computers to do the entire job.
“Technology changes our skill levels,” Schiff said.
At San Francisco International, the instrument landing system has several devices to assist pilots. A “glide slope” controls descent angle, and another instrument called a “localizer” controls lateral movement. Both send radio signals to aircraft to make adjustments.
On the airfield is a lighting system called the “precision approach path indicator,” a visual reference that warns pilots when they are not at the correct descent angle.
Hersman said the glide slope device at SFO has been shut down since June because of airfield renovations and that pilots were sent a notice. She said the localizer and lighting system were working, though the lights were significantly damaged by the crash.
The NTSB will be “taking a look at it all,” she said.
Hersman stressed that it is not yet known whether the pilots were using those tools or relying on other onboard GPS-based technology.
In recent decades, the safety of South Korean airlines has become an issue. The NTSB blamed pilot error for a 1997 Korean Airlines crash in Guam that killed 228 people, in which the crew descended too fast and flew into a hill. Two years later, two Korean cargo jets crashed. Since 1980, more than a dozen Korean aircraft have been destroyed in crashes.
Yoon Young-Doo, Asiana Airlines’ chief executive, said at a new conference Saturday that the company’s Boeing 777-200ER was only 7 years old and had no known engine or mechanical problems.
Times staff writers Matt Stevens and Lee Romney contributed to this report.