The Asiana Airlines Boeing 777 aircraft that crashed Saturday was a miracle of modern flight technology, automation and safety features — but that wasn’t enough to forestall disaster.
Now, experts say the crash at San Francisco International Airport, which killed two 16-year-old students and left dozens hospitalized, is renewing questions about the complexity of modern aircraft and whether it is outpacing the ability of pilots to know what is going on at all times.
According to disclosures by the National Transportation Safety Board at a news conference Tuesday in San Francisco, the Asiana captain and the instructor supervising him on Flight 214 believed a system was engaged to control the aircraft’s power and speed as it descended and realized too late that the system — called an auto-throttle — was not maintaining speed.
The head of the NTSB offered no explanation for how that might have happened and urged caution about reaching a conclusion about the cause of the crash but made clear that pilots are responsible for monitoring their aircraft.
Modern aircraft like the 777 are so capable of flying themselves that pilots come to over-rely on their automated systems, said Bill Waldock, professor of air safety science at Embry-Riddle Aeronautical University in Prescott, Ariz.
“You’re trusting it, and you feel comfortable in circumstances you shouldn’t,” he said.
Experts call this “automation complacency,” and they say it’s just one of theproblems that can arise when a flight crew finds itself in unexpected situations.
“The airplanes have become so complex,” said J.F. Joseph of Joseph Aviation Consulting in Texas.
Aircraft designers “have decided that pilots are better system monitors than they are being in the middle of things,” Joseph added. “With all the automation, GPS and everything else, taking off and flying from Point A to Point B, the most difficult thing is having enough newspapers to read en route. Not that they’re reading newspapers, but you do become quite bored with it.”
NTSB Chairman Deborah Hersman said that the pilot and instructor seated next to him stated they had programmed the auto-throttles, which operate like cruise control in cars, to maintain the target landing speed of 137 knots. At 200 feet altitude, the pilots realized the auto-throttles weren’t maintaining speed.
Investigators found the devices set in an “armed” position, meaning the throttles were ready to be engaged. But it’s unclear if the pilots set them properly so that they would maintain the proper air speed.
“We need to work to understand what the different modes are and what the crew understood,” Hersman said. She said investigators are working with Boeing, “which is providing us with information about systems and how they are designed.”
She cautioned against jumping to conclusions. But, she added: “Let me be clear: The crew is required to maintain a safe aircraft, and that means they need to monitor. We have the flying pilot and two other pilots, and they need to monitor functions. One of the very critical things that needs to be monitored on landing is speed.”
Douglas Moss of AeroPacific Consulting in California and Reno, Nev., said that a detail disclosed by the NTSB chairman suggests “the two pilots may not have been coordinating their efforts well together.”
An instrument called the “flight director” was switched on for the flight instructor seated in the right seat but off for the captain piloting the aircraft from the left seat. The instruments — which tell where to put the nose of the airplane in terms of pitch and bank — are traditionally either both on or both off, Moss said.
“It’s very possible the captain in the left seat believed the plane was flying in a certain mode and the captain in the right seat thought it was in a different mode,” Moss said.
There’s a name for that, too. It’s called “mode confusion.”
“A lot of times pilots get confused and don’t understand what the airplane is doing,” he said. “It’s a common issue.”
Hersman said the flight instructor told investigators that as the aircraft descended to 4,000 feet, it was slightly high. They set a vertical descent of about 1,500 feet per minute and also were correcting for a deviation from the center line of the runway.
At about 500 feet, he realized they were too low and told the pilot to pull back. At 200 feet, lightson the runway called PAPI, for Precision Approach Position Indicator, were all red, indicating they still were too low. He also realized that the auto-throttles were not maintaining speed.
“He went to push the throttles forward, but the other pilot had already pushed the throttles forward,” Hersman said.
Seconds later, as the plane struggled to gain altitude, its tail struck the seawall at the end of the runway and broke off, and the plane spun 360 degrees before coming to rest.