Veteran pilots say the recent crash of Asiana Flight 214 might have involved pilots falling victim to what insiders call Flight Level Change Trap (FLCH).
The trap that can catch even long-time pilots by surprise if it’s not closely monitored on an airplane’s final approach raises the question: Is automation meant to improve safety in the cockpit instead sometimes putting safety at risk?
Pilots who have flown using FLCH settings on an airplane’s auto-pilot system say the “trap” can mislead them into thinking the plane’s auto-throttle is giving power to a plane’s engines, when actually, the engines are idle. If the wrong settings are entered into a plane’s computer, the FLCH trap can also make it impossible to increase speed when a pilot needs it.
NBC Bay Area’s Investigative Unit has been examining the growing concern of what one researcher calls “Automation Addiction” in the aviation community: pilots over-relying on auto-pilot, auto-throttle and other forms of automation in the cockpit.
It’s the issue the FAA acknowledged in a Safety Alert for Operators put out earlier this year.
NTSB chairman Deborah Hersman has publicly acknowledged that investigators are exploring the relationship between automation and the pilots in Asiana Flight 214 which crashed landed at San Francisco International Airport back in July. NTSB investigators want to know what role, if any, automation may have played in the inputs and reactions by the three pilots in the cockpit during final approach to runway 28L.
And it’s an issue the NTSB and NASA are both researching in order to find solutions in cockpits to prevent pilots from losing control in flight.
NTSB investigators have also said publicly they are looking into confusion over automation that the black boxes showed occurring in the cockpit of Asiana Flight 214 when it crashed.
Asiana pilots told NTSB investigators they thought the auto-pilot was engaged at the time of the crash. The plane’s black boxes show the airplane dropped below the minimum speed for a safe landing and stayed there for 26 seconds before the pilots started to react, which proved too late to save it from crash landing
NBC Bay Area put veteran commercial airline pilot, Doug Rice, at the controls of a 737 simulator at Flightdeck in Anaheim to show how he thinks auto pilot and automatic computer functions on airplanes can at times be more harmful than helpful.
Rice also demonstrated other instances of how auto pilot and automatic computer functions on airplanes can at times be more harmful than helpful.
“Sometimes the airplane will literally lie to you,” said Rice, a pilot with 35 years of experience.
“It’s automation overload but it’s also become an automation trust,” Rice said. He emphasized pilots can trust the autopilot, as long as they know how to verify it is accurate.
An example of this problem with automation is the FLCH trap. You can see a graphic of how it works to the right.
The green line is the typical glide path most airplanes take in to land. The black line shows planes lowering then moving forward in a stair step motion typical of FLCH.
Pilots set a certain altitude into the computer for the plane to hit. As the plane drops to that altitude, the engines will be automatically put in idle by the computer meaning the engines have no power, to descend.
The trap occurs when pilots don’t realize the plane is in FLCH, not autopilot and they try to engage engines, but since they are in idle, they get no power and cannot increase speed, which can lead to a crash.
Rice demonstrated this in the 737 simulator.
He showed that if pilots try to increase the speed while in FLCH, they can’t because the engines remain in idle. Rice even pulled up on the autothrottle to get power to the engines but unless the pilots over-ride the computers, the auto-throttle will give the plane no power.
“As the pilot pulls back on the yoke, expecting the throttles to come up, they don’t. Speed decreases and he runs out of air speed,” Rice explains.
No power, idle engines, a pilot cannot increase the speed in FLCH. Trying to do this too close to land can end in a crash.
“That is the bottom of the trap,” Rice said.
Data shows the Asiana 214 flight started its final approach to land high of the typical final approach glide path. The NTSB also said the plane was unstable on final approach. Data publicly released shows Asiana’s engines remained in idle most of the way down the glide path and that as the plane lost airspeed it dropped below the line of a typical final approach.
NTSB investigators are still piecing together all this data to arrive at a official determination about what happened. That official determination about what factors played a role in the crash is expected to be released within the next 12 to 18 months.
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