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Cause for Turkish Airlines flight known: Dutch Safety Board issues warning
Last Wednesday, a Turkish Airlines flight crashed in a field just 1 kilometer short of the runway at Schiphol Airport in Amsterdam. The report as to what caused the accident has been released. After reading through it myself, and thanks to the paired down version of Gadling's own Kent Wien, pilot and writer of Cockpit Chronicles, here are the details.
According to the report, there was a malfunction of one of the radio altimeters, the device that displays the distance of the airplane from the ground. The left altimeter, instead of reading the Boeing 737's actual height at 1950 feet when the plane was descending, it read 8 feet.
At the point of the glitch, the auto-throttles went to idle because the reading said the plane was just above the runway thus about to land. This caused the plane to slow down more than it should have. The pilots didn't have enough time to recover the speed needed to pull the plane out of a stall to a higher altitude in order to achieve a safe landing.
Along with determining the malfunction in the radio altimeter, the investigation also found out what happened to the plane upon impact. The tail of the plane hit first, then the undercarriage. When the plane hit the ground it was going at 150 kph. A normal landing speed is 260. Because the ground was soft, the plane had a "rapid halt" within 150 meters.
During landing, the tail broke off and the plane ruptured at the business class section which is where most of the fatalities and injuries occurred. Eighty passengers in all were injured and nine people died (4 crew, including the pilots and five passengers). The area of the plane around the wings was the most intact.
There are still investigations being made surrounding the altimeter's malfunction and the Dutch Safety Board has issued a warning to Boeing.
For the report, click here. Prior to these findings, one theory about the cause of the crash was wake turbulence caused by a larger plane landing right before this plane's attempt. (See article.)
Reader Comments (Page 1 of 1)
Dave Mar 5th 2009 2:33PM
It was a 737 not a 747
Jamie Rhein Mar 5th 2009 2:58PM
Dave, thanks for the catch. Change made.
jmchez Mar 5th 2009 2:44PM
So, in effect, the pilots were letting the plane land itself. By the time they became pilots once again, the schizoid computer had already sealed their fate.
Kent Wien Mar 5th 2009 8:11PM
That's about it.
But part of letting the autopilot do it's job is monitoring carefully. I find it more trouble than it's worth to fly a 'coupled' approach using the autopilot. Much easier and more fun to hand-fly.
That said, the malfunctioning radio altimeter shouldn't have caused an airplane to crash. It was a completely bizarre scenario, for sure.
Arnoud Mar 6th 2009 4:13PM
As I live 2.5km from the crash site, I probably have a more than average interest in what caused the plane to crash. Obviously the pilots should have switched off the autopilot when they discovered the malfuntioning altimeter as the procedure apparently dictates, however, what surprises me is the almost complete lack of criticism in the media on the outdated control system. How come there are thousands of large passenger carriers flying around in 2009, that have an autopilot system where a single altimeter is directly coupled with the gashandles during the critical stage of a landing approach. No sensor redundancy, no filtering, no alarms. If the left altimeter happens to drop its reading from 2000 to 0 ft instantly, the control system believes it and acts on it immediately by shutting down the engines. Unbelievably primitive and dangerous. I work in the Offshore Oil and Gas industry where e.g dynamic station keeping of vessels is very common. Although the safety risks here are much lower than in airplanes carrying hundreds of passengers, these Dynamic Positioning systems require three independant position references that should all three be operational in order to activate the system. When one of the references malfunctions or shows erratic behavior, the DP computer will reject the data and set of alarms to warn the operator, while maintaining position using the other sensors. I know the 737 design dates back to the 60's, and I also realize that technology advancements in aircraft are slow for QC and safety reasons, but I'm flabbergasted that neither Boeing nor authorities have corrected for this design flaw. What else is in the air and will hit us in the time to come, caused by similar archaic designs? Isn't it time for a review of these systems in older type airplanes?
Syed Mohammad Husain Aug 1st 2012 4:48PM
They were flying in Instrument Meteorological Conditions (on instruments) according to the report. The Radio Altimeter malfunctioned at a radio altitude of 1950 feet (AGL). The elevation at the airport is if I remember correctly is minus 15 feet (below sea level).
In ILS Category 1 and 2 landings one is supposed to overshoot safely if the runway or the approach lights are not in sight or the system or instrument malfunctions at a much lower altitude, i.e., 300 feet to 150 feet HAT (height above touchdown).
There was a safety altitude present here when the malfunction occurred.