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article imageDutch Boeing 737-800's had 17 altimeter failures in 6 months

By Adriana Stuijt     Mar 11, 2009 in Travel
Dutch KLM airlines' Boeing 737-800s recorded 17 radio-altimeter failures over the past 6 months, similar to the problem identified as the most likely cause of the crash of the Turkish Airlines' Boeing 737-800 two weeks ago, in which 9 people were killed.
This important information - indicating that there may be a structural problem with Boeing's 737-800 passenger lines' altimeters - the instruments which record the plane's height from the ground with radio-waves and are directly linked to its automatic pilot system -- was contained in confidential documents published by the Dutch news-radio BNR. listen
The radio station has been unable to get any comment from Boeing about the issue.
The spokesman for the Netherlands' airline company KLM, however, would neither confirm nor deny the confidential internal report, which BNR radio journalist Guido Vermeulen said they obtained directly from top technical personnel. The technical personnel meanwhile have also launched their own technical investigation of all the company's fleet of Boeing 737-800s' altimeters. KLM would only say that 'they did not have problems at the moment in this regard." They also told BNR that they 'would not comment on whether there had been any such problems in the past.'
KLM-technical investigating all Boeing 737-800s
However, the technicians at the airline have immediately formed their own action group which started examining all its Boeing 737-800s' altimeters - saying that they prefer to work pro-actively and thus are not waiting for any confirmation from either Boeing 's headquarters in the United States, nor from KLM's non-technical management. They said that under the circumstance,s it was 'wisest to have every Boeing 737-800 checked for this altimeter problem at once.'
"Possibly there have even been more failures than we know about, because the suspicion also is strong that there have been 'spike failures' which were never even noticed and thus also were never reported," one unnamed technical engineer at KLM told BNR radio news journalist Guido Vermeulen.
Heathrow airport, KLM plane problem:
The internal, confidential documents which the radio station obtained about the issue, showed that the KLM's Boeing-737 have also had 17 failures of the altimeters over the past six months. The last failure occurred one week after the Turkish Airlines crash, the documents showed.
A KLM Boeing 737-800 was landing at Heathrow airport a week after the Turkish Airline crash when the altimeter failure reportedly occurred. The KLM technical engineers said they then took immediate steps and have started checking all the aircraft. "We can't wait for Boeing to confirm the problem', commented one.
The initial official Dutch government investigation of the deadly Turkish Airlines Boeing-737 crash on 25 February had identified a previously unrecognised altimeter problem as the most strongly suspected cause of the accident in which 9 people had died and 80 people were injured when the plane fell into a farmer's field during its approach to a runway.see
Dutch accident investigation council chief Pieter van Vollenhoven said their initial findings showed that the left altimeter of the crashed airliner from Turkey had failed. The auto-pilot had thus automatically throttled back, reduced its fuel intake and reduced the plane's speed. It was flying too slowly to continue its momentum towards the Polderbaan and crashed in a farmer's field. This damp field had in fact saved the lives of many passengers: 80 were injured mostly with skull- and bone-fractures, but the soft field had cushioned the fall, investigators said.
Left-side altimeter measured minus 8 feet
Van Vollenhoven based these initial findings on the data from the retrieved flight-data recorder, the 'black box', retrieved from the wreckage immediately after the crash. This data showed that the Turkish Airlines Boeing 737-800 was flying too low and too slowly by the time it approached to land on the Polderbaan runway. It was flying on autopilot at 9,150 feet on its approach to the Polderbaan runway -- but the left sided altimeter was measuring their height at minus 8 feet. Only the left altimeter had failed. The right handed side one worked perfectly, he said.
This plane's altimeter had failed twice before
This failure and the accompanying caution alarms 'may not have been considered a problem by the Turkish airline crew' , he noted, as 'they kept flying on autopilot' .
Automatic warning signals - such as severe shaking of the steering column -- were also given off at 150 metres but by that time, it was too late for the crew to respond adequately: the plane by then was flying so slowly that it dropped one kilometre before the landing and crashed into the farmer's field. The black box showed that this left altimeter had failed twice on previous flights of this specific aircraft. This plane has two altimeters.
The Turkish Airlines' left radio-signal altimeter's failed to show the correct height while the plane was being landed on auto-pilot -- and thus the auto-piloted plane took back gas and automatically reduced its air speed. That's why Flight 1951 crashed at 10.31am in the water-logged plowed field. The wreckage now is being cleared away and taken to another location for technical testing.
Warning to Boeing by Dutch crash-investigator chief
This investigation council does not establish any kind of guilt - they only examine what may have happened, Van Vollenhoven said. One warning he did give to Boeing airline company directly however was that they 'may want to change their manual for the Boeing 737-800.' This now states that whenever the altimeters do not work, the autopilot and automatic fuel line facilities may not be used . He said the the company 'may want to reanalyse this instruction to its pilots.'
Van Vollenhoven said this particular aircraft's same left altimeter had also failed twice during eight previous flights: this had been determined from the information gathered from the black box.
"It s measurements show suddenly measured differences in height from 180 feet to a sudden minus 8 feet on the faulty left- altimeter -- and this caused the plane to immediately take back gas, which caused an immediate reduction in speed and height. The plane was by then flying too slowly to continue its momentum and crashed.'
Turkish pilots could not respond in time to altimeter alert:
He said the initial findings determined that Polderbaan runway approach also had a thin layer of low-lying fog which made it difficult to see for pilots flying in manually. The Turkish pilots were using autopilot and did not spot the warning pertaining to the faulty altimeter in time to take it off autopilot and steer the plane themselves. One thing has become crystal-clear however: the manufacturers cannot blame this on 'pilot error', because the plane was so close to the ground by then that the Turkish pilots had no time to respond: crashing within ten seconds. All four Turkish air-crew died in the crash.
This problem with its altimeters now have also been identified by KLM-pilots and -engineers, and which prompted its technical-engineering staff to launch their own independent investigation of its entire fleet of Boeing-737-800s since last Friday, BNR says.
Meanwhile Dutch authorities have started to carefully remove the wreckage of the crashed Turkish Airline Boeing-737, starting with the nose-cone. The wreck had remained in place until the technical- and criminal investigators completed their in-situ examinations. see
More about Klm, Boeing 737-800, Turkish airlines crash, Schiphol airport, Faulty altimeter
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