AMSTERDAM (AP) -A false reading from a faulty altimeter caused
an autopilot to sharply slow a Turkish Airlines jet short of the
runway last month, sending it plunging into a muddy field and
killing nine people, Dutch investigators said Wednesday.
The flight carrying 135 passengers and crew crashed a kilometer
(less than a mile) from Amsterdam's Schiphol Airport as it was
landing on Feb. 25. The pilots were among the dead.
One of the plane's altimeters, a device that measures altitude,
had registered that the plane was flying below sea level and caused
the autopilot to rapidly reduce power before the crash, officials
The Boeing 737-800's flight recorders showed false readings from
the same altimeter on two flights before the crash, chief
investigator Pieter van Vollenhoven said. He did not say if pilots
had noticed the previous incorrect readings.
The Dutch Safety Authority said it had issued a warning to
Boeing as a result of its investigation, asking the company to
alert customers that when altimeters are not functioning properly
"the automatic pilot and the gas system coupled to them may not be
used for approach and landing," Van Vollenhoven said.
Boeing said it was reminding all operators of its 737s to
carefully monitor primary flight instruments during critical
phases, adding that it was carefully monitoring the fleet.
The deputy chairman of the Turkey's Pilot's Association, Ahmet
Izgi, told Turkey's NTV news channel that the preliminary Dutch
findings were "not satisfactory" and said it would be odd for the
pilots to not react to a false altimeter reading in time to save
Van Vollenhoven said landing the plane on autopilot was not
unusual and the pilots could not see the runway as the plane began
its descent because of clouds and a light rain.
At 1950 feet (around 700 meters) the airplane's left altimeter
suddenly and mistakenly registered an altitude of 8 feet (about 2
meters) below sea level and passed the reading on to the automatic
control system, Van Vollenhoven said.
According to conversation recorded between the plane's captain,
first officer and an extra first officer on the flight, the pilots
noticed the faulty altimeter but didn't consider it a problem and
didn't react, Van Vollenhoven said.
But the autopilot reduced gas to the engines and the plane lost
speed, decelerating until, at a height of 450 feet (150 meters) it
was about to stall. Warning systems alerted the pilots.
"It appears that then the pilots immediately gave gas, full
gas, however it was too late to recover," Van Vollenhoven told
reporters. He said it would be for courts to apportion blame.
The plane fell into a freshly plowed field, striking the ground
tail first and breaking into three pieces.
Eyewitnesses said it seemed to fall from the sky. Passengers who
survived had noticed the pilot gunning the engines at the last
minute. Some didn't realize the landing had gone wrong until other
passengers began opening emergency doors.
Those killed in the crash included five Turks and four
Turkish Airlines said the dead included the three pilots. It
described the captain, Hasan Tahsin Arisan, as an experienced pilot
and air force veteran.
The company has said it will pay compensation to victims and
The American dead included three Boeing employees on a business
trip unrelated to the flight.
As of Wednesday, 28 survivors are still hospitalized.
The investigation is expected to last until the end of the year.
Van Vollenhoven said that from now on "the technical investigation
will be directed at the functioning of the automatic pilot, the
automatic gas control system, and their coupling to the radio
The Turkish pilot's association had earlier suggested the crash
was due to "wake turbulence" from a large plane, a Boeing 757,
that had landed at Schiphol Airport two minutes earlier.
Wake turbulence forms behind an aircraft as it passes through
Boeing's 737 is the world's best-selling commercial jet, with
more than 6,000 orders since the model was launched in 1965.
The 737-800, a recent version of the plane, has a "very good
safety record," said Bill Voss, president of the independent
Flight Safety Foundation in Alexandria, Va.
Associated Press Writer Gulden Alp contributed to this report