Faulty altimeter a factor in plane crash

A faulty altimeter played a role in the crash at Amsterdam's Schiphol Airport last week that killed nine people, say investigators.

The Turkish Airlines jet was landing on automatic pilot when a problem caused it to slow abruptly far short of the runway, sending it plunging into a muddy field, less than a mile short of the runway at the Amsterdam airport, chief investigator Pieter van Vollenhoven said yesterday.

At 1,950 ft the airplane's left altimeter suddenly and mistakenly registered an altitude of 8 ft below sea level and passed the reading on to the automatic control system, Mr 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, Mr van Vollenhoven said. But the autopilot reduced gas to the engines and the plane lost speed, decelerating until, at a height of 450 ft, it was about to stall. Warning systems alerted the pilots, who responded, but too late to recover.

The Boeing 737-800's flight recorders also showed false readings from the altimeter on two flights before the 25 February crash. Mr van Vollenhoven did not say if pilots had noticed the previous incorrect readings.

The Dutch Safety Authority said it had issued a warning to Boeing during its investigation, asking the company to alert customers that when altimeters did not function properly "the automatic pilot and the gas system coupled to them may not be used for approach and landing," said Mr van Vollenhoven.

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.

Ahmet Izgi, of Turkey's Pilot's Association, told Turkey's NTV news channel that the preliminary Dutch findings were "not satisfactory" and said it would be odd for the pilots not to react to a false altimeter reading in time to save the plane.

Mr van Vollenhoven said the plane carrying 135 passengers was being landed on autopilot, a situation he called not unusual. He said that the pilots had been unable to see the runway at the time the plane began its descent due to the cloudy conditions and light rain. The investigation continues.