Following disclosure that a faulty altimeter played a critical role in the Turkish Airlines B-737-800 (TC-JGE) crash at Amsterdam’s Schiphol Airport on Feb. 25, Boeing is advising 737 pilots to carefully monitor cockpit instruments during critical phases of flight.
The crash killed nine of the 135 people aboard (128 passenger and seven crew) and injuring more than 50 others. Both of the pilots flying the GE/Snecma CFM-56-powered jetliner and a third junior pilot observing, were among the dead. Turkish Airlines Flight 1951 from Istanbul was on final approach to land on Runway 18R when the twinjet slammed into a muddy field and broke into three pieces.
The aircraft maker said the warning results from the preliminary report from the Dutch Safety Board regarding the fatal accident.
Dutch air safety investigators said the readout from the B-737’s flight data recorder shows that one of two altimeters, a device that measures altitude, was faulty, leading the automatic pilot to drastically reduce power, causing a stall on final approach to the Dutch airport.
“Boeing reminds all operators to make sure flight crews pay close attention to all primary flight controls during critical stages of a flight,” says a Boeing spokesman.
Boeing said in a memo to pilots that the left altimeter was giving erroneous information, indicating that the plane was eight feet below ground level when it was actually about 2,000 feet in altitude. That caused the autopilot to cut off engine power, having assumed that the passenger jet had already touched down.
“Boeing recommends that operators inform flight crews of the investigation details and the (Dutch Safety Board) interim report when it is released. In addition, crews should be reminded to carefully monitor primary flight instruments,” the memo said.
The plane was on autopilot just before it crashed in, said Pieter van Vollenhoven, head of the Dutch Safety Board. “The plane was in heavy fog. I think the pilots did not see that a problem was occurring,” he added.
Dutch investigators said there had been faulty meter readings on two other flights of the same B-737-800, but the pilots were able to land. According to conversation recorded between the plane’s captain, first officer and an extra first officer in the jump seat, the pilots noticed the faulty altimeter but didn’t consider it a problem and didn’t react.
An investigations is underway as to why more action had not been taken after the altimeter problem was detected.
In the Amsterdam crash, the pilots did not immediately recognize the problem. “The crew initially did not react to these events,”Van Vollenhoven said. They eventually reignited the engines, but by then it was too late.
The Boeing memo notes that “the autothrottle, which uses the left radio altimeter data, transitioned to landing flare mode and retarded the throttles to the idle stop. The throttles remained at the idle stop for approximately 100 seconds during which time the airspeed decreased to approximately 40 knots below the selected approach speed.”
The warning issued by Boeing was for many other models of 737 jets, not just the 737-800 involved in the Amsterdam crash.