-LRB- CNN -RRB- -- Boeing is asking pilots who fly its 737 jets to pay careful attention to flight instruments after Dutch investigators said a faulty altimeter contributed to the recent crash of a 737 in the Netherlands . Turkish Airlines Flight 1951 broke into three pieces near Schiphol Airport on February 25 . The 737 is the most widely flown jet in commercial aviation . More than 6,000 have been sold , according to Boeing . `` Boeing reminds all operators to make sure flight crews pay close attention to all primary flight controls during critical stages of a flight , '' Boeing spokesman Jim Proulx told CNN on Thursday . On February 25 , Turkish Airlines Flight 1951 from Istanbul to Amsterdam dropped from the sky on approach to the landing strip at Schiphol Airport , breaking into three pieces in a muddy field . Nine people died and 80 people were hurt in the accident . In a memo to pilots , Boeing says there was a malfunction in one of the plane 's two altimeters , which measure the altitude above the terrain where the plane is going to land . The left altimeter was giving `` erroneous '' information , indicating that the plane was below 7 or 8 feet from ground level when it was actually about 2,000 feet in the air , the memo said . That caused the automatic throttles to slow the plane down . `` Boeing recommends operators inform flight crews of the above investigation details and the -LRB- Dutch Safety Board -RRB- 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 automatic pilot when it crashed , said Pieter van Vollenhoven , head of the Dutch Safety Board . The weather was misty at the time of the crash , possibly keeping the pilots from noticing their altitude , Van Vollenhoven said . Automatic pilot should not be used for landings if altimeters are malfunctioning , he said . Dutch investigators said there had been faulty meter readings on two other flights of the same jet , but the pilots were able to land . In the Amsterdam crash , the pilots did not recognize the altimeter problem until it was too late , Van Vollenhoven said . 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 . '' Proulx said he did not know what that speed was for that particular 737 model . The warning issued by Boeing was for many other models of 737 jets , not just the 737-800 involved in the Amsterdam crash .