Washington ( CNN ) -- The Southwest Airlines jet that skidded down a LaGuardia airport runway on its nose on Monday touched down on its front wheels first , which then collapsed , according to federal accident investigators . The unusual landing , in which investigators said the plane 's nose pitched down seconds before touchdown , is the surest clue yet to explain the accident involving the Boeing 737 that injured several people . The National Transportation Safety Board said on Thursday that video and other sources provide evidence that the nose gear contacted the tarmac before the main wheels . Under a normal landing in a big jet , the main landing gear under each wing would touch the runway first and simultaneously -- absorbing the main stress of landing -- and the nose gear then lowered gradually as the plane decelerates down the runway . That model jet is expected to cross the runway threshold at about 140 knots or 161 mph , according to Boeing figures . Investigators said the pilot evidently adjusted the wing flaps less than a minute before landing , suggesting to veteran pilots who spoke with CNN that the plane may not have been on a stabilized approach as it neared the runway . Landing the way it did `` would potentially have overstressed the nose gear to the point where it would have failed , '' said Capt . Mark Weiss , a former 737 pilot and civil aviation leader at The Spectrum Group in Washington . The NTSB said the flaps were set from 30 to 40 degrees about 56 seconds prior to touchdown . `` What this brings into question is whether they were on a stabilized approach to make a normal landing , '' Weiss said . The safety board , coincidentally , is looking at whether Asiana Flight 124 , which crashed-landed in San Francisco earlier this month , was also on a stabilized approach . Details released late Thursday about the New York accident show the plane changing its pitch suddenly in the final seconds of flight -- and in a direction opposite than desired . When the plane was just 32 feet in altitude , four seconds before landing , the plane was pitched 2 degrees nose up . At touchdown , the plane was pitched approximately 3 degrees nose down , the safety board said . Video shows the plane careening down the runway , the nose to the pavement , sending up showers of sparks . After touchdown , the aircraft came to a stop within approximately 19 seconds , the NTSB reported . Southwest said in a statement that the landing scenario the NTSB describes from video and other sources `` is not in accordance with our operating procedures . '' Word that the landing was unusual could remove suspicion of a mechanical failure . Such a conclusion could have major implications for commercial aviation worldwide , given the 737 's status as the most widely used commercial jet . The company operates only 737s and has more than 600 in its fleet .
National Transportation Safety Board Asiana Flight 124 nose gear collapsed on landing in altitude . Plane skidded down runway before coming to a stop ; passengers evacuated down slides . Several people hurt in incident involving largest domestic airline . Boeing investigating ; Southwest .