Uncontained engine failure.

It happens very rarely. But when it does, as on Tuesday aboard Southwest Airlines Flight 1380, it can be one of the most harrowing and dangerous events involving a commercial airplane.

Flight 1380 departed New York’s LaGuardia Airport Tuesday morning bound for Dallas’ Love Field and was cruising at a little over 31,000 feet when passengers reported hearing a loud boom and felt the Boeing 737-700 shudder. Instantly there was a drop in air pressure caused by the rupture of one of the windows over the left wing. A female passenger sitting next to that window was sucked part way out the broken window before being dragged back into the aircraft by fellow passengers.

Passengers reported in media interviews and in online comments that several other passengers with medical training worked feverishly to keep the woman alive while the crew took the damaged plane into a steep dive toward the Philadelphia airport. They shed 21,000 feet of altitude in five minutes and brought the plane to a safe landing. But officials with the National Transportation Safety Board later said one passenger – presumably the woman partially sucked out of the plane – had died in the incident. The dead passenger’s name was being withheld pending notification of next of kin.

That death was the first resulting from an accident involving a U.S. certificated-airline in a little over nine years, ending the longest run of fatality-free flying in U.S. airline history. The last death resulting from an accident involving a U.S. airline came in February 2009 when all 49 people aboard Colgan Air Flight 3407 died in a crash near Buffalo, New York, plus one person on the ground.

Crash investigators from the NTSB, assisted by representatives of Southwest, Boeing and engine-maker CFM International (a partnership between GE and France’s Safran) now will begin the process of determining what caused the deadly accident, which could take weeks, if not months. But pictures of the crippled plane are enough to arrive at the obvious general cause: uncontained engine failure. The guts of the front third of the plane’s No. 1 engine, mounted under and slightly ahead of the left wing, are clearly visible. The front third of the engine’s housing, called the cowling, is mostly gone, with only shards of aluminum left.