Here's why you shouldn't lean on train doors. Two doors on a JFK Airport AirTrain fell off the shuttle — which had just undergone maintenance work — as it picked up its first load of passengers yesterday, according to the Post.

As the two-car train pulled into the Lefferts Boulevard stop at 3:30 am, one door fell off its hinges onto the tracks, while the other became "embedded into the concrete platform like a knife into a birthday cake." When the incident occurred, no one was aboard the AirTrain, which has no conductor or motorman, and the shuttle completed its route without passengers and was taken out of service. Insiders told the paper the doors may not have been attached properly and that "all indications are that there was a problem in the maintenance yard." An airport source said the incident was "very troubling," but could have been worse. "[Had] it happened when the train was crowded, people would have fallen out — and they'd now be dead."