The flaw in the Silverliner V cars was found by chance, Knueppel said. Shortly after midnight on Friday, an inspector noticed a train car tilting to one side slightly more than another car it was linked to. Inspection of the car at SEPTA's Powelton Yard revealed a 10-inch-long crack in a 350-pound equalizer beam, a piece that transfers the weight of the car to the axles. The crack, which appeared where a plate was welded to the beam, had totally severed the equalizer beam. Pressure between cars was holding the beam together tightly, Knueppel said, but if the beam had given out while a train was in motion a serious accident - even a derailment - could have resulted.