 The recovered Able second stage showed no sign that engine ignition or operation had taken place, and the most probable cause of the failure was believed to be aerodynamic flexing of the Able adapter which then ruptured the Atlas's LOX tank.The crippled booster continued to fly for a few seconds afterwards, but the structural collapse of the Atlas's forward section combined with the loss of LOX pressure to the propellant feed system resulted in engine shutdown and vehicle self-destruction.As a result of this failure and Mercury-Atlas 1 five months earlier due to a similar episode of aerodynamic bending in the forward portion of the LOX tank, GD/A began requiring that all Atlas upper stage/payload combinations undergo proper structural dynamics testing.