First sign of trouble
As Columbia descended, the autopilot made a series of sharp 58-degree turns to slow the vehicle.
At 0851 the first signs emerged that the shuttle's aerodynamics were not behaving as on previous flights. Columbia started to experience increased drag on its left-hand side. As the drag became more severe, manoeuvring rockets on the right fired in an attempt to compensate.
At 0852 a series of sensors began to show unusual temperature rises in and around the left wing.