A particular significant enhancement was bailout capability. This is not ejection as with a fighter plane, but an Inflight Crew Escape System[12] (ICES). The vehicle is put in a stable glide on autopilot, the hatch is blown, and the crew slides out a pole to clear the orbiter's left wing. They would then parachute to earth or the sea. While this may at first appear only usable under rare conditions, there are many failure modes where reaching an emergency landing site is not possible yet the vehicle is still intact and under control. Before the Challenger disaster, this almost happened on STS-51-F, when a single SSME failed at about T+345 seconds. The orbiter in that case was also Challenger. A second SSME almost failed due to a spurious temperature reading; fortunately the engine shutdown was inhibited by a quick-thinking flight controller. If the second SSME failed within about 69 seconds of the first, there would have been insufficient energy to cross the Atlantic. Without bailout capability the entire crew would be lost. After the loss of Challenger, those types of failures have been made survivable. To facilitate high altitude bailouts, the crew now wears Advanced Crew Escape Suits during ascent and descent. Before the Challenger disaster, crews for operational missions wore only fabric flight suits.