The left-hand flight deck overhead window provides the flight crew with a secondary emergency egress route. The left overhead window consists of three panes of glass, an inner pane attached to the crew compartment and a center and outer pane attached to the upper forward fuselage.

When the secondary emergency egress path is utilized, pulling the T handle located forward of the flight deck center console (between the commander and pilot) activates the overhead window jettison system. When initiated, the center and outer panes are jettisoned as a unit, upward and aft. A time delay in the pyrotechnic firing circuit delays the initiation of the jettisoning of the inner pane 0.3 of a second after the center and outer panes are jettisoned. Upon the initiation of the jettisoning of the inner window pane, it rotates downward and aft into the crew compartment aft flight deck on hinges located at the aft portion of the window frame. A capture device attenuates the opening rate and holds the window in position.

The overhead window jettison system consists primarily of expanding tube assemblies, mild detonating fuses, frangible bolts and associated initiators.

The left overhead window jettison system can be initiated from the outside of the orbiter on the right side of the forward fuselage by ground personnel.

Egress steps are mounted at the aft flight deck station (left side) to assist the flight crew up through the window.

Emergency ground descent devices are stowed on the overhead aft flight deck adjacent to the left overhead window. One device is provided for each flight crew member. The emergency ground descent device enables flight crew members to lower themselves to the ground over the side of the orbiter.