What happened
During an en route stop, company maintenance personnel opened the forward overwing emergency exit to access a navigation light requiring repair. While the flight engineer noted that the emergency exit appeared to be in place during the preflight inspection, he did not perform a physical examination of the exits or the latches.
During the climbout phase of the flight, the crew discovered they were unable to pressurize the aircraft. Despite objections from other crew members, the captain decided to proceed with the flight. The crew donned oxygen masks and continued the climb to a cruise altitude of FL330. Shortly after reaching level flight, the captain became incapacitated due to decompression sickness. The first officer assumed command of the aircraft and diverted the flight for an emergency landing at Covington, KY. No injuries were reported.
The investigation
Following the flight, the forward overwing emergency exit door was discovered lying inside the aircraft. An inspection revealed that the exit door would not fit properly within the frame. Furthermore, the door latches failed to engage the latch plates on the frame, even when the handle was moved into the locked position.