What happened
United Airlines Flight 108 received information regarding a bomb threat that included a short time limit. Due to the urgency specified in the threat, the flight diverted to Detroit Metropolitan Airport. The crew initiated an emergency evacuation using the aircraft's slides.
Eight of the ten available slides deployed normally and were used for the evacuation. However, the slide at door 4R failed to inflate and was not utilized. At door 5R, a flight attendant perceived that the slide/raft was inflating slowly. Believing she needed to assist with inflation, she pulled what she thought was the manual inflation handle (MIH). She heard a hissing sound, indicating gas release.
The flight attendant then directed two passenger helpers down the slide. As they exited the aircraft, the slide separated from the fuselage and fell to the ground. One of the two passengers sustained a serious back injury. During the rest of the evacuation, two other passengers suffered serious leg injuries, and sixteen others sustained minor injuries.
The investigation
An investigation into the incident revealed that the flight attendant at door 5R inadvertently pulled the release handle (RH) when attempting to use the manual inflation handle (MIH). Both handles were constructed of canvas material and were approximately the same size. The MIH was red with a piece of white material marked 'PULL' in red letters, while the RH was white and also marked 'PULL' in red letters.
The investigation found no reason for the slide at door 4R failing to inflate. The confusion between the two handles contributed to the premature deployment of the slide at door 5R.