Incident Sequence
The aircraft was climbing through 25,000 feet in light turbulence when the crew experienced two jolts accompanied by a loud explosive noise, followed by a sharp roll to the left. A visual inspection revealed that the left overwing emergency escape slide had deployed and separated in flight. The crew subsequently returned to Los Angeles, where the aircraft landed without further incident.
Post-Incident Examination
Examination following the incident disclosed that the slide compartment door was unlatched and open, and the adjacent maintenance access door was also open, with its latching handle in the unlocked position. These findings indicated that the slide was not securely stowed prior to the flight.
Maintenance Background
The flight immediately preceding the incident had triggered two EICAS warning messages related to the left overwing slide door. After landing, maintenance personnel accessed the slide compartment, cleaned a proximity switch, and performed a functional test of the system. The aircraft was then dispatched with no open maintenance items.
The maintenance closing procedure in effect at the time of the incident specified that one mechanic hold the bottom corners of the 33-inch-wide slide door closed while manipulating the latching handle in a maintenance access door located 12 inches aft of the slide door. This procedure was identified as a contributing factor to the door not being properly secured, as the single mechanic could not simultaneously ensure the door was fully closed and correctly latch the handle.
Procedure Revision
Following the incident, the maintenance closing procedure was revised to require two mechanics: one to hold the slide door closed while the second manipulates the latching handle. This change aims to ensure that the door is securely latched before the aircraft is returned to service.