Date: 201307
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: B757 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Mission: Test Flight / Demonstration
Flight phase: Cruise
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ; Tower ZZZ
Aircraft component: Escape Slide
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Situational Awareness
Second reporter function: Pilot Not Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Declared Emergency
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Human Factors

Narrative: During Flap Load Relief Check; the Left Overwing slide [raft] deployed at approximately 160 KTS and separated clear of aircraft. This occurred over open water. Accomplished procedures IAW QRH. Declared an emergency; flew over unpopulated areas. Landed. Requested runway be checked for debris (slide cover found). Wrote up wing slide in Logbook. De-briefed crew and Maintenance.

Callback: Reporter stated the B757 aircraft had been sitting in storage for two years; then flew for a while and had just completed a Heavy Maintenance Check when they arrived to perform the first Flight Test. He was the Captain flying with two other pilots. The Overwing Slide Warning light had come on earlier; shortly after level off; and then came on again about an hour later during the Flap Load Relief Check. The B757 then rolled 'hard to the left' and required full right aileron to compensate. He thought he had lost a section of flap. One of the onboard Maintenance technician's told him he saw the slide deploy; but did not seem to inflate; then tore away from the aircraft. Reporter stated he was shocked by how much of a roll the aircraft took when the slide deployed. He suspects the Flaps-20 approach configuration they were in; during the Test Flight; may produce a greater low pressure area at the upper wing. The uncommanded slide deployment marked up the wing to body fairing and damaged the upper surface of the Inboard (I/B) flap. He recommends that pilots do not delay setting up their flap configurations while on approach due to the strong roll effect on the aircraft if one of the Overwing slides should deploy. He has many hours of flight time and even with that experience; he was not sure he would have been able to recover from that much roll; close to the ground if he was on approach.Reporter stated the Airworthiness Directive (A.D.) for the Overwing Slide Warning light and Slide door had not been accomplished on that aircraft. However; the time period for accomplishment was still within the window that the FAA had allowed in their A.D. He was later told the FAA was now seriously reconsidering the length of time allowed for Operators to comply.

Second narrative: Flight was first flight of Heavy Maintenance Check for a B757 aircraft. Performed Flight Checks on climbout. After initial level off; noted Left (L) Slide on EICAS with EMER DOOR on Overhead discrete. Scanned wing area and fuselage in the area of [Overwing] slide and it appeared secure. Based on experience; elected to continue the Test Flight. Approximately one hour into the flight; in the Approach Configuration; the [Overwing] slide deployed and then departed. The aircraft was offshore; approximately 120 NM. The crew declared an emergency and returned to [the departure airport.] Completed procedures in accordance with QRH and landed. Request FOD check on roll out. Airfield Management recovered the slide pack on the runway.

Second callback: Reporter stated they departed in the B757 after the aircraft had been released from Heavy Maintenance to perform a Functional Check Flight; and then do a Flight Test lasting approximately two hours. He was observing and comparing two different Flight Test Cards for B757 aircraft during their Flight Test. They were about 16;000 FT; cruising to the Test Area when the Left Slide light came on. The aircraft experienced a 'pretty good roll' that was corrected by the pilot flying. One of their Maintenance technicians onboard said the Overwing slide had deployed; stayed attached for about ten seconds; creating a lot of noise inside and outside the cabin and then separated from the aircraft. After they returned to the departure airport; the onboard mechanics said the Overwing Door latches were the issue.

Synopsis: Three pilots report the Left Overwing (Off-Wing) Slide raft deployed during a Functional Test of a B757 after the aircraft was released from a Heavy Maintenance Check. Pilot flying noted he was shocked by how much left roll the aircraft experienced; requiring full right aileron to correct and questioned whether recovery would be possible on approach.