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On October 16, 1997, between 0830 Pacific daylight time and 1127 mountain daylight time, a Boeing 757-222, N581UA, owned and operated by United Airlines, Inc., sustained minor damage when the left off-wing evacuation slide separated from the airplane during its flight from Seattle, Washington, to Denver, Colorado. There were no injuries to the airline transport-rated captain, airline transport-rated first officer, 6 flight attendants, and 188 passengers. Visual meteorological conditions prevailed, and an IFR flight plan had been filed. The airplane was being operated as Flight 724 in scheduled domestic passenger service under Title 14 CFR Part 121 when the incident occurred. The flight departed Seattle at 0830.
The first officer was flying the airplane. As the airplane was rotated for liftoff, the captain noticed that the EICAS (engine indication and crew alerting system) "EMERGENCY DOOR" light had illuminated. According to United's Boeing 757/767 Flight Manual, if pressurization is normal --- and it was --- the crew need not take further action. During the descent for landing, a flight attendant said she heard a loud noise from the left side of the airplane. The airplane landed uneventfully at Denver at 1127.
DAMAGE TO AIRCRAFT
Postincident inspection disclosed the left off-wing slide had separated from the airplane. The slide was never recovered. There was a 1-1/2 inch tear in the left inboard flap near the trailing edge, a 1-inch tear in the evacuation slide access door, a 9-inch horizontal tear in the honeycomb fillet panel, and a 20-inch tear in the fuselage skin between F.S. (fuselage station) 1420 and 1440. Repair costs were estimated at $75,000.
According to United Airlines, there had been a routine replacement of the left off-wing evacuation slide on the evening before the incident. One of two mechanics involved in replacing the slide was interviewed on November 4, 1997. The mechanic, a 12-year veteran with United, said this was the second time he had replaced the off-wing slide, the first time occurring some 10 years before. The replacement was made during the hours of darkness, using a flashlight and referencing Boeing 757 Maintenance Manuals 25-65-00 and 25-65-01. After installing the slide, he closed the panel and, following the instructions placarded on the maintenance access door, placed the actuator handle in the horizontal position. He said he had never received any training for installing the off-wing slide.
In a meeting with Boeing officials that same day, it was revealed that since the airplane entered service in November 1984, there had been four other incidents similar to that involving N581UA. The first incident also involved United Airlines and occurred on June 8, 1993, in Los Angeles California. The incident was investigated by NTSB's Southwest Regional Office (see LAX 93-I-A245). The second incident occurred on September 23, 1995, at Newark, New Jersey, and involved Continental Airlines. On rotation for liftoff, the EICAS illuminated. The flight continued to Houston, Texas. After landing, it was discovered that the right overwing slide had deployed and was hanging off the right wing. The third incident occurred on November 15, 1995, during a test flight at Everett, Washington. The airplane involved was scheduled to be delivered to Northwest Airlines. The last incident occurred on June 24, 1997, at Dallas-Fort Worth, Texas, and involved American Airlines. The Emergency Doors EICAS light illuminated shortly after takeoff. The airplane returned and landed uneventfully. American Airlines officials said the slide had hung in the slipstream for approximately 10 seconds before separating, causing a discernible airframe vibration.
As a result of these incidents, Boeing issued Service Bulletin (S.B.) 757-25-0182, dated October 10, 1996, and revised it on June 12, 1997. It calls for the replacement of the lockbase retainer and the bearing for the door latch tube, and relocating the door sensor to a forward position on the slide compartment door to enable a more positive indication that the slide compartment door is latched.