Incident Overview
On March 22, 2008, at approximately 9:00 am EDT, USAirways flight 1250, a Boeing 757-200 (registration N921UW), experienced the separation of a left upper wing trailing edge panel during cruise at FL270. The flight was en route from Orlando International Airport, Florida, to Philadelphia International Airport, Pennsylvania. The flight crew reported experiencing "light chop" at the time of the occurrence.
The detached panel struck a passenger window at row 19ABC, cracking only the outer portion of the window. The aircraft's pressurization was maintained, and the crew continued to Philadelphia. During the approach, the crew informed air traffic control that they could not increase airspeed due to possible airframe damage. The flight landed without further incident. On board were 174 passengers and 6 crew members; no injuries were reported.
Aircraft and Window Details
The passenger windows on the Boeing 757 feature a two-pane design. The outer pane carries normal cabin pressure loads, while a fail-safe middle pane is designed to withstand pressure if the outer pane is lost. In this incident, the middle pane successfully carried the fail-safe load. Boeing had no records of a depressurization event due to failures of 737, 747, 757, 767, or 777 passenger windows, though outer pane cracking or departure events had occurred previously. The windows are certified for pressure only, with no regulatory or Boeing impact requirements. The outer panes are made of stretched acrylic, which is durable but can crack when struck by a sharp or high-energy object.
The separated fixed trailing edge panel (part number 113N1611-9) and its associated hardware were estimated to weigh approximately 35 pounds, according to a Boeing subject matter expert.
Investigation Findings
The National Transportation Safety Board (NTSB) analyzed data from the flight data recorder and crew statements. The investigation found no substantial change to the aircraft's handling characteristics after the panel separated. Consequently, the event was classified as an incident.
NTSB noted that after problems with the 757 wing panel fastening system were identified in the late 1980s, the Federal Aviation Administration issued an Airworthiness Directive (AD) requiring operators to install a redesigned fastening system. Eastern Airlines, which operated the specific aircraft at the time the AD was issued in 1991, had installed the redesigned system. It was these redesigned fasteners that failed on flight 1250.
Post-Incident Actions
Following the incident, US Airways inspected the wing panels on all of its Boeing 757 aircraft and found fastener issues on several other airplanes. Those issues were subsequently repaired, and the aircraft returned to service. The NTSB issued three recommendations addressing the potential for improperly installed fasteners and spacers.