MIA97IA147

The airplane was in cruise flight when a pronounced airframe vibration started. At the same time, the #2 engine thrust reverser armed light illuminated, but no other lights illuminated. The abnormal procedures check was initiated, the #2 throttle was moved to the idle position, and airspeed was reduced. A precautionary landing was accomplished at the departure airport. Examination of the airplane by company maintenance personnel revealed the right wing fixed trailing edge panel had separated and collided with the fore flap and inboard mid flap.

On April 19, 1997, about 1953 eastern daylight time, a Boeing 747-2R7F, N639FE, registered to Wilmington Trust Company Trustee, operated by Atlas Air Inc., as a 14 CFR Part 121 scheduled domestic/international cargo flight, experienced an in-flight failure of the right inboard trailing edge wing skin panel in cruise flight. The pilot-in-command diverted back to his departure airport and landed without further incident. Visual meteorological conditions prevailed, and an IFR flight plan was filed. The airline transport pilot-in-command (PIC), first officer and fight engineer reported no injuries. The flight originated from Miami International Airport, Miami, Florida about 33 minutes before the incident. The destination airport was Bogota, Columbia.

The PIC stated he was level at flight level 290 when a pronounced airframe vibration started. At the same time the No. 2 engine thrust reverser armed light illuminated. No other lights illuminated. The abnormal procedures check was initiated, the No. 2 throttle was moved to the idle position, and airspeed was reduced to 290 knots. As the airspeed decreased the buffet/vibration decreased. The vibration stopped after airspeed reached 270 knots. A landing was accomplished with the No. 2 engine in the idle position. Examination of the airplane after landing revealed the right inboard trailing edge wing skin panel had delaminated and was missing.

According to Atlas Air Manager, Maintenance, South America Area and Miami, N639FE was acquired from Federal Express (FedEx) on April 12, 1997. The airplane was scheduled to have a "c" check on March 4, 1997, at Mobile Aerospace Facility, Mobile, Alabama. Review of a routine card No. 760003 provided by FedEx to Atlas Air on May 1, 1997, revealed that a "THROUGH VISUAL INSPECTION OF UPPER WING FROM AND INCLUDING FUSELAGE FILLET TO W8L 515 FROM CENTERLINE OF L/E TO EXTREME TE INCLUDING #7 #8 SPOILERS RH & I/8 AILERON FOR CLEANLINESS, CONDITION AND DELAMINATION" was conducted on December 29, 1996, in accordance with Boeing Service Bulletin No. 747-57-2261.

Review of N639FE logbooks revealed the No. 2 engine throttle reverser arm light illuminated in-flight after level off on April 18, 1997. The light went off when the throttles were pulled back to idle. Examination revealed a faulty reverser arm switch, and the item was carried as deferred in the logbook. On landing at Miami on the day of the incident, all four thrust reversers operated normally on landing.

Examination of the airplane by Atlas Air maintenance personnel after the incident revealed the right hand wing fixed trailing edge panel had failed. About 1/3 of the panel had departed the airplane colliding with the right hand inboard fore flap and the inboard mid flap. The total time on the airframe is 63,503 hours with 14,697 cycles. The airplane has been operated by Atlas Air for 21 hours and 5 cycles.

Review of Boeing Service Bulletin No. 747-57-2261 indicates that 40 operators sent Boeing 239 service reports on surface cracks, dents, disbonding or water-contamination in the area of the titanium doubler and at the aft end of those panels. In 95 of these service reports, the operators informed Boeing that pieces of the upper panel departed the airplanes in flight. At the time of these service reports, the airplanes had flight hours between 1,110 and 80,920 and flight cycles between 342 and 19,460.