History of Flight
On May 19, 2013, at about 1245 eastern daylight time, China Airlines flight 5254, a Boeing 747-400F freighter with registration B18701, suffered a partial separation of the right inboard foreflap while on approach to runway 27L at Hartsfield-Jackson Atlanta International Airport (ATL). The flight crew executed a go-around and subsequently landed safely on runway 28 at approximately 1258. Portions of the separated foreflap were found on buildings and the ground roughly 4 to 5 miles east of the airport. The three crew members and persons on the ground were uninjured. The aircraft was operating as a scheduled international cargo flight under 14 Code of Federal Regulations Part 129. Visual meteorological conditions prevailed, and the flight operated on an instrument flight rules flight plan. The flight originated from Ted Stevens Anchorage International Airport at about 0250 Alaska daylight time.
Damage to Airplane
Post-landing inspection revealed that most of the right inboard foreflap had detached during the event. The right fuselage sustained three separate punctures: one above the wing-to-body fairing near the main cargo area, another in the lower cargo area with a piece of flap structure embedded, and a third above the cargo door. The right horizontal stabilizer leading edge also sustained a puncture, but no spar damage was noted. The overall damage did not meet the criteria for substantial damage as defined by NTSB regulations.
Aircraft Information
The Boeing 747-400F is equipped with two trailing-edge flaps and 14 leading-edge flaps per wing. The inboard trailing-edge foreflaps attach to main flap tracks at two points and to the midflap at three points. At each track attachment location, a sequence carriage attach fitting is bolted to the aft end of a sequence carriage via a bearing. A toggle assembly, bolted to the forward end of the carriage, engages a detent in the flap track at certain positions, forming the carriage toggle assembly.
Boeing service information indicates that skewed operation of the carriage toggle assemblies on the inboard foreflaps can cause damage to the foreflap and associated components in flight. This condition is often due to worn or broken detent rollers or binding of rollers. Historical data show that such damage can lead to foreflap separation.
Meteorological Information
At the time of the incident, ATL's automated weather station reported winds from 130 degrees at 9 knots, visibility of 7 statute miles, and light rain. Clouds were scattered at 1,000 feet above ground level and overcast at 10,000 feet.
Flight Recorders
The cockpit voice recorder and flight data recorder were retrieved and analyzed by the Aviation Safety Council of Taiwan. According to the CVR transcript, the aircraft was cleared to land at about 1242, and the crew extended flaps to 20 degrees and lowered the landing gear. At about 1245, the crew selected flaps 30; approximately six seconds later, a low-frequency roar consistent with the foreflap separation was heard. The crew performed a go-around and noted changes in handling qualities. The control tower informed the crew at about 1247 that following aircraft had observed parts falling from the airplane. Air traffic control vectored the aircraft for a landing on runway 28 at about 1258. FDR data confirmed the timing and showed no pre-event abnormalities.
Wreckage and Impact Information
Examination revealed that the right outboard (No. 6) sequence carriage attach fitting on the foreflap had fractured at the bearing lug where it connects to the No. 6 carriage toggle assembly. The forward clevis of the No. 5 carriage toggle assembly was fractured at the detent roller installation. The No. 5 and No. 6 assemblies, along with the No. 6 fitting, were retained for further investigation.
During subsequent repair, China Airlines inspected the left inboard foreflap and found discrepancies in the No. 3 and No. 4 carriage toggle assemblies. These assemblies were also retained.
Tests and Research
The removed flap components were examined at Boeing's Equipment Quality Analysis laboratory under NTSB direction. The No. 3 carriage toggle assembly was intact with no obvious damage; its detent roller had slight lateral play but no binding. The No. 4 assembly showed damage and deformation on the clevis arms at the detent roller, a seized detent roller with flat spots and significant play, and minor flat spots on some rollers. The No. 5 assembly had a fractured clevis and detached detent roller; the fracture surfaces indicated ductile overstress. The No. 6 assembly was intact but had incorrect part number on one deadweight roller. The No. 6 sequence carriage attach fitting exhibited a fatigue crack approximately 0.30 inches deep in the lug, with corrosion pitting in the bore, and the remainder of the fracture was ductile overstress.
Additional Information
There is a documented history of issues with B747-400 foreflaps and associated components, leading to maintenance procedures, service bulletins, and FAA Airworthiness Directive (AD) 75-20-05. China Airlines performed the most recent AD-required inspection and lubrication on January 28, 2013. The airline's maintenance records showed that two of three recommended service bulletin work packages and all applicable Maintenance Planning Data tasks had been accomplished since November 2012. The most recent maintenance on the inboard foreflaps was a lubrication task on May 5, 2013.
During a November 2012 maintenance visit, the No. 5 detent roller was found worn out, leading to replacement of the No. 5 carriage toggle assembly with an overhauled unit. Records indicated that the No. 4 carriage toggle assembly had been replaced in August 2005 for unknown reasons. The No. 3 and No. 6 assemblies had not been replaced since aircraft manufacture.
Following the incident, the Civil Aeronautics Administration of Taiwan audited China Airlines' maintenance program and found it in compliance with Boeing MPD requirements and the service bulletin. However, a discrepancy was noted in the recording of the overhaul on the No. 5 carriage toggle assembly, though the overhaul itself was performed according to the component maintenance manual.