Fuselage Cracks, Poor Maintenance Cited in 2002 Rupture of B747

Air Safety Week, March 7, 2005

The 22-year-old tailstrike

On Feb. 7, 1980, the accident aircraft suffered a tailstrike during landing in Hong Kong. A preliminary inspection at Hong Kong found abrasion damage on the bottom skin of the fuselage tail between STA 2080 and 2160, and between STA 2578 and 2658. The aft drain mast was missing. The left outflow valve door inboard corner was partially cut. There was no structural repair conducted at HKG. The damage assessment or evaluation report of the specific damage at HKG was unavailable. According to the CAL flight engineer report, the aircraft was ferried back to Taipei. CAL could not provide the aircraft release information according to the Aircraft Flight Operation Procedures of the Taiwan Civil Aeronautics Administration (CAA) in 1976, which state, "Article 45 -- A maintenance release shall be completed and signed off by a certified mechanic and the personnel shall certify that the maintenance work performed has been completed satisfactorily with the Maintenance Control Manual."

Regarding the temporary repair to the tailstrike, the Boeing Field Service Representative (FSR) at Taipei advised Boeing that China Airlines had accomplished a temporary repair consisting of temporary aluminum skin patches. He further advised that China Airlines intended to complete a skin replacement or external patch permanent repair per the structural repair manual (SRM) at a later date (but within four months). ASC could find no record that indicated Boeing was advised that the permanent repair had been completed.

Crash problem area also in the aft fuselage

The recovered portions of the semi-monocoque structure (skins/frames/stringers) in Section 46 were arranged on a reconstruction jig to assist in evaluating the fractures and deformations of the panels. A field examination was conducted on the fracture faces. Item 640 -- the 640th piece of wreckage recovered -- was found to have flat-fracture surfaces (indicative of slow-growth fatigue mechanisms) on the skin adjacent to an external repair doubler. The doubler measured about two by 10 feet. No slow-growth mechanisms were noted on the remaining skin segments in Section 46. Many of the rivet shanks attaching the doubler were projecting beyond the approved stem length (i.e., the substandard riveting being over- or under-driven).

The fracture directions show the crack progressed under the belly of the airplane and then continued forward along stringer S-50R. The crack then progressed upward at approximately STA 1900. The direction of the fracture propagation was based on hole-to-hole cracking patterns, chevron marks, and branching cracks. The entire empennage separated from Section 46 forward of the aft pressure bulkhead at STA 2360. Separation of the empennage structure resulted from a combination of impact from the Section 46 structure and insufficient remaining Section 46 structure to support the weight and loads of the empennage. The empennage impacted the water relatively intact.

All engine pylon fuse-pins were found intact with engines impacting the water still attached to their associated pylon structures. Further metallurgical field examination of recovered structural items of the fuselage Sections 41, 42, 44 and 46, as well as the outboard and center wing sections, and keel beam were carried out. All fractures examined were characterized as being due to various modes of ultimate ductile separation (i.e., instantaneous tension, shear, compression, bending). No other evidence of any slow-growth cracking mechanisms or pre-existing corrosion was observed.