Fuselage Cracks, Poor Maintenance Cited in 2002 Rupture of B747

Air Safety Week, March 7, 2005

The Deadly Tail-Strike Strikes Again

Above and beyond the aging of airframes and normal wear and tear on structural components, there are valid concerns with accumulated and hidden misrepaired damage. The absolute importance of structural integrity in the pressure vessel has been graphically demonstrated by the final accident report on China Airlines Flight CI-611 that broke apart over the sea between Taiwan and Hong Kong in May 2002.

The investigating body, the Aviation Safety Council (ASC) of Taiwan, in a report released on Feb. 25, blamed cracks in the plane's fuselage as well as poor maintenance for the crash that killed all 206 passengers and 19 crew on board.

The ASC concluded after a two-year investigation that a roughly six-foot crack in the fuselage caused the in-flight breakup. The accident aircraft had suffered a tailstrike during landing in Hong Kong 22 years earlier, and a temporary repair was apparently the only repair done to the damage. ASC could find no evidence of a permanent repair, even though after such a strike, it would have been required by manufacturer Boeing [BA].

ASC found evidence of heavy corrosion beneath the doubler that was installed to repair the tailstrike. Although ASC -- Taiwan's equivalent to the U.S. National Transportation Safety Board -- could not confirm exactly how the fuselage came apart, it criticized the air carrier for not finding the damage to the aging aircraft in regular checkups over its 23-year lifespan.

CAL officials, however, rebuked the ASC's report and questioned its findings. "Since the section of the aircraft that is suspected of causing the crash was not found, the information is not conclusive enough to determine the exact cause of the accident," CAL said in a statement. "The ASC said that they have found 75 percent of the aircraft, but they actually collected only 50 percent of the damaged Section 46, the key part needed to determine the cause of the crash," said CAL spokesman Roger Hen.

The air carrier also objected to ASC's claim that maintenance oversight was to blame. "Our checkups are conducted in compliance with the SRM [structural repair manual]. Boeing stated clearly that if repairs are done in accordance with the SRM, there is no need to report it to the aircraft manufacturer," Hen said.

According to Boeing's Repair Assessment Program (RAP), that aircraft should have undergone inspections upon reaching 22,000 flights. Yet the accident occurred when the jet completed its 21,398th flight, a few landings short of the maintenance program's maximum threshold.

The Taiwan Civil Aeronautics Administration (CAA) also slammed the ASC report, accusing the agency of failing to find the actual cause of the crash. "How could the ASC jump hastily to its conclusions when half of the [section in question] has yet to be found?" asked CAA Director-General Billy Chang.

Important wreckage never recovered

Flight CI-611, a Boeing 747-200 (Reg: B18255), crashed into the Taiwan Straits 23 nautical miles NW of Makung, Penghu Islands off Taiwan, Republic of China (ROC) on May 25, 2002 (ASW, June 30, 2003). The aircraft was flying from Taipei to Hong Kong (HKG), and radar data indicated that the aircraft experienced an in-flight structural breakup at 35,000 feet.

The last "paint" of CI-611 received from Makung radar was at 07:28:03UTC, at 34,900 feet. The aft fuselage section was recovered earliest along the track, the upper forward fuselage next and the engines were furthest along the track. The cockpit voice recorder (CVR) and flight data recorder (FDR) were recovered 25 days after impact in 50 to 70 meters (roughly 200 feet) of water. During the debris retrieval period, three typhoons disrupted the effort. Salvage was conducted in four phases with the final phase involving a formation trawl for pieces embedded in the sandy bottom. The entire wreckage recovery operation lasted five months, recovered approximately 1,500 pieces, and 78 bodies. However, a large portion of the important aft fuselage (Section 46) remains unrecovered.

The FDR stopped recording at 07:27:58.9 UTC (at 34,573 feet), and the last transponder beacon reply was received at 07:28:03 UTC (34,900 feet, by Makung site). FDR data from other aircraft on the Hong Kong route disclosed that the wind profiles had been fairly slack all the way up to CI-611's cruise height. There was no carbon remains found on any of the recovered bodies or their clothes. No signs of burning or blast damage were found. Injuries were consistent with an explosive decompression. The condition and position of the hinge and door mechanisms indicated that the forward cargo door did not open prior to the airplane's breakup. The aft cargo door was retrieved in three major segments. The upper portion of the door was recovered with the hinge intact and the actuators in the closed position.

Examination of the hinge, latches, and door mechanisms indicate that the aft cargo door did not open prior to breakup. The Section 46 structure was distributed over a large area, extending more than four miles East to West. The investigators' comprehension of the progressive breakup process was aided by paint transfer to and from cabin structures (such as seats) and the empennage assembly (such as fin and horizontal stabilizer leading edges), as well as wreckage distribution patterns.