BRENT HANNON / TAIPEI & NICHOLAS IONIDES / SINGAPORE
Safety council says cracks and corrosion developed on patch on pressure hull
Investigators probing the May 2002 break-up of a China Airlines (CAL) Boeing 747-200 at nearly 35,000ft (10,675m) are focusing on whether a sudden decompression was caused by the failure of a repaired section at the aft fuselage of the aircraft.
Although Taiwan's Aviation Safety Council (ASC) has released an interim "factual data collection", it does not include conclusions on the cause. A final report is due to be published before the end of 2004.
The aircraft crashed into the Taiwan Strait, killing all 225 people on board. Its hull was tracked on radar breaking into large sections that fell separately in the aircraft's climb to 35,000ft. No evidence was found of fire, smoke or explosives.
ASC investigators rule out engine malfunction, bad weather, air traffic factors, security and pilot error. They are now concentrating on a repaired section at the tail of the aircraft. The council said, when it released more than 700 pages of data last week, that cracks and corrosion developed beneath an aluminium repair doubler, or patch, that was installed on the pressure hull following a February 1980 tail strike on landing at Hong Kong.
"It is clear that there was overload on the doubler," says ASC managing director Kay Yong. He said of the fatigue cracks: "Some penetrate the structure, and some penetrate partially."
Investigators have checked the position of pressure-equalising panels in the main-deck floor between the passenger cabin and cargo hold, to determine if there was a sudden loss of pressure in the cargo hold. "If there is a pressure difference, these panels will open. Four popped open, all of them in the rear of the aircraft," says Yong.
Damage from the 7 February 1980 tail strike included: abrasion damage; a missing aft drain mast; and a partially cut left outflow valve door inboard corner. CAL says it performed two repairs: a temporary repair on 8 February 1980 and a permanent one in May that year.
The report says Boeing's Hong Kong office recorded the fact that a temporary repair was being made using a different aluminium specification to the pressure hull. But Boeing at Taipei was not consulted over the permanent repair that CAL said was done but for which no detail exists.
CAL notes that "there was no regulation requiring retention [of] the records for more than two years" and stresses that "it is not known if this fatigue is related to the cause of the accident".
Source: Flight International
