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By Michael A. Dornheim/Aviation Week & Space Technology
03-Jun-2002 11:40 AM U.S. EDT
LOS ANGELES -- Investigators of last week's top-of-climb disintegration of a China Airlines Boeing 747-209B are engaged in a month-long effort to retrieve 80% of the wreckage.
Major pieces of the airplane and the black boxes were located last week in the Taiwan Strait but not immediately recovered because of strong currents and high seas. At least 92 bodies had been found in the water by late last week, and the 209 passengers and 16 crew are all presumed dead.
The unusual accident with no obvious cause raises anxiety in a region that's home to many 747s and has an accident rate that varies greatly among carriers. Memories of the TWA Flight 800 inflight fuel tank explosion in July 1996 linger, especially since the ignition source was not definitively found.
China Airlines Flight 611 took off from Taipei's Chiang Kai-Shek International Airport at 3:08 p.m. local time on May 25, heading southwest on a 1.6-hr. flight to Hong Kong. Twenty minutes later, the final radar transponder signal indicated 33,500 ft. altitude, then died at 3:28 p.m. The skin echo broke into four separate track groups on a military radar. There were no distress calls; the crew talked to air traffic control at 3:16 p.m. to confirm they were cleared to 35,000 ft., and that was the last message heard from them.
The recorders were found at 23 deg. 35 min. N. Lat., 119 deg. 24 min. E. Long., where the ocean is 40-80 meters (130-260 ft.) deep. Near that location searchers using sonar also found a large piece of wreckage about 130 X 30 ft. in size.
The Aviation Safety Council (ASC) of Taiwan is conducting the investigation. The U.S. NTSB sent a five-man team headed by Greg Phillips as the accredited representative, and the FAA sent three people. Boeing and Pratt & Whitney personnel are also at the search headquarters at the Makung region on the Penghu Islands several miles east of the accident area. Information is being posted on the ASC Web site at
www.asc.gov.tw.
The air traffic controller following Flight 611 noticed the data line indicating actual altitude disappear at 3:28:03 p.m., and the entire signal disappeared on the next radar sweep, said Kay Yong, managing director of the ASC. The controller called Flight 611 repeatedly but was unable to raise them, and other controllers were not able to find the aircraft. The civil radar does not have the power to detect primary skin echoes, Yong said.
The Taiwanese military provided the ASC with primary radar data. They show the aircraft moving at about 430 kt. on a 226-deg. ground track, then breaking into four track groups. Curiously, one of these groups moves in the opposite direction of 50 deg. at a speed of several hundred knots, Yong said. It is not yet clear whether this is a radar anomaly or the actual motion of the objects. The military data are not individual skin echoes but fused tracks based upon several radars, and so far the military has been reluctant to discuss radar algorithms that could cause strange results, e.g., from the many echoes of a cloud of debris. The viewing geometry may also give some speed ambiguity on short-duration tracks.
"We can't assess the possibility of a midair collision right now," Yong said. "We need more radar data." Through the NTSB, the ASC has asked the U.S. Defense Dept. if it has any radar data covering the accident. It is asking the same of China, and would like helpful satellite pictures as well.
The sound beacons from the flight data and cockpit voice recorders were located on May 29, but ocean currents were too strong to retrieve them with divers or a remote-control submersible. The currents vary daily. A boat was keeping a round-the-clock vigil on the recorders in case the current moved them. Fishermen say there are small local ocean floor trenches in the area. The batteries for the sound beacons should last 20-30 days.
The wreckage found nearby is believed to be a piece of the fuselage. A boat used its anchor to scratch the metal and found green zinc chromate primer paint, indicating it is an aircraft part and not other debris. High currents prevented recovery late last week. Pieces already recovered include a trailing-edge flap and the leading edge of the vertical stabilizer.
"Personally, I think the wreckage is more important than black boxes," Yong said. He aims to retrieve 80% of the wreckage in 30 days and reconstruct it on the Penghu Islands, but as of late last week he estimated that less than 1% of the wreckage had been recovered. The ASC has engaged Massachusetts-based American Underwater Search and Survey Ltd. to help with recovery. The company worked on the TWA Flight 800 recovery. The search area on May 28 was 16,129 sq. km. (6,230 sq. mi.), according to Transportation and Communications Minister Lin-shan Lin. Fortunately, northwest ocean currents tend to push wreckage away from a 150-200-meter-deep oceanic trench.
The recovered bodies are mostly intact but with broken bones. There has been no sign of a fire in the bodies or the debris so far, Yong said. At 33,500 ft., Jet A fuel would be flammable from 135F down to 60F or lower, and it is plausible that the fuel would still be in this temperature range just 20 min. after takeoff (AW&ST July 7, 1997, p. 61). It is not known yet what type of fuel was in Flight 661.