Elusive 'black boxes' slow crash investigation

TAIPEI, Taiwan -- Strong, shifting currents have frustrated efforts to find the "black boxes" from a China Airlines jet that broke up high over the Taiwan Strait, killing all 225 people on board.

For the second time since Saturday's crash, investigators announced they had picked up beacon signals from the black boxes -- or voice and flight data recorders -- only to announce hours later that they were mistaken.

Taiwan's military earlier dismissed the possibility the plane broke up at 30,000 feet (9144 meters) because it was hit by a Chinese missile.

After two days of searching the rough waters of the Taiwan Strait, investigators have few answers about why 747 jetliner crashed into the sea.

David Lee, the lead investigator for Taiwan's Aviation Safety Council, said the strait's strong currents have complicated the search and might have carried the black boxes away from where officials thought they were.

CNN NewsPass VIDEO CNN's Mike Chinoy reports on efforts to recover wreckage from the crash of a China Airlines jet in the Taiwan Strait. Play video   MORE STORIES Crash unites Taiwan, China in common cause    ANALYSIS China Airlines' troubled history    AUDIO The press is rife with complaints about Taiwan's poor aviation safety record 1.25 MB / 59 secs WAV sound   EXTRA INFORMATION Timeline: Major air disasters in Asia     CNN.com Asia More news from our Asia edition

The Associated Press reported Lee as saying the signals might have come from the dozens of ships searching for bodies and the wreckage of the Boeing 747-200.

He also said he doubted the recorders were damaged because the devices are rugged and designed to survive some of the worst accidents.

The black boxes -- which are actually bright orange -- might offer the best clues to why Hong Kong-bound Flight CI611 split into four pieces 20 minutes after taking off from Taiwan's Chiang Kai-shek International Airport in clear weather.

Taiwan's aviation officials say they will ground all remaining models of the plane, a Boeing 747-200, until the cause of the crash is determined.

Missile theory shot down

Investigators have declined to speculate on the cause of the crash, and security officials said there was no evidence the plane was brought down by a terrorist or missile attack.

"Communist China has denied it. We think its denial is highly credible," a military spokesman told Reuters news agency, responding to a report on cable news network Formosa TV which quoted an unidentified military analyst as saying a Chinese missile may be to blame.

"Based on our own judgment, we can also say it's absolutely impossible," the spokesman said, adding that Taiwan's military was not conducting any exercises or missile-testing in the area at the time of the crash.

Taipei and Beijing have been bitter rivals since their split at the end of the Chinese civil war in 1949. Beijing views the democratic island as a breakaway province that must be returned to the fold, by force if necessary.

One theory is that structural problems caused the break up of the 22-year-old jetliner, which the airliner planned to retire from its fleet next month.

Another theory is that the plane's cargo or fuel tanks exploded, causing it to break up. Radar showed that one chunk of the jet shot backward at a high speed, as if propelled by a blast. The other three parts kept going forward.

On last journey

But so far, most of the pieces of wreckage have not showed signs of burning. Lee said it was too early to rule out an explosion, however.

"The wreckage we've found so far is not major portions of the plane," he said.

"Whatever it was, an explosion, a structural failure, I can't tell at this point," Lee added.

Fishing boats and naval vessels have so far plucked about 80 bodies and several pieces of wreckage from the rough waters.

The China Airlines crash is the fourth fatal crash for Taiwan's leading carrier in the last decade. (Full story)

The plane was one of the oldest planes in the China Airlines fleet. The flight was supposed to have been the plane's last journey before being sold to a chartered carrier in Thailand.