搜索马航失联飞机的重点区域

WASHINGTON — After several days of searching there is still no sign of the Malaysian Airlines jet that disappeared Saturday with 239 people on board. Flight 370 took off from Kuala Lampur bound for Beijing, but disappeared somewhere over the South China Sea.

Ten countries, 20 airplanes and more than 40 ships, including two U.S. destroyers, are combing the South China Sea. Still, no clues have emerged as to how a state-of-the-art airplane could just disappear.

“At the moment, we don’t have answers. But it’s important that we are out there, looking,” said Australian prime minister Tony Abbott.

The flight took off in good weather from Kuala Lumpur, en route to Beijing.

Now, the Malaysian government is expanding the search beyond the 92-kilometer radius from where the last contact was made.

“We are looking at every angle,” said Azaharudin Abdul Rahman, Malaysia’s civil aviation chief.

Investigators are searching for two key pieces of evidence. The first piece is the plane’s black box -- which is actually bright orange to be visible in crash debris. Its two parts -- the flight data recorder and the cockpit recorder -- would provide investigators with a record of electronic instructions and any cockpit discussions prior to impact. However, the black box only emits a signal for 30 days.

“It’s a little audio pinger that’s in that black box, that is sending out a signal that says, ‘I’m here, come find me.’ The clock is ticking. Thirty days to go, or we lose that pinger,” explained Stephen Ganyard, an aviation consultant.

The box has an underwater beacon that can transmit at a depth of 4,000 meters.

The second key to the investigation is any debris that would provide a clue about what happened. Many point to the lessons learned after TWA flight 800 crashed into the Atlantic Ocean in 1996.

"The debris from TWA 800, which was originally thought to be [caused by] potentially a bomb on board, turned out to provide enough information to point to a different type of explosion," said aviation expert Vahid Motevalli via Skype.

Four years after the crash, U.S. investigators ruled the cause was aircraft malfunction.

No one knows what happened to Malaysian flight 370. Experts say until authorities find either the black box or crash debris, it’s all speculation.