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Searchers for the missing Malaysia Airlines Flight MH370 must gear up their hunt for the aircraft's black box, an aviation expert said as an Australian ship carrying equipment to locate the device set sail on Monday.

It is presumed that the black box will run out of battery power around April 7, or April 12 at the latest, and its signal will then vanish, said Wang Ya'nan, deputy editor-in-chief of Aerospace Knowledge magazine.

"I don't want to be pessimistic," Wang said, "but the fact is that without the signal, it will be virtually impossible to find it."

In the case of the search for Air France Flight 447, which crashed into the Atlantic Ocean on June 1, 2009, nearly two years were required for retrieval of the black box, even though the crash site was located within a week of the accident.

"The French detected the signal sent from the black box before it lost power and determined the approximate site," Wang said. "The reason so much time was needed to raise it was that the water's depth made it very difficult to finalize the precise location."

Even if every nation involved in the search put all their deep-sea submersibles into the operation, there would not be enough of them to cover the enormous swath of ocean where the small device could be, he said.

To quickly narrow the search for MH370, searchers need to find surface debris, he said.

The black box consists of two separate pieces of equipment: a flight data recorder and a cockpit voice recorder. The boxes are usually kept in the tail of an aircraft.

Each black box is fitted with an underwater locator beacon that starts emitting a pulse if its sensor touches water, meaning it "pings" once per second for 30 days before the battery runs out.

Even though Malaysian officials declared that MH370 had crashed, no physical evidence has been found, despite a massive hunt involving seven countries. The jet carried 239 passengers and 12 crew members.

Hopes raised by debris sightings have repeatedly been crushed as the items turned out to be random sea junk such as fishing gear.

Questions:

1. When is it presumed the black box flight recorder will run out of battery power?

2. How long did it take to get the Air France Flight 447 black box from the Atlantic Ocean?

3. How many pieces of equipment are in a black box?

Answers:

1. Around April 7, or April 12 at the latest.

2. Nearly two years.

3. Two.

（中國日報網英語點津 Helen 編輯）

About the broadcaster:

Anne Ruisi is an editor at China Daily online with more than 30 years of experience as a newspaper editor and reporter. She has worked at newspapers in the U.S., including The Birmingham News in Alabama and City Newspaper of Rochester, N.Y.