(CNN April 8,2014) — The optimism that bubbled up over the weekend when an Australian navy ship detected pulses that appeared to signal the nearby presence of Malaysia Airlines Flight 370’s so-called black boxes had subsided somewhat by Tuesday, as continuing listening efforts yielded nothing.
Searchers are still scouring the waters, but their optimism is “more cautious,” said U.S. Navy Cmdr. William Marks. “As hours pass,” he said, “our optimism is fading away, ever so slightly.”
His restraint contrasted with the cheers that erupted Saturday when the team aboard Australia’s Ocean Shield detected a possible signal from the plane’s flight data recorder or its cockpit voice recorder. A second possible signal was heard soon after.
The signals, detected about 1,100 miles (1,750 kilometers) northwest of Perth, Australia, were consistent with those sent by a flight data recorder and a cockpit voice recorder, retired Air Chief Marshal Angus Houston said. They were heard in seawater about 14,800 feet (4,500 meters) deep.
nvestigators hope the signals were from locator beacons that were attached to the data and voice recorders that were stored in the tail of the Boeing 777-200ER when it disappeared from radar screens on March 8.
“The audible signal sounds to me just like an emergency locator beacon,” Houston said. “We are encouraged that we are very close to where we need to be.”
If the signals are heard again, searchers could deploy an underwater drone to take photos to determine whether they do mean the discovery of the black boxes. That process could take more than a week.
“Until we have stopped the pinger search, we will not deploy the submersible,” Houston said. “We will not deploy it unless we get another transmission in which we’ll probably have a better idea of what’s down there.”