The Navy has found what appears to be the strongest clue so far in the search for the Malaysian Airlines passenger jet that vanished 31 days ago. Operators of the Navy's Towed Pinger Locator detected two acoustic events that could have been from Flight MH370's "black boxes" in the northern part of the search area Sunday about 950 nautical miles northwest of Perth in waters nearly three miles deep. The first signal lasted more than two hours, and a second signal went on for 15 minutes as the locator was being towed by the Australian military vessel Ocean Shield, Australian Air Chief Marshal Angus Houston told a news conference Monday. "We cannot confirm pings are from MH370 until we have wreckage," Houston said. "But the signals were consistent with those emitted by aircraft black boxes." The race to locate MH370's pings is running on borrowed time, as the black box's battery is rated for 30 days. Despite being encouraged that the search efforts "are very close to where we need to be." Houston stressed caution and patience. "It could take some days before the information is available to establish whether these detections can be confirmed as being from MH370. In very deep oceanic water, nothing happens fast," Houston said. As the Ocean Shield continues passing over the area to get a better fix on the sounds' origin, Commodore Peter Leavy of the Royal Australian Navy said if the Ocean Shield crew detects the signal a third time, "that will be the trigger to launch the underwater vehicle with the sonar" to explore for wreckage.
That would involve the Navy's autonomous underwater vehicle, Bluefin-21, an unmanned submarine with side-scanning sonar that can map out the ocean floor. However, it can't detect the pings, so it needs a narrow search area. Cmdr. William Marks of U.S. 7th Fleet said the pinger locator was only about 300 meters deep when it began detecting pings at one-second intervals, well above the optimal search depth where a black box would typically be detected. The Navy switched off as much noise-producing equipment as possible to reduce the chance of false alarms and lowered the locator to about 1,400 meters. The crew was able to detect a stronger signal for a two-hour stretch before it faded. "That is actually encouraging news because as you move toward it, the signal gets stronger and as you get away from it, it should get weaker," Marks said. "Overall, we are cautiously optimistic at this time." Crews then performed a course change and passed back over the area. Crews were able to pick up a signal for about 15 minutes, he said. The two signals came from two slightly different locations. Marks said this could be an indication the both of the aircraft's black boxes were still active. However, until search crews "can reacquire the signal and use the Bluefin-21 side-scan sonar to get a picture of any potential wreckage, it is still not conclusive data," Marks said. "The 24-hour operation and the Navy team is working around the clock with our Australian partners to reacquire the black box signal." The Ocean Shield arrived in its assigned search area April 4 amid concerns that aircraft would have to spot a debris field before the pinger locator could be deployed because it's search diameter is only about a mile and it must be towed at less than three miles per hour. To date, the Navy's two P8 Poseidon patrol aircraft and a P3 Orion previously supporting the search efforts have combined for 24 missions with 220 hours of flight time covering 336,000 square nautical miles. The Malaysian jet disappeared early March 8 with 239 people aboard en route from Kuala Lumpur to Beijing. The United States is among 26 countries aiding in the search.