In the latest sliver of hope that the missing Malaysia Airlines Flight 370 might be found, a ship in the search area has heard a "pulse signal" like the one emitted from the plane's black box.

Monday will mark Day 30 since the plane disappeared, and with it the end of one of our best hopes for finding it. The plane's black box sends signals, but only as long as it has battery power. That power will run out around Day 30. The U.S. Navy deployed a specialized Towed Ping Locator yesterday, which can detect pings from up to 20,000 feet below the surface, in the hopes of finding the black box in time.

Yet it was black box detector on the Chinese ship Haixun 01 that picked up a possible signal, state-run news agency Xinhua reported. The signal is the same frequency as that used by black boxes -- 37.5 kHz -- which is a good sign. But this is, of course, no guarantee that it's coming from the plane. Here's why:

  • There have been countless possible plane sightings that have not panned out over the last month, from oil slicks to ocean garbage. This could just be another one.
  • Neither Australia nor the United States have been able to verify Xinhua's report yet.
  • The British HMS Echo thought it heard something from the black box a few days ago, but it was a false alarm. These can be triggered by whales or interference from other ships. Chinese officials have been careful to say that there is no proof yet that the signal is from the plane.
  • CBS News' transportation safety analyst Mark Rosenker seemed dubious that the signal came from the plane, noting that there should have been plane debris near the site of the signal. "It defies logic that we would not be seeing something on the surface," he said.
  • It took two years to find the black box from Air France Flight 447, which crashed into the Atlantic Ocean in 2009, and we knew where that plane went down.