Underwater search teams in the Indian Ocean have picked up two fresh signals that they hope are from the black boxes that were on board the missing Malaysia Airlines Flight 370.

The searchers have now found four signals total — all within 17 miles of each other. Authorities are almost certain this could be their big break.

"I'm now optimistic. We'll find the aircraft or what's left of the aircraft in the not too distant future," Air Chief Marshal Angus Houston said Wednesday.

With a pinger locator in tow, Australian ship Ocean Shield first detected signals over the weekend that were consistent with those from a flight data recorder and a cockpit voice recorder. At the time, authorities said it was their "most promising lead." But after they lost the signals, it was nothing but silence for three days. It seemed they'd hit another brick wall.

Then, two new pings. The first signal lasted 5 minutes, 32 seconds; the second was 7 minutes.

These new signals are in the within the confines of a small search area that's about 1,100 miles from Perth.

"I believe we are searching in the right area, but we need to visually identify wreckage before we can confirm with certainty that this is the final resting place of MH370," Houston said in a news conference.

Image: Australian Maritime Safety Authority

After chasing down several dead-end leads over the past month, authorities approached the first rounds of signals with skepticism because marine life can sometimes emit similar sounds. However, experts analyzed the first two signals and determined that they were, in fact, from a manmade device and not nature.

Up to 11 military aircraft, four civil aircraft and 14 ships are assisting in Wednesday's search. The underwater search is also in progress, with Ocean Shield at the northern end of the search area and HMS Echo and Chinese ship Haixun 01 to the south.

Image: Australian Maritime Safety Authority

If teams recover the plane's black boxes, it will be nothing short of a miracle. Batteries in the flight recorders last only 30 days. As of Wednesday, the plane has been missing for 33 days.

If the signals disappear before officials locate the flight recorders, we may never know what happened to MH370.

Timeline of the search for MH370