How ping signals are helping to narrow search area for Flight 370

The search area for missing Malaysian Airlines Flight 370 has narrowed dramatically - shrinking by 7 thousand square miles.

The hunt for a Flight 370 ping: How they are doing it

A search plane has detected a possible signal - the fifth so far - from the locator beacons from the missing jet's so-called black boxes, the Australian agency coordinating the search announced.

Officials say each new signal is helping them zero in on the once sprawling search area.

CNN's Tom Foreman explains how signals are helping to narrow down the search area for Flight 370.