"If they have a strong feeling or indication that the debris belongs to the aircraft, one of the first things authorities will do is drop sonar buoys in the water. If the black box (flight recorder) is there, the buoys should be able to pick up the signals. This could take up to 48 hours but it all depends on how near or far the ships and other assets are."
January 1, 1970
https://en.wikiquote.org/wiki/Malaysia_Airlines_Flight_370