Another "expert" is now being quoted in the
New Straits Times
According to him, the Under Water Beacon (ULB) can emit a signal for hundreds of miles but if the black box is covered with debris or falls into a trench at the bottom of the sea, then the strength and range of the signal would be lower.
For the record a Towed Pinger Locator (TPL) can only be expected to detect an operational ULB 37.5kHz signal when no more than 2 - 3km from its source. Ninety percent reliability is around 1,800 meters, and water temperature inversion layers can often create a variable outcome.