I had a thought after hearing another report on the failure to locate the missing Malaysian airliner. It seems so obvious to me I can’t see why it hasn’t been implemented before, but I can’t recall hearing of such a thing.
The idea is to distribute about the airframe a bunch of small buoyant mini-beacons. I imagine them being about the size of tennis balls, but maybe bigger would be better. They would be activated either by immersion in water or by experiencing extreme shock. Each would then transmit in a similar way to Breitling’s Emergency Watch. By having enough of these at strategic points of the aircraft would greatly increase the chance that at least one will be ejected from the wreckage. That way the crash site can be found even if the plane sinks without visible trace. I know there is often some sort of locator transmitter on the black-box and cockpit voice recorder, but there is no guarantee that these will not be damaged or submerged.