Originally Posted by 500N
The problem is of course finding those first bits !
The Towed Pinger Locators (TPL's) are to detect the Underwater Locator Beacons (ULB's) - one attached to the DFDR, and one attached to the CVR. They have a guaranteed battery life of 30 days, but the manufacturer will probably ensure that is extended to about 40 days. In the AF447 case, neither worked, and one was never found.
The ROV option is only useful when you have found something worth taking a look at. Initially, and if the ULB's are not located, a dedicated underwater search plan needs to be drawn up based on the best information available. In the MH370 case, the area selected to search will probably not be less than that which was searched using Autonomous Underwater Vehicles (AUV's) to find AF447, in which case this whole operation will take not weeks, but many months if not a year or more.
Why? The backtracking of surface floating debris is not a precise science, and the "butterfly effect" created by spurious vortexes that spin stuff off and then repeat the process, tends to confuse the issue.
Don't hold your breath.
