Some insights from an ex-RAAF P3 pilot.
As one of the ex P-3 people with experience of searching for things in the Southern / Indian Oceans I thought I might be able to contribute some informed comment on this thread.
Re the P-3 endurance - it is not crew duty but engine out depressurized considerations (3 engine 10,000' cruise) that is the real limiting factor. You have to base everything on returning to Perth / Pearce. We were able to fudge this a bit by using a tailwind component on some flights but you don't actually know the 10,000ft winds so you don't want to get too greedy. There are also issues with loitering engines which is a normal P-3 procedure to extend time on station. Because of the risk of a prop overspeed on a restart you need to be able to start the engine at some altitude with a relatively high TAS or the drag could be really high and you will end up in the drink off SW WA. If there are icing conditions, even a thin layer of cloud can cause a loitered engine to ice up in a flash - can take days to thaw out the solid lump and you are struggling to get back to PER / PEA so you won't loiter. With a limited on station time the benefits of loitering are small and while the risks of a malfunction during engine shutdown are small as well you have to decide if it is worth it. In my series of searches very few captains loitered engines and then only when the weather was clear enabling hi alt shutdowns and restarts.
If the crews are on the ball they will be taking off overweight, using true cruise climbs to on station (i.e set max cont engine temp and max range cruise speed and slowly climb continually) and using min operating reserves (15 mins fixed and no variable). However, to get more than three hours on station would be great going. You actually land with plenty of gas because of the 3 eng 10 considerations.
Re the search
Objects will be very hard to spot!!!! Especially if they are awash.
I was asked by an artist to describe the colours I observed so he could do a painting of one of the yachtie rescues. He painted it but when I described the colours you could see is heart sink - I told him we were in a grey aeroplane over a grey and choppy sea with grey cloud and a hazy grey horizon. We spotted one sailor visually but what we spotted was him standing on the top of the cabin of his sinking yacht which was awash - it was the contrast (he appeared black) which made him visible and we had a beacon location accurate to about 5nm enabling a dense sector search over a reasonably low sea state (3 - 4) and about 2 - 3 mile vis. The other two were radar homings to upturned yachts which stuck above the surface and made good radar and infrared targets - and we had reasonably recent satellite beacon positions to go on. (N.B. none of them had proper EPIRBS but used a French tracking system where the beacons only sent signals intermittently for short periods). You couldn't make them out visually until fairly close as they were white hulls in very angry seas with lots of white wave crests, sea spray, etc; even though they were sticking well out of the water. I did 4 missions searching for stuff down there and the weather was never good and one of the most striking features was how the conditions changed rapidly with time and over small distances.
With any potential MH370 wreckage, there won't be much temperature contrast to help infrared and if the sea state is up, picking out a radar target against sea clutter will be hard (although both the radar and IRDS are better than in my day). I think the best chance is for any items picked up on satellite to be quickly passed to the crews so they can narrow the area of probability. This will be difficult as detecting and interpreting any images may take some time. I hope it is quicker than AMSA passed on satellite beacon data when we searched for the yachties (it was 17 years ago but the importance of speed in transferring the info was one of our biggest debrief points to AMSA). At least they should start to be getting some actual drift rates from beacons and buoys that will have been dropped which should help, and awash objects shouldn't have high wind drifts to complicate the issue.
I can understand sending HMAS Success down there as it is a versatile ship with the ability to lift and store items out of the water - carry a decent helo, etc. However, I would love to see an ASW ship (ie an ANZAC class) and better yet a submarine heading South to search for the data recorder beacons (in the predicted flight path) - their batteries will only last a couple more weeks at best. While the area is large making detection probability low, detecting the beacons is the best way of speeding the time and reducing the cost of finding and recovering the recorders.