Thats been a problem ever since i started playing this game.
Theres one surefire way that i know of. Get close to a field that has a runway reaching the waterside. Then go sull speed and beach your PT on the runway. This will do some damage, but provided your on the tarmac you get a landed successfully.
Besides that, technically close to CV/Tsk group and at the spawns should get a successfull landging too. But thats rather unreliable - best you try it out offline or in the TA what works and what not.
One thing you have to make sure is: You have to have stopped moving/drifting completely, otherwise you get a ditch.
I know this is not really helpful, but its all i can tell you about it.