Originally Posted by
asyncio
As I understand it, In all cases, if you have an empty tank selected, then the engine will suck air until you select a tank with fuel, and which point it must recover without an air lock developing.
The gotcha with both is that if one tank runs empty, then it can continue to suck air from the empty tank even if the other one is full. In which case you just do the same as in the L/R only aircraft, switch to the tank with fuel still in it.
I can only assume there were enough cases of people getting confused that it was decided that something must be done. I have seen that possibility mentioned in at least one Pup accident report.
That has always been my understanding of the reason for the rule in CS.23
G