[Beery]

As far as I can see the plane is about 4km away. I've been airborne in a WW2-era aircraft and the thing vibrated so much that I was lucky if I could see a battleship at 4km, let alone a sub, even if I knew it was out there somewhere. At under 1000ft (which seems to be about how high planes fly in the game) a sub 4km away is a tiny speck near the horizon. A pilot is not going to see it unless he's pointed directly at it because your view from most WW2 cockpits is obscured by wings to the sides and the fuselage to the rear. Remember, subs are camouflaged, these planes don't have radar and most planes flying over your position aren't even looking for subs. The other problem is that in a vast featureless ocean the brain plays tricks - after hours in the cockpit looking at a grey expanse of sea a pilot might not notice a sub even if he's looking right at it.

I think players sometimes tend to have seriously unrealistic expectations of what human beings are able to do. Even if the plane was actively looking for your sub (which may not be the case), even if he knew your general position (he doesn't), the chances are still fairly low that he's ever going to spot you unless you're right in front of him.