You MUST be sure where ALL aircraft in a close proximity are at all times. IF you can't see it, be worried till you do. . GOOD radio and procedures is the best AID to such situations. What happened to radio checks? Frequent operations at low level in a salt environment more so, Corrosion. I've flown with 5 No radio U/Ls in the SAME circuit and that's about saturation for me and quite tiring. Overlapping intersecting Circuits Are Russian Roulette requiring extreme caution. Nev