Paulo,
If in doubt - get out of harms way and talk about it later.!!!!
When you have and engine failure do you sort out the aircraft and make an R/T call or do you make the call and then sort out the aircraft?
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einglshal,
This has nothing to do with ATC and I hope that I can rest assured that if one had doubts about an situation involving ATC that everyone would address the question to ATC and not to the other aircraft on frequency.
FISO and Air Ground Radio and for that matter ATC radio frequencies are for Air - Ground - Air communication. They are not for Air to Air communication.
The crux of this argument lies with the fact that Paulo had the other aircraft in sight and had the ability to ensure the safety of his aircraft (and the other aircraft).
If however, Paulo was observing an imminent collision between two other aircraft (who may not see each other) then he would be quite correct to issue a warning on the R/T. But I bet that he would be disapointed if after issuing the warning, the aircraft in possible danger did nothing other than make a radio call asking the other aircraft if his aircraft was in sight.
Regards,
DFC