I was once on a VFR flight on a very nice sunny day and was under RIS. I got a call telling me of traffic directly ahead of me 3 miles, no height information. I looked and looked but couldn't see anything. A minute later a call came in telling me it was now 1 mile ahead, I looked everywhere but still couldn't see it. I was getting a bit concerned at this point as I am usually quite good at spotting others so I kept scanning the sky ahead, to the sides and even slightly behind. Suddenly I looked straight UP and saw a glider not very far away flying in exactly the same direction at about the same speed
, from the ground it would have looked like we were flying in formation. I made an immediate course and altitude change as the glider pilot would never have known I was there.
If it hadn't been for the constant RIS notifications, even though their distances were slightly out, I MAY have never seen the other aircraft.
Draw from this what you will.
Skyhawk.