Above and Beyond... Nearly - S5-E20
Continuity mistake: After Station 51 is dispatched to 'man stranded on a cliff', when Roy and John free climb up the cliff, they're not wearing their uniform shoes, they're wearing hiking-type shoes with ridges on the soles.
Answer: I believe you are speaking of the old man, Mr. Wilson. He's played by J. Pat O'Malley.
Bishop73
Correct, it was J. Pat O'Malley...he also played the grandfather with his grandson when their rocket exploded, and also played "Old Bill" in the episode with Ann Prentiss, where Gage saves the little girl from the burning tree house, and her mother falls in love with him.