On Saturday, July 11, 2015 at 8:39:21 PM UTC-7, Bob Pasker wrote:
if he was in fact doing an approach at the time

the RADAR works whether you're on approach or not

I do know how RADAR works, in lots more detail than we need to get into here. But SSR surveillance only "works" in any useful collision avoidance sense if:

1. The transponders in both aircraft are on and operating correctly, (I'll skip for now any discussion about the KCHS Approach ASR-8(?) primary radar limitations/performance issues)
2. The aircraft are at a suitable height (and location) for SSR coverage for that ATC facility
3. One or both pilots are talking to approach/ATC
4. Approach/ATC provides them with some traffic warning/separation instructions, and
5. The pilot(s) are able to use that warning/instructions to avoid each other

Which is why there are lots of relevant questions about what exactly was happening, which AFAIK at the moment can only be guessed at, including.... Was the F-16 flying an approach or otherwise talking to KCHS Approach (and on VHF/UHF?)? Was the F-16 actually in IMC? Just exiting IMC? Was the Cessna 150 on flight following/talking to KCHS Approach (on the same frequency so they could hear the F-16?)? What altitude did the collision happen at? When/did the F-16 hand off from Shaw RAPCON to KCHS Approach? Were both transponders and encoders actually working correctly? What traffic warning/separation did Approach provide if anything? What were the pilots reactions to any warning? etc., etc., etc.