I always hear two sides to the DME arc approach. One is that the DME arc approach must begin at the IAF (where the airway or radial meets the arc). Second is that the the entire arc itself is the IAF and you can essentially pick up the arc anywhere. Any thoughts or references on which is correct?

I don't have the books in front of me right now - but I think the technical answer is that the approach still starts at the IAF; but I have asked and been allowed to join the arc at another point besides the actual IAF before - in training.

I know APC - someone will soon post the exact right answer and with the reference and probably even a link here soon

USMCFLYR

I can't answer with a reference but as far as I know, you have to join at an IAF. Many arcs are there for a reason, i.e. terrain. Think if you just randomly joined an arc previous to the published point and ran in a big rock.

I could be wrong, though.

If you joined previous to the published arc, you're not on the approach. If you follow the min altitudes, you should be safe anywhere between the IAF and FAF. You could easily come in at or above the MSA and descend on a published portion of the approach if you had the distance to do so.

It's like most other approaches. Non-radar it must start at an IAF. But ATC can radar vector you to intercept at any point along the way
Here's the FAA Legal opinion that talks about the non-radar environment

http://www.faa.gov/about/office_org/...ARC%20IAFs.pdf

There isn't one that specifically talks about radar.

No, you cannot join (or you will not be cleared to join) on the arc outside an IAF unless there is a published transition there.

You can join the arc inside the IAF...only make sense,if you can join at the IAF and then fly over the arc at X altitude you should be able to join the arc at X altitude inside the IAF. Just make sure you have enough distance to make the turn to final and descend...those are the usual challenges.

You can be radar vectored to join but it will be inside the IAF. My previous job we were vectored to just outside the lead in radial all the time at our home airport.

Hadn't noticed that someone was talking about joining and arc where there was no arc ("outside" the IAF). No, you can't do that.