I see on some approaches the words "Procedure N/A from V-123 Westbound". My guess is that there is some magical number of degrees of a turn that, if exceeded, would make a particular approach undoable. But if you were cleared direct to the fix where this notation would be located and you were not exactly on the Victor Airway specified, could you still fly the approach? What is the "magic" that applies this term to some approaches? See the following as examples:
RNAV (GPS) RWY 13 KASX
RNAV (GPS) RWY 27 KARR
Yet, if I were flying Eastbound to Northbrook (OBK) VOR on the 269 degree radial and intending to fly the VOR RWY 26 into 3CK, apparently I could turn more than 180 degrees to get back onto the inbound course of 269 degrees to fly this approach as there is no note telling me the the Procedure is N/A when arriving at OBK on the 269 degree radial.
I would appreciate it if anyone has a definate answer to this question and can support their response with references that I can eventually quote when asked this question again.