The ILS / LOC approach at KCXY states radar is required. I understand I can't fly the approach if not in radar contact. However, if flying the LOC approach I think I can identify both final and HORVI (for lower minimums) using HAR VOR. There's no reason I'd need the controller to call out a fix. If that is true, why is radar required? I think it would be more of a safety concern because of terrain and an adjacent airport (HAR Int)?
Radar is most likely required in this case because there is no defined Initial Approach Fix (IAF). This means that ATC needs to give vectors to final or otherwise provide a specific clearance to establish an IFR aircraft on the approach.
There may be other considerations, but that is the main one that I see here.
As mentioned above, this approach has no IAF.
That's because the the VOR is at 1,301 MSL (note the height of the obstacle next to the VOR is 1,410), and the segment from TIVNE to HORVI descends from 2,800 to 1,340 MSL, and will dip below the usable volume of a Low Altitude VOR. According to AIM 1-1-8, a low altitude VOR with a standard service volume cannot be received inside 10 miles and below 1,000 feet above the NAVAID.
Radar is required because there are no "published non-radar transitions" for this approach. Since most (almost all) instrument approach procedures are designed to allow a non-radar transition from the enroute phase of flight to the approach phase, any instrument approach that does not have published transitions requires "Radar."
Also, if there is a mandatory stepdown fix on the approach that cannot be identified by any other means (GPS/DME/VOR), the approach stipulates "Radar Required" (ref: FAA Oder 8260.19f)
From the FAA's hand book on IFR flying (page 4-17). It seems that it is the minimum equipment required to fly the approach.
In some cases, other types of navigation systems, including radar, are required to execute other portions of the approach or to navigate to the IAF (for example, an NDB procedure turn to an ILS, or an NDB in the missed approach, or radar required to join the procedure or identify a fix). When ATC radar or other equipment is required for procedure entry from the en route environment, a note is charted in the plan view of the approach procedure chart (for example, RADAR REQUIRED or AUTOMATIC DIRECTION FINDER (ADF) REQUIRED). When radar or other equipment is required on portions of the procedure outside the final approach segment, including the missed approach, a note is charted in the notes box of the pilot briefing portion of the approach chart (for example, RADAR REQUIRED or DISTANCE MEASURING EQUIPMENT (DME) REQUIRED). Notes are not charted when VOR is required outside the final approach segment. Pilots should ensure that the aircraft is equipped with the required NAVAIDs to execute the approach, including the missed approach. Refer to the AIM paragraph 5-4-5 for additional options with regards to equipment requirements for IAPs.
Later on they talk about Radar Approaches (Page 4-71)
The two types of radar approaches available to pilots when operating in the NAS are precision approach radar (PAR) and airport surveillance radar (ASR). Radar approaches may be given to any aircraft at the pilot’s request. ATC may also offer radar approach options to aircraft in distress regardless of the weather conditions or as necessary to expedite traffic. Despite the control exercised by ATC in a radar approach environment, it remains the pilot’s responsibility to ensure the approach and landing minimums listed for the approach are appropriate for the existing weather conditions considering personal approach criteria certification and company OpSpecs.
They can also be useful in helping disabled aircraft in (page 4-74).
Perhaps the greatest benefit of either type of radar approach is the ability to use radar to execute a no gyro approach. Assuming standard rate turns, ATC can indicate when to begin and end turns. If available, pilots should make use of this approach when the heading indicator has failed and partial panel instrument flying is required.