Air carrier Captain reported confusion with the setup of the special engine-out approach at SKRG; as there is some ambiguity that may lead to the use of the wrong VOR frequency and misidentification of the critical DME point.

Narrative

The primary issue I identified was the setup of the special engine-out approach; specifically the use of two different VORs. While this might seem straightforward to some; it was not immediately clear to me during the preflight review a few days before my flight. This ambiguity poses a potential hazard; as pilots may inadvertently use the wrong VOR frequency and misidentify the critical 13 DME point; especially if the Flight Control Computer (FCC) switches sides or annunciators change unexpectedly.Detailed Observations: Engine-Out Navigation Setup: The Río Negro reference guide currently uses two different VOR frequencies. The special engine-out turn point could be misidentified. This setup increases the risk of confusion; particularly during high-stress or non-normal scenarios like engine-out operations. Threat is if you zoom in on the special engine-out procedure you may not notice the RNG VOR.I propose using KOXEV (13.4 DME from RNG VOR; altitude 7800 feet); a fix already established on the ILS Z Runway 01 missed approach; as the designated two engine-out turn point. This fix is consistent with the normal two-engine go-around procedure; reducing potential errors and simplifying the approach.Alternate Proposal: If using KOXEV is not feasible; I recommend creating a crossing radial off the MRN VOR. This would allow pilots to set up the backup frequency for MRN VOR and cross-check distances effectively.Risks with Current Setup: The use of two separate VOR frequencies in the sector increases the likelihood of errors. For instance; if a pilot inadvertently references the MRN VOR instead of RNG VOR; they could end up misidentifying the 13 DME ring and potentially flying dangerously close to terrain or directly into a box canyon unable to avoid terrain. This risk is exacerbated if the FCC or annunciator unexpectedly switches sides during the approach; leading to confusion about which radial or distance is being displayed. As with an engine fail; generator interruption would switch the FCC Master (MA) to the opposite side if it was on the side with the failed engine.