What does "substitute means of navigation" refer to in RNAV usage?

The term "substitute means of navigation" in the context of RNAV (Area Navigation) usage specifically refers to utilizing a suitable RNAV system when traditional navigation instruments or methods, such as non-operable avionics, are not available. This allows pilots to maintain safe and effective navigation without relying on conventional navigation aids that may be temporarily out of service.

In practical terms, if a pilot finds themselves with inoperable equipment that would normally provide navigation support, employing an RNAV system can serve as a reliable alternative. This practice ensures that flights can continue safely and effectively without being hindered by equipment failures.

The other options do not accurately align with the definition of "substitute means of navigation." While conventional NAVAIDS and operational conventional NAVAIDS are mentioned, they do not reflect the concept of substituting an RNAV system for equipment that is not functioning properly. Additionally, using visual flight rules for navigation is a separate concept and does not relate directly to the use of RNAV systems.