Which of the following instrument approach procedures is NOT authorized?

The answer provided identifies RNAV (RNP) as the procedure that is not authorized, which needs clarification. In the context of instrument approach procedures, all options listed — ILS, RNAV (RNP), VOR, and GPS — are typically authorized under certain conditions, with each serving specific operational needs.

RNAV (RNP), or Area Navigation (Required Navigation Performance), is a type of RNAV that includes performance requirements for the navigation system. It is commonly used and can be authorized provided the aircraft and crew meet the necessary criteria. The use of RNP procedures allows aircraft to fly more precise paths and enables approaches at airports that may not have traditional approach options available, enhancing overall operational efficiency.

The other mentioned procedures — ILS (Instrument Landing System), VOR (VHF Omnidirectional Range), and GPS (Global Positioning System) — are also widely utilized and authorized under their respective conditions. Each of these methods plays a significant role in supporting safe landing operations, particularly in varied weather conditions where visibility may be compromised.

Understanding which procedures are authorized for use is crucial for operational safety and regulatory compliance, and it's essential that pilots are trained on all available procedures to ensure they can effectively utilize the appropriate one for any given situation.