What are the differences between ILS and RNAV approaches and what determines minima?

• A. ILS uses satellite navigation with vertical guidance; RNAV uses ground-based guidance.
• B. ILS uses localizer/glideslope with ground-based guidance; RNAV uses satellite navigation with vertical guidance; minima depend on equipment and approach type.
• C. ILS and RNAV approach minima are identical across all airports.
• D. ILS is only used for precision approaches when GPS is unavailable.

Answer: (B)

The main idea is that instrument approaches differ in how guidance is provided and this directly affects published minima. ILS is a precision approach that relies on ground-based equipment: a localizer for lateral guidance and a glideslope for vertical guidance, both transmitted from stations near the runway. RNAV approaches use satellite navigation (GNSS) and onboard navigation to determine position; some RNAV procedures include vertical guidance (APV, like LPV), while others provide only lateral guidance (LNAV) with a published altitude constraint. Minima are the weather and height/visibility thresholds necessary to continue to a safe landing, and they depend on both the type of approach and the available equipment. ILS minima are defined by decision altitude/height tied to the precision nature of the approach, and RNAV approaches with vertical guidance have their own DA values, while RNAV LNAV has an MDA. Because obstacle clearance, runway environment, and the level of guidance vary by approach type and equipment, minima are not identical across all airports or procedures. So the correct idea is that minima depend on the combination of equipment and approach type.