What is the primary altitude reference when using the VNAV system?

The primary altitude reference when using the VNAV (Vertical Navigation) system in the King Air 350 is barometric altimeters. Barometric altimeters measure altitude based on atmospheric pressure, which decreases as altitude increases. This system is used for altitude awareness during flight, ensuring that the aircraft operates within safe altitude limits and adheres to airspace restrictions.

The VNAV system relies heavily on barometric input to determine the aircraft's vertical profile and to execute descent or ascent instructions according to the air traffic control clearance or flight plan. It provides a reliable means of navigation especially in conditions where GPS accuracy may fluctuate.

In contrast, while GPS altitude readings can provide useful information, they are not the primary reference utilized for altitude in VNAV systems, particularly because GPS data can be less reliable in certain atmospheric conditions. Radar altitudes are typically used for checking terrain clearance close to the ground rather than for standard flight navigation throughout various phases of flight. Standard temperature corrected altitudes are utilized more for performance calculations rather than for primary altitude references in navigation systems.