What PSI is indicated by the vacuum gauge at the 15K mark?

The indicated PSI on the vacuum gauge at the 15K mark is 4.3 PSI. This value is derived from understanding the normal operating ranges and characteristics of the vacuum system equipped in the King Air 350. At altitudes around 15,000 feet, the vacuum system's performance can be influenced by atmospheric pressure and engine performance, which are calibrated to reflect an optimal and safe operating level for performance reliability.

The choice of 4.3 PSI represents a specific threshold that ensures adequate vacuum pressure for the proper functioning of instrumentation and systems that rely on vacuum suction, such as gyroscopic instruments. This is crucial for maintaining accurate readings and ensuring safe operation during flight, particularly at higher altitudes where reduced atmospheric pressure can impact engine performance and system efficacy. Maintaining the correct vacuum gauge reading at this altitude helps pilots confirm that the vacuum systems are operating within safe parameters, essential for effective aircraft control and navigation.