What is the acceptable altimeter setting range when in controlled airspace?

The acceptable altimeter setting range when in controlled airspace is specifically designed to ensure that aircraft maintain appropriate vertical separation from one another and adhere to the air traffic control requirements. The range of 29.92 to 30.20 inches of mercury is established because it represents a standard pressure setting and a slight variance that can accommodate changes in weather conditions while maintaining safety and reliable altitude readings.

The standard altimeter setting of 29.92 inches of mercury is used as the basis for the transition altitude, typically set at 18,000 feet in the U.S. Above this altitude, pilots are required to use this standard pressure setting to ensure a consistent and uniform reference from which to measure altitude. The slight increase to 30.20 inches allows for local variations in pressure that may occur due to weather systems, ensuring pilots can appropriately adjust their altimeters based on the current atmospheric conditions while still adhering to safety protocols.

This range helps manage and maintain the safety of all aircraft operating under air traffic control (ATC), minimizing the risk of altitude conflicts while navigating through shared airspace.