At what altitude is the altimeter set to 29.92 inches of mercury?

The correct altitude at which the altimeter is set to 29.92 inches of mercury, also known as "standard pressure," is 18,000 feet MSL (Mean Sea Level). At this altitude, pilots transition from the use of local altimeter settings, which can vary due to local weather conditions, to a standardized altimeter setting. This is a crucial point for flight operations because above this altitude, all aircraft operating in the United States—under Instrument Flight Rules (IFR)—use a common reference pressure, simplifying navigation and ensuring vertical separation between aircraft.

The altimeter setting of 29.92 inches of mercury is used in the standard atmosphere model, which helps in maintaining consistent altitude reference among various aircraft flying at high altitudes. This policy establishes a common baseline, allowing pilots to avoid confusion that could arise from differing local altimeter settings. Thus, it creates a uniform operating environment for all aircraft above this critical altitude.