What should the altimeter be set to when climbing through 18,000'?

When climbing through 18,000 feet, the altimeter should be set to 29.92 inches of mercury (inHg). This is the standard pressure setting that is used above 18,000 feet in the United States and many other countries. The transition altitude, which is typically at 18,000 feet, marks the point where pilots switch from using local altimeter settings to standard pressure settings. Setting the altimeter to 29.92 ensures consistency in altitude readings amongst aircraft operating at higher altitudes, which is crucial for maintaining safe vertical separation between aircraft.

Using any other setting, such as 30.01, 29.50, or 30.15, would result in altitude discrepancies, which could lead to conflicts in air traffic. Therefore, it is important for pilots to understand and apply the rule of setting the altimeter to 29.92 in order to ensure safe and efficient operations in controlled airspace above the transition altitude.