What action is required when entering Class A airspace to ensure standard pressure and separation?

• A. Maintain current altimeter
• B. Change altimeter to 29.92 so everyone is on a level playing field and separation can be achieved
• C. Increase power
• D. Reduce speed

Answer: (B)

Class A airspace uses flight levels that are based on a standard pressure reference. When you enter this airspace, you set your altimeter to 29.92 inches of mercury so everyone is reading from the same pressure surface. This standardization lets ATC maintain consistent vertical separation between aircraft, regardless of actual weather pressure at lower altitudes. If you kept the local altimeter setting, your reads could drift relative to others’ flight levels, making separation unreliable. Changing to 29.92 doesn’t change engine power or speed; it simply fixes the pressure reference used for altitude. That’s why updating the altimeter to 29.92 is required to ensure standard pressure and safe separation.