Why should you set the altimeter to 29.92 when operating in Class A airspace?

• A. To maintain same pressure altitude across airspace
• B. To save fuel
• C. To improve engine performance
• D. To avoid turbulence

Answer: (A)

In Class A airspace, traffic is separated by flight levels, which are based on a standard pressure reference. Setting the altimeter to 29.92 inches of mercury makes your instrument read pressure altitude rather than true altitude. This standard reference means all aircraft at a given flight level share the same vertical reference, regardless of current sea‑level pressure, ensuring consistent separation across the airspace. If you used a local setting, readings could differ between aircraft due to weather-driven pressure changes, compromising ATC separation. The other options don’t address how vertical separation is achieved in this airspace.