If the altimeter is set to QNH, what does it indicate?

If the altimeter is set to QNH, what does it indicate?

• A. An altitude above mean sea level
• B. A height above airport elevation
• C. An altitude above regional pressure setting
• D. Flight level

Answer: (A)

Setting the altimeter to QNH makes it indicate height above mean sea level. QNH is the local mean sea-level pressure adjusted for the elevation of the observation point, so when you set it, the instrument is calibrated to read altitude relative to sea level. On the ground at the aerodrome, that reading roughly equals the airport's elevation above sea level; in flight, it shows your height above mean sea level. If you wanted height above the airport itself, you’d use QFE instead. When you see flight levels, that uses a standard pressure setting (QNE) of 1013 hPa, not QNH.

Setting the altimeter to QNH makes it indicate height above mean sea level. QNH is the local mean sea-level pressure adjusted for the elevation of the observation point, so when you set it, the instrument is calibrated to read altitude relative to sea level. On the ground at the aerodrome, that reading roughly equals the airport's elevation above sea level; in flight, it shows your height above mean sea level. If you wanted height above the airport itself, you’d use QFE instead. When you see flight levels, that uses a standard pressure setting (QNE) of 1013 hPa, not QNH.