Which statement about altimeter settings is correct?

Which statement about altimeter settings is correct?

• A. QNH is a standard pressure setting of 29.92 inches of mercury.
• B. QNH yields height above the local airfield.
• C. QNH yields altitude above mean sea level.
• D. QNH is not used in flight.

Answer: (C)

The key idea is that the altimeter setting adjusts the instrument’s reference pressure so the reading corresponds to height above mean sea level. When you set local QNH, you’re calibrating the altimeter to the area’s sea‑level pressure, so the altitude shown is the aircraft’s height above mean sea level. The other statements don’t fit this concept: the standard pressure of 29.92 inches of mercury is the standard setting (QNE) used to read pressure altitude, not altitude above sea level; height above the airfield is what you’d get with QFE rather than QNH; and QNH is indeed used in flight to monitor altitude above mean sea level.

The key idea is that the altimeter setting adjusts the instrument’s reference pressure so the reading corresponds to height above mean sea level. When you set local QNH, you’re calibrating the altimeter to the area’s sea‑level pressure, so the altitude shown is the aircraft’s height above mean sea level.

The other statements don’t fit this concept: the standard pressure of 29.92 inches of mercury is the standard setting (QNE) used to read pressure altitude, not altitude above sea level; height above the airfield is what you’d get with QFE rather than QNH; and QNH is indeed used in flight to monitor altitude above mean sea level.