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This glossary is written for virtual airline and flight simulation use within Virtual Air Canada Airline. It is not intended as a real-world aviation reference.
QNH is the altimeter setting that causes a standard pressure altimeter to indicate the aircraft’s altitude above mean sea level (MSL) when the aircraft is on the ground at a known elevation. It is the most widely used altimeter setting in aviation below the transition altitude. When set to the current local QNH, the altimeter reads the aerodrome elevation on the ground and provides altitude above MSL throughout the climb. QNH is derived from the actual atmospheric pressure measured at the station and corrected to mean sea level using temperature and elevation adjustments. QNH is broadcast on ATIS and reported by ATC in hPa (hectopascals) or inHg (inches of mercury) depending on the region. Below the transition altitude (typically 5,000 ft or 6,000 ft in Canada, 3,000-5,000 ft in parts of Europe), all aircraft use local QNH to ensure uniform altitude reference and terrain clearance. Above the transition level, all aircraft switch to the standard pressure setting of 1013.25 hPa (29.92 inHg), which changes the reference to Flight Level. The transition altitude and transition level form the transition layer where both settings may be in use simultaneously on climbing and descending aircraft.

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In Virtual Airline Operations

At Virtual Air Canada Airline, setting the correct QNH is a mandatory step in pre-departure and approach preparation. QNH is obtained from ATIS or the VATSIM controller and must be set on both altimeters before take-off and on descent through the transition level. Failing to set QNH on approach can result in incorrect altitude awareness and unstabilized approach conditions.
  • QFE - Atmospheric Pressure at Aerodrome Elevation
  • OAT - Outside Air Temperature
  • NOTAM - Notice to Air Missions