QNH

Set QNH and the altimeter reads altitude, so terrain and obstacle clearances mean what they say. It is passed with the clearance and in the ATIS, in hectopascals over most of the world and in inches of mercury in North America. Above the transition altitude everyone switches to the standard 1013.25 hPa instead, and reads flight levels.

Nearby in Aviation

• NOTAM — A notice telling crews about a temporary hazard or change — a closed runway, unserviceable lighting, an airspace restriction.
• pushback — Moving an aircraft backwards off its stand with a tug, because airliners cannot reverse under their own power.
• registration — The unique alphanumeric identity painted on an airframe, allocated by its country of registry.
• retro livery — A historic paint scheme reapplied to a current aircraft, usually for an anniversary.