Indicated Altitude

Indicated altitude is the altitude displayed on the aircraft's altimeter when it is set to the current local altimeter setting (QNH or local barometric pressure). It represents the aircraft's height above mean sea level as measured by atmospheric pressure.

Indicated altitude is subject to errors from non-standard temperature and pressure conditions:

• Pressure error: If the actual pressure differs from the altimeter setting, the indicated altitude will be incorrect. The mnemonic "high to low, look out below" reminds pilots that flying from high pressure to low pressure without updating the altimeter setting results in the aircraft being lower than indicated
• Temperature error: In colder-than-standard temperatures, the aircraft is lower than indicated. This is particularly significant for obstacle clearance on instrument approaches in cold weather, and some operators apply cold temperature altitude corrections

Above the transition altitude, all aircraft set their altimeters to the standard pressure setting (29.92 inHg / 1013.25 hPa) and fly pressure altitudes expressed as flight levels, ensuring consistent vertical separation regardless of local pressure variations.