Definition
Outside air temperatures significantly colder than the standard atmosphere value at a given altitude, which cause a pressure altimeter to indicate an altitude higher than the aircraft's actual height above the ground. The colder the air, the more compressed it becomes for a given pressure, so the altimeter — which assumes standard temperature — overreads. This effect becomes operationally significant on instrument approaches in very cold conditions, where uncorrected indicated altitudes can place the aircraft dangerously close to terrain or obstacles.
Plain English
When the air is much colder than normal, your altimeter shows you higher than you actually are. On an instrument approach in very cold weather, that means you could be lower than the chart's altitude says, which can be dangerous near terrain.
Context Anchor
Seen in weather planning, inadvertent IMC risk assessment, icing discussions, and instrument approach procedures that require cold-temperature altitude corrections.
Why Pilots Care
Uncorrected cold temperatures can place the aircraft lower than indicated, raising the risk of controlled flight into terrain on approaches.
Grounding Statement
In cold, wet conditions, a pilot may be dealing with both ice risk and an altimeter that makes the aircraft appear higher than it truly is.
Intuition Check
Do not read cold temperatures as just a comfort issue. In aviation, cold temperatures can affect aircraft handling, icing risk, and the actual height of the aircraft above the ground.
Example Sentence 1
Because of the cold temperatures forecast at the destination, the crew applied the published altitude correction to each segment of the approach.
Example Sentence 2
In cold temperatures the crew flew the entire procedure at a higher indicated altitude to maintain the required terrain clearance.