Why cold temperature matters to an altitude indication
An altitude number deserves context. Temperature is one of the reasons an indicated barometric altitude can differ from the aircraft’s true altitude. This is a conceptual introduction, with a look at the planning workspace in coolAltitude.
Indicated altitude is not always true altitude
In air colder than standard, true altitude is lower than indicated barometric altitude. The FAA AIM explains this effect and the applicable cold temperature airport procedures. Whether and how a correction is required depends on the procedure and operating rules; use the current authoritative source for your flight.
Review the inputs together
In the coolAltitude workspace, review your airport and approach entries, altitude levels and temperature. Keep their units and reference points visible. The approach profile brings these entries into one view alongside distances and descent information, which can help you spot an input that does not match the intended scenario.
Use the profile to support preparation
Compare the displayed levels with the current chart and your independently verified planning data. Return to saved approach entries only after checking that they still match the scenario you are reviewing. The value of a saved setup is convenience; its contents still need checking.
Keep altitude corrections and deicing separate
coolAltitude also includes deicing information, timers, holdover table notes and FAA references. Those tools address a different question from an altitude profile. Review the source edition and limitations for the tool you are using; a timer or displayed range does not establish that an aircraft is safe to depart.
Common questions
Is this a calculator for an operational correction?
No. This article explains the concept and illustrates the app. Use current approved procedures, documentation and your applicable operating rules for operational decisions.
Why show an approach as a profile?
A profile lets you review related levels and distances together during preparation and compare them with the information you entered.
Official reference: FAA AIM · Cold Temperature Barometric Altimeter Errors