During cold temperature operations, what correction function must not be used?

In cold temperature operations, the correct action is not to use the FMS Cold Temp Correction Function. This is crucial because the FMS Cold Temp Correction is designed to adjust performance calculations for warmer temperatures, but in cold conditions, the validity of that data diminishes. Using this correction can lead to inaccuracies in performance calculations, including takeoff and landing distances, which could adversely affect aircraft safety.

Additionally, in cold conditions, the aircraft may perform differently than indicated, and relying on the FMS Cold Temp Correction could give pilots a false sense of security regarding performance capability. This is particularly important during crucial phases of flight where precise calculations are essential for safety and efficiency.

The other functions mentioned, which pertain to temperature deviation, altitude adjustment, and pressure altitude, serve their purposes in helping pilots manage their operations under varying circumstances and do not have the same risks associated with them in cold temperature scenarios.