ISA Deviation Calculator

Every pilot knows the moment: you need ISA deviation for a performance calculation, the freezing level for icing risk, or a cold-temperature altitude correction — and you're doing it by hand at 0300 local time. Stop doing ISA deviation math on the back of a nav log. Set the ISA deviation in your FMC the right way. In under 10 seconds. On any day of the year. WHY IT MATTERS The FMC assumes standard atmosphere unless told otherwise. On an ISA+20 day, that assumption puts your TOD kilometres off and your descent path several hundred feet from where idle thrust will actually hold it. A correct ISA deviation value fixes that. - Accurate TOD. Start descent where the aircraft actually wants to start, not where a ICAO standard day says it should. - Cleaner idle descent. Less speedbrake, less thrust on descent, less energy-management on the way down. - Stable non-precision approaches. FMCs that…