Emergency Descent Calculator

This calculator times an emergency descent — the kind flown after a rapid decompression, engine fire, or smoke in the cabin — and checks whether you can get down before hypoxia takes over. Descent time is simply the altitude to lose divided by your target vertical speed, and horizontal distance covered is derived from groundspeed times that same descent time, so a faster VSI shortens both the time aloft and the ground track consumed. True airspeed is estimated from indicated airspeed using the standard approximation that TAS runs about 2% higher than IAS per 1,000 feet, evaluated at the average of your start and target altitudes, then reduced by any headwind to get groundspeed.

The calculator also reports time of useful consciousness (TUC) — the rough window of useful cognitive function without supplemental oxygen — using widely-cited altitude bands (roughly 15–20 seconds above FL400, down to 30+ minutes below 15,000 ft), and flags whether your planned descent completes before that window closes. If a bank angle is entered it also computes turn radius for a turning descent, though the vertical-speed target itself is assumed constant through the turn rather than degrading with bank. Oxygen duration comes from a rough D-cylinder approximation (about 0.07 liters of gas per PSI) divided by your selected flow rate — treat both the TUC bands and this oxygen figure as planning approximations, not certified duration data, since actual TUC varies with individual physiology and activity level, and cylinder capacity varies by hardware.