Time of Useful Consciousness of 15-20 seconds occurs at which flight level?

• A. FL300
• B. FL350
• C. FL400
• D. FL250

Answer: (C)

Time of Useful Consciousness is the brief window after a sudden loss of cabin pressure during which you can still think and act before you lose consciousness, because the brain has to keep getting enough oxygen and altitude reduces the amount of oxygen available. As you climb, the air’s oxygen content becomes harder to deliver to the brain, so that window shrinks. At around 40,000 feet, this window is typically about 15–20 seconds, which is why the given duration matches that altitude. In other words, a scenario reporting a 15–20 second TUC corresponds to flight level four hundred. At lower altitudes the TUC would be longer, and at higher altitudes it would be shorter, reinforcing why rapid donning of oxygen and descent are critical at this level.