If cabin depressurization occurs at FL240, what vertical mode should be used?

In the event of cabin depressurization at Flight Level 240, the most appropriate vertical mode to use is descent. This is because a rapid altitude reduction is necessary to bring the aircraft down to a more breathable atmosphere, typically below 10,000 feet, where oxygen levels are sufficient for passenger and crew safety without supplemental oxygen.

Using a descent mode allows the aircraft to initiate a controlled and steady decrease in altitude, guiding it to a safe level quickly and effectively. In contrast, other modes such as climb, speed, or altitude hold may delay the necessary descent, exposing those onboard to hazardous conditions related to a loss of cabin pressure. Therefore, implementing a descent mode is critical for ensuring safety and responding appropriately to a depressurization event.