When is the first indication of slow decompression likely to occur?

The first indication of slow decompression typically occurs around 14,000 feet. At this altitude, the difference in pressure between the inside of the aircraft cabin and the outside atmosphere becomes significant enough to start impacting the physiological state of the passengers and crew.

Above this altitude, individuals may begin to experience symptoms related to hypoxia, which is a deficiency in the amount of oxygen reaching the tissues. Recognizing this threshold is crucial for crew members, as it underscores the importance of maintaining proper cabin pressure to ensure the safety and comfort of everyone on board.

Lower altitudes, such as 10,000 feet or 8,000 feet, generally allow for easier acclimatization by passengers, often resulting in minimal or no visible symptoms of hypoxia. Meanwhile, the threshold at 16,000 feet represents an altitude where physiological effects become more pronounced for individuals not acclimated or using supplemental oxygen but still occurs after indications can start being felt at 14,000 feet. Hence, 14,000 feet is the most critical point for recognizing the onset of issues related to slow decompression.