When does a sinus block most frequently occur?

A sinus block most frequently occurs during descent due to the changes in ambient pressure that affect the body’s sinuses. During descent, as the aircraft decreases altitude, the pressure outside the body increases, while the pressure inside the sinuses may not equalize quickly enough. This can cause discomfort and blockage as the pressure differences build up. The rapid change in altitude demands a quick response from the body’s physiological systems to equalize pressure, and if there is any blockage or disturbance in the nasal passages or sinuses, this can lead to the condition known as a sinus block.

In contrast, conditions such as ascent, level flight, and takeoff generally do not produce similar pressure imbalances within the sinus cavities as prominently as descent, where the pressure differential is most pronounced.