True or False: Sinus blocks most often occur during ascent.

The statement is false because sinus blocks can occur during both ascent and descent in aviation, although they are more frequently associated with the latter. Sinus blocks, often related to sinus barotrauma, happen when there is an imbalance between the pressure in the sinus cavity and the ambient atmospheric pressure. While rapid changes in altitude, such as during ascent, can contribute to sinus discomfort, the risk is generally higher during descent when the air pressure increases and the sinus cavities may not equalize properly. This can lead to blockage if the Eustachian tubes are unable to function effectively, which may be exacerbated in individuals with pre-existing sinus or respiratory conditions. Therefore, understanding the physiological changes during different phases of flight is crucial for recognizing when sinus blocks are more likely to occur.