During which phase are sinus and ear blocks most likely to occur?

Sinus and ear blocks are most likely to occur during descent due to the rapid change in atmospheric pressure. As an aircraft descends, the air pressure outside decreases, and if the Eustachian tubes (which connect the middle ear to the throat) are unable to equalize the pressure in the middle ear with the cabin pressure, it can lead to a blockage. This is because the increased pressure juxtaposed with a failure to equalize can cause discomfort and potentially pain, resulting in what is commonly known as "ear barotrauma."

Conversely, during ascent, although changes in pressure do occur, the Eustachian tubes usually can equalize the pressure more effectively since the body can adjust to the decrease in pressure more readily. In cruise, there is no significant pressure change that would lead to blockages, and during landing, the pressure change is more controlled and gradual, reducing the likelihood of similar issues arising. Hence, the dynamics of pressure change during descent place the body at a higher risk for experiencing these types of blockages.