An air pocket is a sudden drop caused by a change in the air. Hit an air pocket, an air pocket over the mountains.
There is no pocket and no hole, since what happens is the air moving downwards rather than being absent. The phrase survives because it describes the feeling exactly.
1nounair pocketA sudden drop caused by a change in the air.
“An air pocket put every drink on the ceiling.”
air pocket is a movement.
Practised in Airport & Flying