Definition
Air-filled cavities located in the frontal bone of the skull, just above the eyebrows and behind the forehead. Each sinus connects to the nasal passages through a small opening, allowing air pressure inside the sinus to equalize with outside air pressure during altitude changes.
Plain English
Hollow spaces in the bone above your eyebrows that are filled with air and connected to your nose through small drainage holes. They need to balance their air pressure with the cabin pressure as you climb or descend.
Context Anchor
Seen in aeromedical discussions about sinus problems, especially when flying with a cold, allergy, or sinus congestion.
Derivation
Frontal' comes from the Latin 'frons,' meaning forehead. 'Sinus' is Latin for 'cavity, hollow, or curve.' Together: the hollow spaces in the forehead. Knowing the location helps explain why pilots with sinus blockage often feel sharp pain in the forehead area during pressure changes.
Why Pilots Care
During pressure changes in flight the frontal sinuses must equalize through their narrow ducts; blockage produces sharp forehead pain that can distract or incapacitate a pilot.
Grounding Statement
If swelling blocks the small opening from the frontal sinus to the nose, the trapped air may not adjust as cabin pressure changes.
Intuition Check
Frontal does not mean the front of the airplane here; it means the forehead area of the skull. Sinuses are not just a stuffy nose; they are air spaces that can trap pressure.
Example Sentence 1
The pilot canceled the flight after a head cold blocked his frontal sinuses, knowing the descent would likely cause severe pain.
Example Sentence 2
The preflight briefing reminded students that a head cold could trap air in the frontal sinuses and cause pain at altitude.