cannula

In aircraft cabins, a cannula is a flexible tube that carries supplemental oxygen from a pressurized source directly into the nostrils of a pilot or crew member. The tube typically branches into two small prongs, one inserted into each nostril, held in place by a loop that runs over the ears and under the chin. Modern aviation cannulas are made from medical-grade silicone or plastic; older versions used rubber compounds that degraded with exposure to altitude, temperature swings, and ozone.

Pilots use cannulas during unpressurized flight or in cabins where pressurization has failed. At high altitudes, ambient oxygen partial pressure drops dangerously; a cannula delivers oxygen at flow rates between 2 and 4 liters per minute, measured by a rotameter at the oxygen panel. The tube itself is rated for burst pressures well above cabin oxygen supply pressure, typically 50 to 100 pounds per square inch gauge. Connections are made via quick-disconnect fittings or threaded couplings that conform to military specifications such as MIL-DTL-6030.

Maintenance crews inspect cannulas for cracks, kinks, discoloration, and blockages before each flight. Silicone tubes degrade if stored in direct sunlight or near hydraulic fluid and solvents; they should be kept in opaque containers in a cool, dry environment. A cannula with a collapsed tube section, visible crack, or hardened plastic prongs must be removed from service immediately. Flow testing is performed by attaching the cannula to an oxygen supply and observing rotameter readings; insufficient flow suggests a kinked tube or obstructed prongs.

Variants and applications

Single-prong cannulas exist but are uncommon in aviation; the two-prong design ensures better oxygen distribution and more stable fit during rapid head movement in the cockpit. Some aircraft use nasal masks instead of cannulas for high-altitude flight, offering higher oxygen concentration and more reliable delivery when breathing hard during emergency descent. Portable oxygen systems for general aviation often pair a small cannula with a reusable bottle held in a lap bag; commercial airlines stock cannulas for passenger medical oxygen but keep them separate from the crew oxygen system.

The term comes from Latin cannula, meaning small reed or tube. Historically, pilots called them "breathing tubes" or "oxygen tubes," but medical terminology standardized the name. A cannula differs from a mask in that it does not seal against the face and allows carbon dioxide to mix with ambient air, limiting its use to flights where cabin altitude remains below roughly 10,000 feet equivalent. At higher altitudes, a pressure mask with a demand regulator becomes necessary to maintain consciousness.