Definition
A device installed in some aircraft that allows the pilot or crew to urinate during flight. It consists of a funnel connected by a flexible hose to a vent line that discharges the fluid overboard through a drain tube on the aircraft's underside.
Plain English
An in-flight urinal. A funnel and hose that lets the pilot pee during a long flight, with the waste vented outside the aircraft.
Context Anchor
Seen in descriptions of older aircraft equipment, military aircraft, long-flight aircraft, and cabin or equipment checks.
Derivation
From 'relief' meaning easing of a bodily need, plus 'tube' for the hose that carries the fluid overboard. The name is straightforward and descriptive.
Why Pilots Care
Enables safe, uninterrupted flight on long missions by removing the need to leave the controls or land prematurely.
Intuition Check
Do not read relief tube as a pressure-relief tube or a ventilation tube. Here, relief means allowing a person to relieve themselves during flight.
Example Sentence 1
Before departing on the eight-hour ferry flight, the pilot checked that the relief tube was clear and the overboard drain was unobstructed.
Example Sentence 2
Before the ferry flight, the crew checked that the relief tube was clear and properly vented.