Definition
A specification for the oxygen used in aircraft breathing systems requiring at least 99.5% pure oxygen by volume, with no more than 0.005 milligrams of water per liter and minimal other contaminants. This grade is designated as 'Aviator's Breathing Oxygen' (ABO) and is the only oxygen approved for use in aircraft oxygen systems.
Plain English
A required quality level for the oxygen pilots breathe in flight. It must be very pure and very dry, so it works reliably at altitude and won't freeze or contaminate the system.
Context Anchor
Seen when studying aircraft oxygen systems, servicing oxygen bottles, or choosing the correct type of oxygen for flight.
Derivation
“Aviator” comes from a Latin word for bird and came to mean a person who flies. “Oxygen” comes from Greek roots originally meaning “acid-former,” an early mistaken idea about the gas. In this term, the important point is that “breathing oxygen” means oxygen prepared for people to breathe, and “aviator’s” narrows it to the stricter aviation use.
Why Pilots Care
Using oxygen that fails this standard can introduce moisture that freezes in lines or contaminants that cause illness or system failure at altitude.
Grounding Statement
At altitude, the oxygen system can get very cold, so even a small amount of water in the oxygen can freeze and interfere with oxygen flow.
Intuition Check
Do not assume “oxygen is oxygen.” For aviation, the standard is not only about how pure the oxygen is; it is also about how dry and safe it is for aircraft breathing systems.
Example Sentence 1
Before the high-altitude flight, the lineman confirmed the cylinder had been filled to the aviator's breathing oxygen purity standard.
Example Sentence 2
Before flight the crew checked that the oxygen supply complied with the Aviator's Breathing Oxygen Purity Standard to avoid line blockage.