An aircraft fume event is an incident in which smoke, fumes, a haze or an unusual smell enters the cabin or cockpit. On many airliners, the air you breathe in flight starts as bleed air: compressed air drawn from the engines. Most of the time it is clean. A 2002 National Research Council report explained that problems can arise when engine oil, hydraulic fluid or deicing fluid gets into that air supply by mistake. Here is how cabin air works, where contamination can come from, and what is and is not known.
How cabin air works
Jet engines compress outside air. Some of that compressed air, called bleed air, is drawn off and sent through the aircraft's environmental control system, where it is cooled and conditioned before it reaches the cabin. Fans also pull cabin air through filters and mix it back in. Outflow valves let air leave the plane and control cabin pressure. (National Research Council, Environmental Control)
Engines and the APU
Besides the main engines, most airliners have an auxiliary power unit (APU), a small turbine in the tail. It supplies electric power and compressed air, often while the plane is on the ground. The National Research Council noted that air from the APU is unfiltered. (National Research Council)
How contamination can happen
According to the report, problems arise when engine lubricating oil, hydraulic fluid or deicing fluid unintentionally enters the cabin through the bleed-air supply. When these fluids are heated to the high temperatures in the bleed-air system, laboratory studies suggest many compounds can be released. (National Research Council, Summary)
Other possible sources include electrical problems, spilled fuel and fumes from outside the aircraft on the ground. A smell on board is not automatically dangerous, and many odors have harmless causes.
How fume events are identified
People notice fume events by smell, by a haze or smoke, or by irritation. But a smell alone cannot identify a chemical. The National Research Council found that no exposure data were available to identify what was in cabin air during these incidents. Identifying the source of a specific event usually takes the aircraft's maintenance records and crew reports.
What federal rules say
- Airliner design rules require cabin and cockpit air to be free of harmful or hazardous levels of gases or vapors. (14 CFR 25.831)
- Part 121 airlines must report when an aircraft part causes smoke, vapor, or toxic or noxious fumes in the cockpit or cabin during flight. (14 CFR 121.703)
If you were on a flight with fumes
Save your boarding pass, flight number, date and seat, plus any photos, videos, texts and notes. Write down your symptoms and see a health professional if you have concerns. Our aircraft fume exposure page explains what to save and how claims may work.
This article is general information, not legal or medical advice, and reading it does not create an attorney-client relationship. Research on cabin air is ongoing, and this article does not claim that any illness was caused by aircraft fumes.
This article is general information about how these cases work. It is not legal advice, it does not create an attorney-client relationship, and no two claims are alike. If something here sounds like your situation, the useful next step is a conversation about the facts.