Cabin ozone concentration

This regulation limits ozone concentration inside the passenger cabin on flights at high altitudes, where atmospheric ozone is more prevalent and can cause health issues for passengers and crew.

Airlines operating above Flight Level 270 (27,000 feet) must demonstrate that cabin ozone won't exceed 0.1 parts per million (time-weighted average) on flight segments over 4 hours. Above Flight Level 320 (32,000 feet), the limit is 0.25 parts per million at any time. These limits are measured at "sea level equivalent" conditions.

Airlines prove compliance through statistical analysis of ozone at their operating altitudes or by showing their ventilation/ozone control systems keep levels below these limits. The FAA may grant temporary exemptions if compliance creates unreasonable economic burden and the airline has a plan to achieve compliance.

The regulation doesn't apply to flights carrying only crew and certain authorized personnel, or to aircraft scheduled for retirement or re-engining under specific circumstances.

*This is a plain-English summary for study only. The official 14 CFR text on this page is controlling — always read the current regulation and consult a CFI.*