What is the maximum ozone concentration, on a time-weighted average during any 3 hour interval, that is permitted above flight level 270?

The maximum ozone concentration allowed above flight level 270 is 0.25 parts per million (ppm) on a time-weighted average during any 3-hour interval. This limitation is established based on the need to ensure the safety and comfort of passengers and crew, as exposure to higher ozone levels can have adverse health effects and impair aircraft operation.

The specified threshold reflects regulatory standards for ozone exposure at high altitudes, where environmental conditions contribute to increased ozone formation. By maintaining the concentration at or below this level, the aviation industry aims to mitigate the risks associated with ozone while allowing for safe and efficient operation of aircraft in the upper flight levels. This standard is crucial for maintaining clear guidelines for flight planning and ensuring compliance with safety regulations.