A Part 121 turbine-powered airplane is cruising at FL390. Under 14 CFR 121.578, what is the maximum permissible cabin ozone concentration for any 3-hour average period?
- A0.25 ppm by volume.
- B0.20 ppm by volume.
- C0.30 ppm by volume.
- D0.15 ppm by volume.
Show answer & explanationAnswer & explanation
Correct answer: D. 0.15 ppm by volume.
14 CFR 121.578(d)(1) states that no person may operate a turbine-powered airplane at or above FL180 with passengers aboard unless the concentration of ozone in the cabin is no more than 0.25 parts per million by volume at any time above FL320, and no more than 0.1 parts per million by volume, time-weighted average for any 3-hour segment above FL270. The question asks for the 3-hour average, which is 0.1 ppm. Note that 0.1 ppm is equivalent to 0.10 ppm.
Why the other options are wrong
- A. 0.25 ppm is the maximum allowed at any time above FL320, not the 3-hour average.
- B. This value is higher than the regulatory limit for the 3-hour average.
- C. This value is higher than any regulatory limit for cabin ozone concentration.
Cabin Ozone Concentration (121.578)
14 CFR 121.578 regulates cabin ozone concentration in turbine-powered airplanes. Above FL270, the 3-hour average must not exceed 0.1 parts per million (ppm) by volume. Above FL320, the concentration must not exceed 0.25 ppm at any time.
- Applies to turbine-powered airplanes with passengers above FL180.
- Maximum 0.1 ppm (3-hour average) above FL270.
- Maximum 0.25 ppm (at any time) above FL320.
Memory trick: Ozone's a hazard, 3 hours at point one, at any time, point two-five's done.