PLT173: Atmospheric Stability
What code PLT173 covers, why the FAA tests it, and how to study Atmospheric Stability before your checkride.
Recall atmospheric conditions - measurements / pressure / stability
What this means for your checkride
This covers how the atmosphere is measured and how stable it is: pressure and temperature with height, the standard atmosphere, and whether lifted air keeps rising (unstable) or sinks back (stable). Stability decides the cloud type, turbulence, and visibility you will meet.
Atmospheric stability sits underneath most of the weather a pilot flies through, so the FAA tests whether you can read pressure and stability indicators and predict the conditions they produce.
Candidates often reverse it: stable air gives stratiform clouds, steady precipitation, and poorer visibility, while unstable air gives cumuliform clouds, showers, turbulence, and good visibility between the buildups.
Where to study it
Practice questions on this code
Real questions from the Aviator IQ bank that test this exact area. Answer each to see the correct choice, the full rationale, and the FAA source.
What best characterizes an unstable atmosphere?
Oral checkride defense
A code on your report is an area the examiner can revisit. Here is how an examiner might probe it, and how to explain it out loud.
How does atmospheric stability change the weather you'll fly through?
Stable air resists vertical motion, giving stratiform clouds, steady precipitation, smooth air, and often poorer visibility. Unstable air gives cumuliform clouds, showers, turbulence, and good visibility between the buildups. Tie it back to the temperature lapse rate that drives whether lifted air keeps rising.
You expect an unstable air mass today. What do you brief the passengers?
Warn of a bumpy ride from convective turbulence, building cumulus, and possible showers, with good visibility otherwise. Plan timing to avoid the strongest afternoon heating when the instability and any thunderstorms peak.
A code on your test report is an area of deficiency. An authorized instructor must review it with you and endorse that review before you take the practical test, and the examiner may revisit it during the oral. Study it until you can explain it out loud, not just recognize the answer.