PLT042: Constant Pressure and Isotach Charts
What code PLT042 covers, why the FAA tests it, and how to study Constant Pressure and Isotach Charts before your checkride.
Interpret Constant Pressure charts / Isotachs Chart
What this means for your checkride
A constant pressure analysis chart shows conditions on a surface of constant pressure aloft (for example 500 millibars), plotting the height of that surface, temperature, and winds. Isotachs are lines of equal wind speed drawn on such a chart, used to locate jet streams and areas of strong wind aloft.
Upper-air charts drive route and altitude planning and turbulence avoidance, so the FAA tests reading heights, temperatures, winds, and isotachs on a constant pressure chart.
A constant pressure chart is not a map of surface pressure; it shows the height of a pressure surface, so a low height corresponds to low pressure aloft.
Where to study it
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.