Find Out Why Planes Fly AT 38000 feet

The main reasons are that there is less air resistance (drag) and the engines are typically more fuel efficient due to lower air temperature and air pressure. The next best reason is you are above most of the weather. Fun Fact: When your pilot announces that you are flying at 38,000 feet … you aren’t. You are flying at Flight Level 380. The change from feet the FL (Flight Level) units are at 18,000 feet, in the US and Canada. FL is measured in 100 feet increments so difference between FL190 and FL180 is 1,000 feet. Why FL? The height of an airplane is measured by barometric pressure on an Altimeter instrument.

Because the local pressure changes due to weather and other factors there is a knob to set the pressure. It’s call the Kollsman window where this is read / set.

As you go higher, the air is less dense and less affected by changes. Also it would be pain to set the altimeter every 10 minutes as you scoot across the sky in and out of different pressure area.

So above 18,000 ft (or the transition altitude) you just set the altimeter to 29.92, which is a standard setting. Everyone does that so everyone is reading the same.

Your altimeter may readout 38,000 but you might be at 37,500 or 39,200 feet. But since everyone is using the same standard setting, all the planes stay apart from each other.

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Credit: Dave Pompea

Private Pilot