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April 18, 2017

To be human in the 21st century is to use marvelous new technology without ever really questioning how it works.

But last week, Chrissy Teigen tweeted that she doesn’t “like charging my phone on the plane because a large part of me feels like I am sucking energy and power from the engine.”

Two aerospace engineers leaped to the rescue in the comments, telling Teigen that she need not worry about draining the plane’s juice and causing everything to go haywire. And although Teigen most likely meant it as a joke, her tweet highlights a common misconception about how electricity onboard an airplane works.

Each engine onboard an aircraft — generally, commercial aircraft have two — is attached to a generator. These generators provide the electricity to power the equipment inside the aircraft, from cabin to galley to passenger seats. (The electrical system onboard most commercial aircraft is an alternating current [AC] system that typically supplies the plane with 115 volts of electricity at 400 hertz.)

In case of generator failure, all aircraft also include “auxiliary power units,” generally hidden inside the tail of the plane. And even beyond that, many aircraft are also equipped with “ram air turbines” to provide power in case of an emergency.

Passengers charging their devices needn’t worry about draining power that could be used for necessary electronic equipment in the cockpit. Generally, less than 1 percent of the power generated by the engines goes to the electric system onboard an aircraft.

And in fact, airplanes only need the energy produced from one engine to operate. At any given time when both of the plane’s engines are running normally, there are an extra 120 kilowatts of spare energy capacity. That’s enough to send 300 watts of electricity to 400 seats on the aircraft — and a phone charger uses about two to six watts while charging.

So next time Teigen has important business to take care of while on an airplane, she can safely plug in without worrying about draining the plane’s engine.

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