And are there health risks associated with it?

Because the main engines aren’t on yet, the APU functions to keep passengers comfortableduring boarding.

“The initial start-up of the APU could/will often have a lingering burnt petroleum smell,” he says.

Passengers on board an airplane

Passengers inside the cabin of a commercial airplane during flight.Credit:enviromantic/Getty Images

Maaz adds that pressurized air from the APU helps start the main engines.

But what exactly is burning to cause the odor?

Welch says it’s typically superheated air passing through the aircraft’s air system.

“Some of the exhaust smell burning jet fuel makes it into the cabin,” adds Maaz.

And is there cause for concern?

A spokesperson from theEnvironmental Defense Funddirected me to an article showing that consistentlong-term exposurecan pose health risks.

However, Maaz says there’s no reason to worry because a typical passenger’s exposure time is limited.

Welch advises that you should only be alarmed if you see smoke.