Those moments just before take-off can create a lot of anxiety. The lights flicker; the air turns on and off; the plane makes all kinds of weird mechanical noises and you are not sure what they are.

But you really don’t need to worry, it’s all part of the process.
According to Gizmodo, these noises are all part of a checklist of operations that happen before a plane can take off.
First, you may have noticed a dull hum whenever you walk on a plane. This is actually the plane’s auxiliary power unit, which keeps its systems up and running while the main engine is off.

In fact, most planes are hooked to the ground electricity and air systems to save gas. Which is good, because gas is especially more important while you’re in the air.

When you see the plane doors close, lights tend to flicker and air flow changes — but this is merely because they’re changing from the auxiliary to the plane’s main system for the flight.

It is like when you first power up a computer or laptop; you will notice a noise as the discs and fans starting to spin, then it quiets down as you get ready to work.

According to the Aviation Safety Network, 2017 was the safest year in flying. So even if you get a little nervous when you hear a noise before take-off, remember that your flight might just be the safest part of your day.