If you fly a lot you might have noticed a strange looking detail on all of the main doors of the plane. There is a bright red strap going diagonally across the tiny window in the door. You might have also noticed that when the plane is stationary and the door is open this strap is moved away, leaving the window unobstructed. Why? What is its function?

This red strap is used in Boeing 737 and many other planes. It is usually attached to the window as soon as the plane starts moving towards the runway and is put away as soon as it reaches its final destination. People have guessed before that this strap might be some sort of handle or even have something to do with structural integrity of that little window. However, it is just a sign.

At the bottom of the door there is a large box with a slide mechanism inside. This slide is automatically inflated in the case of emergency and allows people to evacuate quickly and safely. However, this slide can be quite dangerous itself, because it inflates very quickly and violently. Basically, imagine an airbag, but much bigger and much more powerful. That red strap tells fire brigade that the slide is on.

Red strap on the door of Boeing 737 – when the slide is not armed, the strap is moved away from the window. (Vasyatka1, Artem Katranzhi, Wikimedia)

Rescuers can get inside of the plane from the outside, but they have to know if the slide is armed. They will adjust their strategy according to this information. Slide is actually always armed as soon as the plane leaves towards the runway. So why this strap is not left there permanently? Fire brigade professionals know that the plane has been moving, so they must know that the side is on.

In case of emergency the slide might be disarmed from the inside. For example, if plane has to land on its belly and the door gets damaged, flight crew may disable the slide so that fire brigade can open the door safely. But in most cases the strap does stay on from the moment the plane starts moving until it stops at the airport of destination.

This information was revealed in the video in Mentour Pilot’s YouTube channel. Here you can see the video:

Mentour Pilot’s creator also debunked an old Hollywood myth – main doors of the airline plane cannot be opened mid-flight. They are held in position by the pressure inside of the cabin – no locks are needed. So you cannot just throw out bad guys from the plane that easily.


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