When you’re on a plane and the flight is just ready to begin, you’ll see and hear a few things:
- the flight attendants close the doors of the plane
- the aircraft starts to push back from the terminal
- you’ll hear one of the flight attendants say “Cabin crew arm doors and cross check.”
What Does It Mean When a Door Is Armed?
After that last one, flight attendants who are stationed at the emergency exits throughout the cabin will then activate the emergency slide by pushing a lever on the door. The door is now armed. That means if it’s opened, the emergency slide will deploy and inflate (if that happens, it happens really fast and looks like this).
Why Is There Red Tape on Some Plane Doors?
If you happen to be on a Boeing 737, and a few other types of planes, the cabin crew may also position a strip of red or orange tape diagonally across the window above the emergency slide. It’ll look something like this:
L: Red strap on the door of a Boeing 737. R: When the slide isn’t armed, the strap is moved away from the window. PC: Artem Katranzhi, Wikimedia, cc-by-sa-2.0
The box you can see on the bottom of the door on the photo above is the emergency slide.
How Emergency Personnel Know If a Door Is Armed
If there’s an emergency, the tape across the window signals to anyone approaching the aircraft from outside—such as a firefighter or any other emergency worker—that the door is still armed. If they try to open an armed door, the slide will automatically deploy (which could injure emergency personnel in the process). So the tape tells emergency workers to attempt to enter the plane from a different entrance.
If flight attendants are able to disarm the door, they do so and move the tape back to its original position above the door.
More Modern Aircraft Have a Better System
Every aircraft has some method of warning those outside when a door is armed. However, more modern aircraft have improved upon the 737’s warning system. On Boeing 757s, 767s, and 777s, as well as MD-11s, E-Jets, and all Airbus planes, if emergency workers try to open the door externally, the system will automatically push the arm handle to the disarmed position before opening.
However, if you’re on a 737, airlines still use the red tape technique.
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