What secret 'Squawk 7500' code means and why you'd never want to hear it on a plane

There are a number of codes you don't want to hear on a plane, and overhearing 'Squawk 7500' is certainly not a good thing.

Aircraft staff have all sorts of secret codes so they can discuss things and let each other know what's going on in case there's an emergency or a matter that requires attention and the last thing they need is panicking passengers.

Flight attendants will even have secret codewords they use to tell each other if they like a passenger or not so they know and you don't, but 'Squawk 7500' is an altogether more serious secret signal.

According to travel experts at Wander it's one of the most serious things you can hear on board a plane and that's because it's an alert that the aircraft is facing a security threat such as being hijacked.

Squawk 7500 is the signal a transponder code sends when cabin crew want to send a warning so authorities on the ground know what's going on in the skies.

You don't want to be hearing Squawk 7500 while in the air (Kevin Carter/Getty Images)

"If you ever hear this code mentioned by the flight crew or air traffic control, it signals a potential security threat on the flight," they said.

While it can mean the plane is being hijacked it also generally means that something criminally bad is happening on board and that air traffic control or the police need to do something.

You do not want to be on board a plane that's got a Squawk 7500 going on.

There are many other codes you can hear on board a plane which typically mean some kind of warning.

There are several other codes you're better off not hearing (Getty Stock Photo)

Code 300 - Angel

If you hear the words 'Code 300' - or even 'Angel', it usually means there has been a tragedy on board.

Sadly, it means someone has died and cabin crew are now working to respond to the situation, from where to put the body to providing support to loved ones who might have been travelling with the deceased.

Code Yellow

If you're hearing 'Code Yellow' during your flight it means there is a minor medical problem on the plane, and staff will respond accordingly, such as providing a sick bag.

Pan Pan

Jumping up the health scale from a minor issue to one that is serious but not threatening, 'Pan Pan' alerts crew that someone is in more medical danger but is not expected to die.

Code Adam

This is one you never want to hear in an airport as it means there's a child missing somewhere in the vicinity, which obviously is massively distressing for the parents.

Mermaid

This one is informal slang among flight attendants and if you hear them say it you'll easily be able to see what they mean with a quick look.

A 'Mermaid' is a nickname for a passenger who sprawls themselves across several seats to stop others from sitting near them.

You're only likely to hear this on flights with few enough people on them that people can basically pick and choose where they sit as though they're on a bus.