There are certain letters that may spell bad news if you spot them on your boarding pass.
One travel expert explained what the letters SSSS mean when printed on the boarding passes of hopeful holidaymakers.
Taking to social media to share the warning, the expert explained the four S's stand for "Secondary Security Screening Selection" and mean that you could face some additional airport security checks before jetting off.
The video, shared on TikTok, revealed that the letters mean officials will likely give you a pat down in order to check for any security breaches.
Additionally, the extra checks include swabbing for explosive residue as well as opening up all of you bags to perform a thorough check.
Travel expert Michelle explained in a video: “This is something you never want to see on your boarding pass: The quadruple S.
"It means you’re going to get searched super thoroughly, and it’s usually found on international flights to the US.
The majority of passengers with the SSSS on their boarding passes are picked at random.
However, those with the code on their pass are likely to be monitored by the US Department of Homeland Security.
Michelle explained how to clear up the problem, saying: “If you go to the US Department of Homeland Security website, you can apply for a redress number which prompts the DHS to review your record and clear up any erroneous or weird info that could be triggering the additional security measures.
“Once they’ve investigated your records and you’re hopefully cleared, you’ll want to input your redress number on all of your flight reservations going forward, and you should hopefully be good to go.”
There are a number of other tell-tale codes that can be found on your boarding pass.
For example, the two letters at the beginning of the flight number will relate to the airline you are flying with.
These codes are issued by the International Air Transport Association (IATA) - the trade body for international airlines.
Codes include BA for British Airways, VS for Virgin Atlantic and QF for Qantas - all airlines have a unique code
The numbers following these codes reveal a lot more information.
The general rule is the lower the number the more renowned - and often more longer distanced - the route. QF1 is for a Qantas flight from London to Sydney.
Pilot Patrick Smith previously told news.com.au: “Airlines often give lower numbers to their more prestigious, long-distance routes,
“If there’s a flight 001 in an airline’s timetables, it’s the stuff of London-Sydney or Paris-New York.”
It is also worth noting whether your flight number is odd or even. Those with even numbers are flights heading east or north with odd number heading in a south or west direction - there are some exceptions to this one.
Weirdly, some flight numbers are influenced by superstition. The number eight is considered lucky in many Asian cultures so is therefore likely to be included in most Asian routes.
United Airlines’ flight from San Francisco to Beijing is UA888.
Rarely seen numbers include 13, 666 and even 911.
The flight routes involved in the 9/11 attacks have been renumbered.
Numbers of crashed flights are also often retired. The Kuala Lumpur to Beijing route formerly flown by Malaysia Airlines flight MH370 now uses the number MH360.
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