The first thing a flight attendant notices about you isn't your appearance.

As you step onto the plane and are greeted by a flight attendant, you’re probably just thinking about finding your seat and getting your luggage stored away.

But that flight attendant saying hello? Well, they’re checking you out.

It’s not about appreciating your appearance, however. The cabin crew members are trained to notice things about you and make an assessment.

In a split second they decide whether you would be a help or hindrance should an emergency arise.

Experienced flight attendant Sjaak Schulteis tells The Sun the first thing on-air staff figure out is what language you speak, judging by what's in your hand.

"We pay attention to their language and check if they hold a magazine or newspaper," Schulteis says, adding that flight attendants might try to greet passengers in their native tongue.

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There's a safety aspect to that detail, though, fellow flight attendant Janice Bridger adds.

"If a person cannot understand English, they cannot understand shouted commands, nor can they read the instructions on how to open the exits," she explains.

"That may disqualify someone from sitting in the exit row."

Another detail flight attendants will notice straight away is if a passenger is drunk, which cabin crew member Gaea Peregrinor says can be cause for refusing your entry on the plane.

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Flight attendants will also pay close attention to your physical fitness. The person sitting in the exit row has to be fairly strong, Bridger explains.

"They need to be able to physically lift a heavy hatch (up to 27kg) or open a heavy door (more than 100kgs)," she tells The Sun.

Meanwhile, Peregrinor — who revealed this training in response to a question posed on Quora — says that if you're particularly strong, you might end up being called upon later.

"If I see someone who is muscular, powerful, strong, physically fit, I memorise his/her face and make a mental note of where they are sitting," she says.

"In the event of an attack on the flight or on me, these are my 'go-to' people. If a situation looks like it could develop, I’ll privately and discreetly ask one of these people if they would be willing to help us if necessary."

This might involve restraining an unruly passenger, or any heavy lifting.