Three entrances at the airport

[Rachel Adams]

If my sentences are correct and my comments next to them too what should I use at the end of the fifth sentence "at" or "in"?

1. "I am at the airport." I am waiting for my flight. A general location.

2. "I am in the airport." In a specific place.

3. "I am going to meet her at the airport." Somewhere at the airport.

4. "I am going to meet her in the airport." In a specific place.

5. "There are three entrances at the airport." Or "in".

[Rover_KE]

. "There are three entrances at the airport." Or "in".

5. There are three entrances to the airport.

[GoesStation]

If my sentences are correct, and my comments next to them, too, what should I use at the end of the fifth sentence, "at" or "in"?

See above. Here's a more succinct way to say the same thing: If my sentences and comments are correct, what should I use at the end of the fifth sentence, "at" or "in"?

[teechar]

1. "I am at the airport." I am waiting for my flight. A general location.
2. "I am in the airport." In a specific place.

"In the airport" means inside the actual building.
"At the airport" can mean: inside the building, in the airport car park, on the tarmac waiting for takeoff or landing, etc.

[Rachel Adams]

"In the airport" means inside the actual building.
"At the airport" can mean: inside the building, in the airport car park, on the tarmac waiting for takeoff or landing, etc.

So a native speaker would not use "in the airport" if he is waiting for their flight but only "at".

[tedmc]

You can say you either wait in/at the airport.

[teechar]

So a native speaker would not use "in the airport" if he/she is waiting for their flight but only "at".

No. In fact, they are more likely to use "in" than "at" if they're waiting for their flight. See Piscean's post (and my previous post) above.
However, you might hear "I'm at the departure gate, waiting for my flight" because it's impossible to be in a gate!

[Rachel Adams]

We are more like to use 'in' with more restricted areas such as the departure lounge or the restaurant.

Then in my sentence if I am saying that there is a café in the airport, I should use "in" because it's a specific location not "at": 1. "There is a café in the airport."

But

2. "I am in a café at the airport". The specific location is "café" not the airport in the second sentence.

[teechar]

I don't understand why you insist on "specific". It's not about that. Forget about the airport for now. Which are you more likely to say: "I'm in a cafe downtown" or "I'm at a cafe downtown"? If you'd read Piscean's post above, you would have seen that the keyword there is "restricted".

[Rachel Adams]

I don't understand why you insist on "specific". It's not about that. Forget about the airport for now. Which are you more likely to say: "I'm in a cafe downtown" or "I'm at a cafe downtown"? If you'd read Piscean's post above, you would have seen that the keyword there is "restricted".

I used "specific" instead of "restricted", in my post, but I was expressing the same idea, I guess. I would use "in" in the sentence you are asking about because it's a restricted location.
But if I am mentioning two places what should I use?
"There is a café in the airport." "In" if I am talking about a restricted place and "at" if I am talking about"airport" in a general sense. Then I should remove the second "in" before "airport" and use "at".

If there is only one restricted place in the second sentence then I should use "in" before "café" and "at" before "airport".

2. "I am in a café at the airport". The "restricted" location is "café" not the airport in the second sentence.