She is going to get off at the airport in America.

She is going to get to the airport in America.

She is going to meet some of her friends in America.

She is going to fly in the airplane.

She is going to get off on the trap in the airplane.

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I have written down some English expressions. Would you check the expressions and correct ungrammatical expressions. Am I using correct prepositions?

The second and last of those sentence are not correct usage.

Sure! Let's go through each sentence and address any grammatical errors or incorrect prepositions.

1. She is going to get off at the airport in America.
- This sentence is grammatically correct and uses the correct preposition "at" to indicate the location of getting off, which is the airport.

2. She is going to get to the airport in America.
- This sentence is grammatically correct and uses the correct preposition "to" to indicate the direction or destination of reaching the airport.

3. She is going to meet some of her friends in America.
- This sentence is grammatically correct and uses the correct preposition "in" to indicate the location where she will meet her friends, which is America.

4. She is going to fly in the airplane.
- This sentence is grammatically correct and uses the correct preposition "in" to indicate the means of transportation, which is the airplane.

5. She is going to get off on the trap in the airplane.
- This sentence is ungrammatical. The correct phrase would be "She is going to get off the plane." or "She is going to disembark from the plane." The word "trap" is not commonly used in this context. Additionally, we don't use the preposition "on" when referring to getting off a plane.

In summary, the first four sentences are grammatically correct and use the correct prepositions. The fifth sentence contains a grammatical error and an uncommon or incorrect word choice.