"I get on an airplane at the airport."
For long-term verbs (most verbs), we use で. We use に for short-term verbs like "to be, to stay, to live, to wait". I hope It was helpful.
で is the way something is done. How are we boading the plane? Via the airport, so its airportで. The action is "getting on". Where are we doing that? On the plane, so its Airplaneに. It quite a nuanced example
で marks the method (the airport), and に marks the destination (the airplane).
Basically for the verb のります you always use the particle に to indicate the vehicle you're boarding or in which you already are, and in japanese sentences in general you want to avoid using the same particle even if it acts in different ways, therefore here you use で to indicate the place where the action is taking place.
I reversed the position of ひこうきに and くうこうで and DL marked this wrong. The correct particles were connected to the appropriate nouns and the verb was correct and in the correct position. Basically I wrote "At the airport, I get on an airplane." I thought that was all right to reposition nouns and their particles. Is this an error? Please advise. Arigato in advance.