Are dual accounts permitted in AirwaySim? Can two or more players use a single account (as long as they don't have another account)?
Each user is only allowed have a single account. But for two persons using one account .. I wouldn't recommend.
Anyway, looking at the usage terms, it is said that the account information is for your personal use only. But if the users are same family or live under the same roof, then it could be doable. And you are of course responsible of using the account so that you know what is happening there (= if the other user does something to your game while you are away, it's entirely your responsibility).
As Sami said, it's not allowed, however, I do believe that you can play with one account in different games if you so chose. The only thing is the payment for each game.
As I understand Sami, it's allowed, but not recommend, as I'm responsible for my account and to what my partner does.
However, I know I can trust him and it's easier to make decisions together, then alone.