At App in the Air we don't have a standard definition of the account to log in and log out.
You can optionally use different login ways (Google / TripIt / any email via IMAP option) to import flights. You can use later on such ways of "login" to sync your flight data and subscription across devices (iOS / Android).
However, you can disconnect any account you connected. Just go to the app's settings and tap on it, then confirm.