Upvote:3
No as a citizen of the united states (or anyone holding valid U.S. visa) you do not require a transit visa. This is only where you do not need to leave the airport and pass through immigration (eg transferring between different airports) or where you would have a second schengen layover - again requiring you to enter the schengen zone - even if you remain airside the whole time. schengenvisainfo
European Commision Visa policy - second source