https://itunes.apple.com/nz/app/air-...304851207?mt=8
"Can't board with Watch app
by thebrockoli
Unfortunately boarding passes in the Watch app don't work, as the screen automatically turns off when you rotate the Watch upside down to scan at the gate. As a workaround, boarding passes stored in Passbook on Watch work fine - Apple is able to keep the screen on in that app, no matter how you're waving your arm about. Otherwise, the design of the Watch app is fantastic!"