Before you would have to quest in the Sholazar Basin to get the ability to fly in Northrend. That’s apparently changed as there is now a flight trainer over at Krasus’ Landing in Dalaran. Images courtesy of WOR.
Cold Weather Flying (required to use flying mounts in Northrend) is now trainable in Dalaran for 950gold.

Also the new debuff in Dalaran restricting players from using flying mounts has been activated.

Gimme some of that gold. No, seriously, I’m 72 and trying to get to Dalaran. By the time you read this I’ll be dead.