The LOTRO Game Servers will be brought down on Wednesday, April 3rd from 7:00 – 10:00 AM Eastern (-5 GMT) for an update to the game. Thanks for your patience, and we’ll see you back in the game soon! Patch notes will be available during the downtime.
Source: LOTRO Forums
According to Cordovan on the forums, this update should make the “Flight to the Lonely Mountain” instance available once again: