What happened to Claus in Last Exile? Near the end of Last Exile: Fam, the Silver Wing, we see our former protagonist Claus...


   ...in a wheelchair.


Is there any official explanation as to why?  He's never featured in Fam the Silver Wing, so we don't know how this happened from that series alone.
Last Exile: Fam, the Silver Wing - Aerial Log, documents Claus in the time between Travelers from the Hourglass, and Fam, the Silver Wing. Claus sustained serious injuries in a one on one confrontation with an amnesiac Dio, when the latter arrived on Earth tracing his faint memories. While his resulting injuries have confined him to a wheelchair, Claus has forgiven the recovered, and deeply remorseful Dio. Claus' confident promise to heal and find his way back to the skies has comforted Dio. In return, this allowed Dio to find a renewed purpose to make sure the skies will be there to welcome Claus back