Up in Air last night and these dropped off A Thunder Spirit on the first isle. In fact 4 of them dropped. Being the only SK up there got one and the rest went to some lucky SKs in other guilds.
The currently-named Plane of Sky was called the Plane of Air until the release of the Planes of Power expansion, which had its own Plane of Air (Eryslai, the Kingdom of Wind). To avoid confusion, the old Plane of Air was renamed to the Plane of Sky.
At the time the poster posted (Feb 2002), his terms were accurate (PoP was released in the fall of 2002).