Fumblub Gearwind is a hostile level 71 rare mechanical gnome with approximately 14k health. He can be found flying his flying machine around the Geyser Fields in the Borean Tundra and is one of three rare spawns in the zone. The other two are Old Crystalbark and Icehorn.
I have indicated the area he patrols in red on the map below. This npc is part of the Northern Exposure and Frostbitten achievements. He drops Fumblub's Seat Cushion which is a level 70 bind on equip leather chest item with a random enchant. Like other Northrend rares, he also drops Abandoned Adventurer's Satchel, which generally contains about 20 gold, a full stack of frostweave cloth, and often times a few crystallized elements.
Fumblub can be found patrolling in both clockwise and counter-clockwise directions and he hovers several yards above the ground. He will need to be hit with some sort of ranged attack to be pulled.
On a side note, his corpse can be salvaged by engineers, and the trinket Gnomish Universal Remote can be used to control him.