The Main Maintenance Bay is a location in Xenoblade Chronicles. It is located on the ground floor of Galahad Fortress. There is an Earth Ether Gear here, as well as a lift to a lower floor (requiring the Fortress Pass Key to activate). There are three rooms joining the bay - the 1st Fuel Supply Room, 2nd Fuel Supply Room and 3rd Fuel Supply Room.
It is most likely a place for damaged Mechon to be repaired in the fortress.