About 20 years ago we took our Old English Sheep Dog (125lbs) on summer vacation with us. He was in a large cage, although not as big as the one you describe. It was a 10hr flight in a DC-10. He was sedated. The problem was leg two of the trip (a 45 min flight in a DC-9). The cage was too big for the cargo hold, so we colapsed it and the captain allowed me to take the dog into the cabin and use the last row of seats.