I'd just completed the transit check and was driving back to the office when over the radio I heard the aircraft reg being mentioned, so returned, to find a set of canopied steps had reversed of the aft pax door and proceeded to reverse to a position on the other side, awaiting an inbound aircraft on the next stand. In doing so managed to remove a triangular corner piece of the RH stabilizer T/E tip, 10 inches x 10 inches, which had plumeted to the ground. Long down time for the manufacturer to make the parts.