Once tasked to investigate a suspected double TRU failure above FL 410. Airborne, enter 45 deg steep turn and spiral up to FL410. Each TRU off in turn - no problems. Then idle, full airbrake and a 60 deg steep descending spiral back down to earth - initial, break for a visual circuit to roll than back out for a PAR to land. Total flight time 40 minutes. Ac? Vulcan.