Air Canada flight AC376 was parked at gate 127. The aircraft was cleared to push back. There was one person driving the tug, and one person monitoring the left wing. There was a catering truck parked 20 feet to the rear, starboard (right) side of the aircraft. The truck had completed servicing an aircraft at gate 129, and was waiting to service another aircraft at gate 125. The driver was in the cab of the truck completing paper work. As the aircraft was pushed back the person monitoring the left wing noticed the truck parked in the path of the aircraft being pushed back. He tried to signal to the tug driver, however, could not get his attention. The driver of the catering truck also noticed the approaching aircraft, and vacated the truck cab. The aircraft struck the catering truck, which toppled onto its side. The aircraft sustained substantial damage to the rudder and rear fuselage.