On February 12, 1984, Jose Domingo Colmenares Vivas and his wife, Dilia Arreaza de Colmenares (plaintiffs) arrived at a Puerto Rico international airport. They got on an escalator within the airport. Mrs. Colmenares was standing in front of her husband and holding the hand rail. Suddenly, the hand rail portion stopped moving, while the stairs themselves kept advancing. Mrs. Colmenares lost her balance, and Mr. Colmenares grabbed her to prevent her from falling. In doing so, Mr. Colmenares lost his balance and tumbled down the escalator, suffering injuries. They brought suit against the Sun Alliance Insurance Co. (Alliance) (defendant), the liability insurer of the airport. Sun Alliance brought a third-party contractual action against Westinghouse Electric Corporation (Westinghouse), the maintenance company tasked with maintaining and repairing the escalator. At trial, airport staff testified about their routine maintenance procedures and contract with Westinghouse for inspections, maintenance, and repairs. Based on this testimony, the trial court concluded that there was no evidence the airport had been negligent. Additionally, the trial court declined to impose liability based on res ipsa loquitur because there was no evidence that the “injury-causing instrumentality,” the escalator, was at all times within the exclusive control of the airport.