search was cut short. just six hours into its mission the bluefin-21 surfaced. 14 hours early. the bluefin was originally expected to scour the ocean floor for debris. the whole journey lasting 20 hours. but instead, the device resurfaced after the o official say it exceeded the operating depth of 14800 feet. >> we just hit a deeper spot than we initially planned so we just got to bring it up, reprogram it, shift a little bit away from the deeper area. and adjust our search pattern. meanwhile, a new detail emerging. a u.s. official tells cnn the co-pilot's cellphone was on during the flight and made contact with the malaysian cell tower. according to information shared by malaysian investigators. that cellphone signal reportedly detected about 30 minutes after the plane made that sharp westward turn, around the time the aircraft disappeared from