bellmouth

The pumps were about 9 1/2 feet above the suction bellmouth, which was about 10 inches above the bottom of the tank and about 22 inches starboard of the sump's centerline. Because the bellmouth was offset to the starboard side of the sump's centerline, the system was more susceptible to losing suction from a port list. Thus, the NTSB concludes that the port list, coupled with the vessel’s motion, most likely caused air to enter the bellmouth of the suction pipe to the lube oil service pump, which resulted in a loss of oil pressure that caused the main engine to shut down.