AIRBUS A320-232JETBLUE AIRWAYS CORP

The airplane was descending through 12,500 feet on approach to the airport. The airplane was jolted as it flew through a small cumulus cloud. Specifically, the airplane dropped about 20 feet instantaneously, experiencing a positive g-load of 1.98, followed by a negative g-load of -0.43, less than 1 second later. During that time, a seated passenger did not have her seatbelt fastened. She fell forward into the stowed tray table in front of her, fracturing two ribs. A second passenger was in an aft lavatory and suffered two spinal fractures. The captain had made a passenger announcement during initial descent and prior to the turbulence encounter, emphasizing the need for passengers to take their seats and fasten their seatbelts when the seatbelt sign was illuminated. Additionally, a flight attendant made a public announcement when the seatbelt sign was illuminated. The seatbelt sign had been illuminated since 19,000 feet (about 4 minutes prior) and the airplane was not flying through any precipitation. The captain had also instructed the flight attendants via intercom to sit down a few minutes prior to the turbulence encounter.