On April 12, 2007, at 1315 Pacific daylight time, a Boeing 757-200, N525UA, experienced moderate turbulence while on descent into Los Angeles International Airport, Los Angeles, California. United Airlines operated the airplane under the provisions of 14 CFR Part 121. The 2 airline transport pilots and the 104 passengers were not injured; 1 flight attendant was seriously injured; and 5 flight attendants had minor injuries. The airplane was not damaged. Visual meteorological conditions prevailed, and an instrument flight plan had been filed. The flight originated at John F. Kennedy Airport, New York, New York, at 1151 eastern daylight time. United Airlines stated in the Pilot-Operator Aircraft Accident Report that while at flight level 400 (40,000 feet), the flight deck received information about turbulence below 12,000 feet. The captain advised the flight attendants to have the cabin secured and be in their seats within 15 minutes. The first officer gave the 'prepare for landing' announcement around flight level 250 (25,000 feet) as the airplane was descending, which was after the captain had notified the flight attendants to prepare the cabin, but before the end of the stated 15 minutes. While descending through 15, 500 feet, the airplane experienced a moderate 'jolt' lasting 1-2 seconds. By this time it had been more than 15 minutes since the captain gave the flight attendants the secure cabin instructions. The cabin crew reported injuries to all flight attendants and no injuries to passengers. All six flight attendants received medical attention after landing. One flight attendant was seriously injured with a closed fibular fracture; the five other flight attendants had minor injuries. In a written statement, the first officer said that turbulence departing New York had been very bad, therefore, in order to mitigate any passenger anxiety, when he made the 'prepare for landing' announcement he added that the turbulence would not be as bad as it was on departure. He understood the captain's instructions to the flight attendants, and this announcement was aimed at the passengers. In written statements provided by the flight attendants, they confirmed that they understood the instructions to have the cabin cleaned up and be seated within 15 minutes. As they were finishing the cabin clean up, the first officer's 'prepare for landing' announcement indicated that the turbulence would not be as bad as they expected. After landing, the airplane's Digital Flight Data Recorder (DFDR) was removed from the airplane. The DFDR data provided by United was examined by National Transportation Safety Board technical experts. The turbulence occurred as the aircraft was coming out of a 12-degree right bank and descending through 15,400 pressure altitude. The event lasted approximately 10-11 seconds, starting at Subframe Reference Number 43371 (20:28:18 GMT per the captain's clock, and 20:27:36 GMT per the GPS clock). The bank angle of the aircraft was between 8 and 1 degrees right wing down during the event. Vertical acceleration fluctuated between .5 and 2.06 G's. Longitudinal acceleration spiked up to .2 G's about the same time as the 2 G vertical spike. Lateral acceleration fluctuated between .1 G left and .05 G's to the right during the incident. The data showed that the autopilot was engaged and in control of the aircraft during the incident.