The pilot had anticipated some turbulence along the route of flight, briefed his three passengers, and turned on the seat belt sign. At flight level (FL) 240, the flight encountered turbulence, and the pilot requested clearance to deviate from air traffic control (ATC), which ATC provided. Using on-board weather radar, the pilot determined that he needed a greater deviation and made several urgent requests for a clearance to deviate. ATC was not able to approve the deviation but instructed the pilot to descend from FL 240 to FL 200. During the descent, the airplane encountered the first of four 15- to 20-second severe turbulence events, with a 5- to 10-second interval between events. During the events, the pilot made several urgent requests for a deviation, but ATC was not able to approve the requests. As far as the pilot was aware, all the passengers were in their seats with seat restraints on during the turbulent portion of the flight. One of the passengers was an elderly man, and one passenger was his caregiver. The caregiver reported that she had gotten out of her seat to assist the elderly man in adjusting his restraints more firmly. During the time she had gotten up to assist, she was thrown about the cabin during the turbulence. The pilot landed the airplane as soon as possible, and the caregiver was treated at a local hospital for bone fractures to her right arm. Probable Cause: The passenger’s decision to unbuckle her restraints during an in-flight turbulence event, resulting in serious injury.