A Cessna 501 Citation I/SP was destroyed when it impacted Lake Percy Priest shortly after takeoff from Smyrna Airport, Tennessee (MQY). The pilot and six passengers were fatally injured. The airplane departed at 10:53:06 and entered the clouds when making a climbing right turn to the east. The airplane then began to descend, and air traffic control (ATC) asked the pilot to confirm altitude and heading. The pilot did not respond. After a second query from ATC, the pilot acknowledged the instructions. The airplane entered a climbing right turn from 1800 feet to 3000 feet. After ATC made several attempts to contact the pilot, the airplane entered a rapid descending left turn and impacted a shallow reservoir at a high rate of speed. Weather at the time of the accident included a 1300 feet overcast. Probable Cause: The pilot’s loss of airplane control during climb due to spatial disorientation.