At 1050 eastern time, a Cessna 414 was destroyed after the pilot declared an engine ice emergency during a circling approach to runway 23 at Greeneville-Greene County Municipal Airport. The pilot was a recent FAA Southern Region CFI of the Year. Three passengers were also killed, and a pilot-rated passenger was seriously injured. During radio communications with Tri Cities approach, the pilot reported that he had the AWOS report from Greeneville and the approach controller advised the pilot to expect some light icing from about 6,000 feet all the way down. The pilot was vectored to and cleared for the Localizer Rwy 5 approach.The pilot subsequently reported on the CTAF that he was planning to circle to land on runway 23. After the airplane passed the airport on downwind, two witnesses heard a garbled transmission on the Unicom frequency. The pilot stated, Emergency, engine, ice. The witnesses went outside and observed smoke north northeast of the airport. An off-airport witness saw the airplane flying northbound in straight and level flight between 200-250 feet agl when it made a sharp left turn, collided with trees and crashed.