The airplane was substantially damaged at about 0035 Eastern time during a collision with trees during maneuvering flight. The non-Instrument-rated Private pilot and passenger were fatally injured; night visual conditions prevailed. The flight departed Long Island MacArthur Airport (ISP) in Islip, N.Y., with the Fulton County Airport in Johnstown, N.Y., as the planned destination.The pilot was in radio and radar contact with the Albany Terminal Radar Approach Control (TRACON) and receiving flight following services. About 0034, both radio and radar contact was lost; the TRACON did not receive a distress call from the pilot. At about 0030, three witnesses reported an airplane descended through a cloud layer with an increase in engine noise. The noise was continuous, with no sputtering. Two of the witnesses reported that the airplane was initially on a northwesterly heading, and then made a left turn toward a southeasterly direction, before descending rapidly into terrain. A nearby weather reporting stations observation close to the time of the accident included visibility of 10 miles, scattered clouds at 2100 feet, a broken ceiling at 2600 feet and an overcast ceiling at 3400 feet.