The noninstrument-rated pilot obtained weather forecasts for a cross-country flight, which indicated visual flight rules (VFR) conditions with clear skies and visibilities that varied between 4 to 10 miles along his intended route. The pilot then departed on a dark night. According to a performance study of radar data, the airplane proceeded over land at 5,500 feet. About 34 miles west of Martha's Vineyard Airport, while crossing a 30-mile stretch of water to its destination, the airplane began a descent that varied between 400 to 800 feet per minute (fpm). About 7 miles from the approaching shore, the airplane began a right turn. The airplane stopped its descent at 2,200 feet, then climbed back to 2,600 feet and entered a left turn. While in the left turn, the airplane began another descent that reached about 900 fpm. While still in the descent, the airplane entered a right turn. During this turn, the airplane's rate of descent and airspeed increased. The airplane's rate of descent eventually exceeded 4,700 fpm, and the airplane struck the water in a nose-down attitude. Airports along the coast reported visibilities between 5 and 8 miles. Other pilots flying similar routes on the night of the accident reported no visual horizon while flying over the water because of haze. The pilot's estimated total flight experience was about 310 hours, of which 55 hours were at night. The pilot's estimated flight time in the accident airplane was about 36 hours, of which about 9.4 hours were at night. About 3 hours of that time was without a certified flight instructor (CFI) on board, and about 0.8 hour of that was flown at night and included a night landing. In the 15 months before the accident, the pilot had flown either to or from the destination area about 35 times. The pilot flew at least 17 of these flight legs without a CFI on board, of which 5 were at night. Within 100 days before the accident, the pilot had completed about 50 percent of a formal instrument training course. A Federal Aviation Administration Advisory Circular (AC) 61-27C, "Instrument Flying: Coping with Illusions in Flight," states that illusions or false impressions occur when information provided by sensory organs is misinterpreted or inadequate and that many illusions in flight could be caused by complex motions and certain visual scenes encountered under adverse weather conditions and at night. The AC also states that some illusions might lead to spatial disorientation or the inability to determine accurately the attitude or motion of the aircraft in relation to the earth's surface. The AC further states that spatial disorientation, as a result of continued VFR flight into adverse weather conditions, is regularly near the top of the cause/factor list in annual statistics on fatal aircraft accidents. According to AC 60-4A, "Pilot's Spatial Disorientation," tests conducted with qualified instrument pilots indicated that it can take as long as 35 seconds to establish full control by instruments after a loss of visual reference of the earth's surface. AC 60-4A further states that surface references and the natural horizon may become obscured even though visibility may be above VFR minimums and that an inability to perceive the natural horizon or surface references is common during flights over water, at night, in sparsely populated areas, and in low-visibility conditions. Examination of the airframe, systems, avionics, and engine did not reveal any evidence of a preimpact mechanical malfunction.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot's failure to maintain control of the airplane during a descent over water at night, which was a result of spatial disorientation. Factors in the accident were haze, and the dark night.
Full Narrative here: http://www.ntsb.gov/ntsb/brief2.asp?ev_id=20001212X19354&ntsbno=NYC99MA178&akey=1