Background
The flight was on an Instrument Landing System (ILS) approach to Runway 32. The air traffic controller provided information on cloud tops and in-cloud icing. The pilot acknowledged and inquired about the status of the locator, and the controller reported that all ILS components, including the outer marker locator, were monitoring normal.
Accident Sequence
At four miles from the outer marker or final approach fix (FAF), the pilot received a final vector, clearance for the ILS approach, and clearance to circle and land on Runway 23. The pilot acknowledged the transmission. Subsequently, radio and radar contact with the aircraft was lost.
The aircraft crashed approximately two miles southeast of the FAF. At the time of impact, the aircraft was in a steep descent on a heading of 140 degrees. No preimpact part failure or malfunction of the aircraft was found, although the aircraft was extensively damaged.
Investigation
Approximately three weeks after a boating accident on July 2, 1988, the pilot was admitted to a hospital and treated for a stroke. However, an autopsy and toxicological tests did not reveal any condition that would have prevented the pilot from performing his duties.
The investigation noted that Airworthiness Directive (AD) 88-13-01, which concerns aircraft equipped with M-4C/D autopilots, was not complied with. All four occupants were killed.
Probable Cause
The official probable cause was determined to be the failure of the pilot to maintain control of the aircraft, due to spatial disorientation, at about the time he was changing radio frequencies during an IFR approach. Findings include weather conditions of clouds, icing conditions, and low ceiling.