Accident Sequence
The aircraft was in level flight at 2,000 feet in instrument meteorological conditions when the pilot transmitted, "we've just lost our ahh artificial horizon." Approximately five minutes later, air traffic control lost radar contact and communications with the aircraft. A witness located about one mile north of the accident site reported hearing engine noise emanating from the water, describing the sound as loud and constant. The noise persisted for about 30 seconds and was followed by an "explosive collision/impact sound." The witness walked to the shore to locate the source but could not see anything due to fog.
Wreckage and Examination
The aircraft was found submerged in approximately 25 feet of water, with wreckage scattered over a 150- to 200-foot area. Recovered components included both engines, parts of the left wing, empennage, fuselage, seats, and interior. The attitude indicator was not recovered. A faint needle impression on the vertical speed indicator face indicated a descent rate between minus 2,500 and 3,000 feet per minute. Examination of the left and right vacuum pumps revealed no malfunctions or failures.
Probable Cause
The official probable cause was the pilot's failure to maintain control of the airplane after an undetermined failure of the airplane's attitude indicator. A contributing factor was fog.