Accident Sequence
While conducting an IFR arrival, the pilot received vectors for an ILS runway 16L approach. The aircraft was at an assigned heading of 270 degrees and altitude of 3,000 feet, approximately 8 miles north of the final approach fix. The controller then instructed the pilot to turn left to 185 degrees and descend to 2,200 feet until established on the localizer, followed by clearance for the approach. The pilot acknowledged these instructions. Approximately one minute later, communication and radar contact with the aircraft were lost.
Witness Observations
Eyewitnesses near the accident site observed the aircraft descending below the cloud layer. They described the airplane in a steep left bank with the nose down, and reported hearing the engines revving. Within seconds of visual sighting, the aircraft crashed. No fire or smoke was seen emanating from the airplane before impact.
Aircraft Examination
Post-accident examination of the airframe revealed no mechanical problems. The pilot did not report any difficulties with the airplane to the tower controller prior to the loss of contact.
Pilot Toxicology
Toxicology tests detected 0.323 mcg/ml chlorpheniramine (a sedating antihistamine) in liver fluid and 0.073 mcg/ml in kidney fluid. Additionally, unspecified levels of dextromethorphan (cough suppressant), pseudoephedrine (decongestant), and phenylpropanolamine (decongestant) were found in kidney and liver fluids. All these medications are available in over-the-counter cold remedies.
Probable Cause
According to the official findings, the probable cause of the accident was the pilot's failure to maintain control of the aircraft due to spatial disorientation. A related factor was the instrument weather conditions.