Incident
At 1407:11, the flight was cleared from Flight Level 240 to descend and maintain FL190. At 1409:08, the controller cleared the flight to descend and maintain 15,000 feet, and the pilot read back the clearance at 1409:17. At 1410:20, the controller instructed the pilot to expedite descent through 16,000 feet for traffic, but there was no response. From 1410:33 to 1417:21, the controller made ten attempts to contact the pilot without response. At 1417:26, the controller requested the pilot to ident if he could still hear him; at 1417:38, an ident was received, and the controller instructed the pilot to descend and maintain 15,000 feet. At 1418:36, the controller cleared the aircraft for the GPS approach and requested an ident acknowledgment, but there was no response. The aircraft impacted a rocky drainage trench near the base of a rock outcropping on a magnetic heading of 200 degrees in a wings-level, approximately 40-degree nose-down attitude, 15 nautical miles east-southeast of the destination airport at an elevation of 5,630 feet mean sea level.
Investigation Findings
Examination of the aircraft's flight control, pressurization, and electrical systems revealed no anomalies that would have precluded normal operations. Thermal damage to the aircraft showed no evidence of an inflight fire. Both engines underwent a complete teardown examination, revealing no evidence of catastrophic or pre-accident failure; both engines were functioning at the time of impact. Radar data indicated the aircraft was in level flight at FL190 for over four minutes, despite being cleared to 15,000 feet. It subsequently climbed to 20,300 feet before beginning a right descending turn followed by a left descending turn. The last radar return before loss of contact showed the aircraft at 15,900 feet and descending. No evidence of icing greater than light rime icing was present, and weather was unlikely to have been a factor.
Pilot Medical History
The pilot was taking two medications for high blood pressure and one for high cholesterol. Recent findings indicated elevated blood sugar, suggesting early diabetes or other systemic disease or injury. The pilot had a family history of heart disease and high blood pressure and had experienced at least one episode of chest tightness in the past. It is possible that he had unrecognized heart disease. The circumstances suggest substantial impairment or incapacitation of the pilot. Possible causes include a stroke or heart attack related to his medical conditions, or hypoxia from a decompression event without supplemental oxygen. However, there is insufficient information to conclude a specific cause for the pilot's impairment or incapacitation.