Cessna 150L N1539Q accident near Silverton, Colorado

Probable cause

The pilot's failure to maintain control of the airplane while operating it at low levels above mountainous terrain and in excess of its maximum allowable gross weight, which resulted in an aerodynamic stall. The pilot's failure to maintain control resulted from an acute cardiac event and incapacitation, hypoxia, or the effects of sedating medications or a combination of these factors. Contributing to the accident was the pilot's improper decision to takeoff above gross weight and without oxygen for the flight in mountainous terrain.

NTSB analysis

A witness saw the airplane flying low over mountainous terrain. He then saw the nose of airplane pull up, followed by the airplane flying inverted and departing controlled flight; the airplane's observed behavior is indicative of an aerodynamic stall. The airplane impacted rocky terrain at 12,570 feet mean sea level. The airplane was operating in excess of its maximum allowable gross weight. Further, the pilot was not using supplemental oxygen, despite a risk for hypoxia above 10,000 feet. The postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

The pilot's autopsy indicated moderate to severe diffuse coronary artery disease. This elevated his risk for acute coronary syndrome or an acute arrhythmia followed by incapacitation but would have left no evidence at autopsy. Further, hypoxia would have increased the likelihood of an acute cardiac event. Additionally, the pilot had significant levels of multiple impairing medications at the time of the crash that would have affected his ability to operate the airplane. The pilot was very likely impaired by this combination of sedating medications, even at levels that were probably therapeutic. Further, the medications would have affected his decision-making ability, which may have played a role in his decision to fly at these altitudes without oxygen and above the airplane's maximum gross weight.

Text from the NTSB. Open the NTSB docket for CEN11FA479 for the full record.