Northwing Design APACHE SPORT N51311 accident near Taos, New Mexico

Probable cause

The powered-lift aircraft's departure from controlled flight for reasons that could not be determined from the available information.

NTSB analysis

The 69-year old sport pilot, who had over 300 hours of flight experience in the accident airplane, successfully took off in his powered lift aircraft. Several witnesses who were working on the departure end of the runway reported seeing the aircraft take off from the runway, climb to about 500 ft, and then enter a right turn. The witnesses stated that the aircraft seemed to "fall out of the sky." One witness reported hearing the engine revving. Postaccident examination revealed no preimpact mechanical failures or malfunctions with the aircraft or the engine that would have precluded normal operation.

The pilot's autopsy revealed that he had severe coronary artery disease with 80% stenosis in the proximal left anterior descending coronary artery. In addition, there was evidence of scarring, indicating some previous damage to the myocardium. This degree of coronary disease placed him at risk for acute ischemia, or limitation of blood flow to the heart muscle, which can cause chest pain, shortness of breath, or decreased blood pressure. Ischemia can also be associated with an arrhythmia, which can cause palpitations, shortness of breath, or fainting. The identified scarring further increased the likelihood that he experienced an arrhythmia. None of these events would have left visible evidence on the autopsy.

The autopsy also revealed that the pilot had "extensive" emphysema or chronic obstructive pulmonary disease (COPD). Further, his wife reported that he had shortness of breath and used an inhaler to treat it. Significant COPD is commonly associated with the development of pulmonary hypertension or elevated pressures affecting the right side of the heart, which can lead to significant hypertrophy of the right side of the heart without affecting the left side. This likely caused the pilot's 0.7-cm-thick right ventricular wall, which was more than twice the average thickness. Although the severity of the pilot's pulmonary hypertension could not be determined by the postmortem evaluation, the combination of pulmonary hypertension and COPD significantly increased the pilot's risk of an acute cardiac event. Given the circumstances of the accident and the pilot's cardiac conditions, it is possible that he became acutely impaired or incapacitated by symptoms from his cardiac disease and that could have resulted in the loss of aircraft control. Given the lack of evidence on autopsy of a medical event occurring and given the limited witness observations, it could not be determined whether the loss of control was the result of incapacitation or if there was another reason that the aircraft departed controlled flight and the pilot was unable to regain control of the aircraft.

Toxicology tests showed that the pilot used zolpidem, which is used as a sleep aid and is acutely impairing. However, based on the available information and the tested specimen, it could not be determined whether effects from the pilot's use of zolpidem contributed to the accident. The pilot's toxicology results also indicated that he had used marijuana some time before the flight. However, tetrahydrocannabinol can undergo significant postmortem redistribution, which could have elevated or decreased the postmortem levels. As a result, the investigation could not determine whether effects from the pilot's use of marijuana contributed to the accident.

Text from the NTSB. Open the NTSB docket for CEN15FA277 for the full record.