CEN24FA170 · Zenith CH601 HDS

The private pilot and pilot-rated passenger were returning to their home airport following a personal flight. About 7 miles from the destination airport, the airplane’s airspeed increased, and it entered a steep descent. Witnesses reported that the airplane descended rapidly and impacted a wooded area. Witnesses also reported conflicting observations regarding whether the engine was operating normally. The engine examination did not reveal any preimpact anomalies, and the shattered and widely dispersed wooden propeller blade fragments were consistent with engine power at impact. The airframe examination did not reveal any preimpact mechanical malfunctions or failures that would have precluded normal operation. Toxicological testing of the pilot identified ethanol at low levels in several of the specimens and was not detected in brain tissue. Based on these results, some or all of the small amount of detected ethanol may have been from postmortem production rather than alcohol consumption, and it is unlikely that ethanol effects contributed to the accident. As a result of his heart disease, the pilot was at some increased risk of a sudden impairing or incapacitating cardiac event, such as chest pain, arrhythmia, or heart attack. The autopsy identified no evidence of such an event. However, an acute cardiac event occurring immediately before death may leave no reliable autopsy evidence. Whether the pilot’s heart disease contributed to the accident could not be determined. Toxicological testing of the pilot-rated passenger identified two oral medications commonly used to treat diabetes. People with medication-treated diabetes are at risk for both abnormally high blood sugar (from diabetes) and abnormally low blood sugar (from medication effects). Short-term effects of high blood sugar may include decreased cognitive performance, including slower information processing speed, decreased executive function and attention. Low blood glucose may cause difficulty concentrating, impaired task performance, and, in extreme cases, diminished consciousness, seizure, and death. The pilot-rated passenger’s postmortem urine glucose concentration is inconsistent with a markedly high antemortem blood glucose; however, it provides no information about whether his blood sugar may have been low. It also is unknown if the pilot-rated passenger had less severe symptoms of diabetes, such as fatigue or blurred vision or chronic complications associated with diabetes, such as vision loss, neuropathy, or kidney disease. As a result of his heart disease, the pilot-rated passenger was at some increased risk of a sudden impairing or incapacitating cardiac event, such as chest pain, arrhythmia, or heart attack. The autopsy identified no evidence of such an event. However, such an event does not leave reliable autopsy evidence if it occurs immediately before death. It is unknown what role the pilot-rated passenger had, if any, in aircraft operations and flight safety. Whether the effects of the pilot-rated passenger’s use of metformin and glipizide or his heart disease contributed to the accident cannot be determined. Although either occupant could have experienced a sudden incapacitating medical event while manipulating the flight controls during the descent, the remaining occupant may have had insufficient time or opportunity to recover the airplane before impact. However, the investigation could not determine which occupant, if either, was manipulating the flight controls at the time of the accident. Therefore, whether either occupant experienced an incapacitating medical event that contributed to the accident could not be determined.

Verbatim NTSB analysis and probable cause from the NTSB dataset