PIPER AIRCRAFT INC PA46R-350T — Mooresville, NC

What happened

The pilot departed his home airport for a short local flight. According to ADS-B data, the airplane flew for about 10 minutes before it began a return to the departure airport. About 8 minutes after turning back toward the airport, the airplane had a sudden decrease in groundspeed and began a descent. At the airplane’s last ADS-B position, it was at an altitude of 60 ft above ground level (agl) and less than 1 nautical mile (nm) from the threshold of the airport’s runway. The airplane subsequently struck trees about 40 ft agl, which separated the left elevator, and the airplane came to rest about 58 ft from the trees. A witness near the accident site reported hearing no engine noise from the airplane before impact. A sound spectrum study of audio captured by a security camera near the accident site revealed that, just before impact, the airplane’s propeller was rotating at a rate near 1,100 rpm, which was consistent with the engine at idle or windmilling.

A postaccident examination of the airframe and engine revealed that an induction clamp was missing that connected the induction hose to the left side intercooler, and the induction hose coupling was displaced from the intercooler inlet. The induction clamp was not observed during any of the postaccident examinations. All spark plugs were carbon fouled, which was consistent with the engine operating with an overly rich fuel/air mixture. Although the fuel servo testing revealed that the servo was slightly rich at two test points, this small amount of excess fuel flow would not have precluded normal operation of the engine. Testing of the fuel pump revealed that it operated normally at all tested conditions except for the 650 rpm setting, which resulted in a low flow rate of 2 lbs per hour (below the specified 9 lbs per hour). However, the flow rate at 1,100 rpm was 90 lbs per hour, which would have been sufficient flow to support engine operation at idle rpm in flight. No other anomaly was found.

Generally, when an induction hose that is downstream of a turbocharger compressor is disconnected from the rest of the induction system, the engine potentially loses a significant amount of manifold pressure. Based on the available information, it is likely that, due to the missing clamp, the induction hose coupling became disconnected from the left side intercooler, which resulted in an imbalance in the intake system, and the fuel mixture becoming overly rich. This would subsequently result in a loss of engine power. The reason the clamp was missing could not be determined as the clamp was not recovered.

The postaccident toxicological testing results for samples from the pilot indicated that he had used the medication diphenhydramine, which has a potential to cause sedation and impairing effects. Although the pilot may have been experiencing impairing effects of the medication at the time of the accident, no more specific conclusions about his impairment could be drawn. Additionally, his autopsy report indicated cardiovascular disease, which is associated with increased risk of experiencing a sudden impairing or incapacitating cardiovascular event, such as heart attack or stroke. There was no autopsy evidence that such an event occurred; however, such an event does not leave reliable autopsy evidence if it occurs immediately before death.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.