Accident Overview
On September 11, 2019, at 1032 eastern daylight time, a Piper PA-28 airplane, registration N2890T, was destroyed in an accident near Boca Raton, Florida. The pilot received minor injuries and one passenger sustained serious injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pre-Accident Events
The pilot reported departing on a cross-country flight with full fuel. As the airplane reached about 500 ft, the engine began running rough. He returned to the airport and landed without further issue. With the assistance of a local mechanic, a visual inspection and an engine run were performed, but no anomalies were found and no maintenance was conducted. The pilot and mechanic then elected to perform a local flight. During the initial climb, at about 400 ft, the engine again ran rough. The pilot turned back toward the airport, and the engine subsequently lost total power. The airplane descended and impacted trees.
Engine and Systems Examination
The airplane was powered by a Continental Motors TSIO-360-FB turbocharged engine. The turbocharger's original ground-adjustable wastegate had been replaced with a Merlyn Black Magic Upper Deck Pressure Controller. The airplane also had a J.P. Instruments (JPI) EDM 700/800 engine data monitor that recorded exhaust gas temperatures (EGT) and cylinder head temperatures (CHT) for all six cylinders, as well as turbine inlet temperature (TIT).
Examination of the engine and airframe identified unidentified debris, similar in size to sand particles, within the throttle and fuel metering assembly, but all orifices were clear. The turbocharger remained attached, with impact damage and corrosion from fire suppressant chemicals; turbine and compressor blades showed normal operating signatures and could rotate. The exhaust system had impact damage but no signs of leaks; the induction system also had impact damage without leaks. Further examination revealed corrosion on exhaust fittings but no preimpact failures or blockages.
The Merlyn automatic wastegate works pneumatically, measuring differential pressure between manifold and upper deck pressure to adjust automatically. The wastegate did not hold vacuum; the diaphragm fabric had a small hole at its bottom, rendering the diaphragm inoperative and causing the valve to be in the closed position. According to Merlyn personnel, a closed wastegate would increase manifold pressure for a given throttle setting compared to normal operation, and such a failure might not be perceived by the pilot. No other anomalies were found that would have prevented normal operation.
Data Analysis
The EDM recorded data from three sessions on the day of the accident. In the first session, TIT dropped about 1,300° for about one minute, then spiked and paralleled EGTs. Shortly after, EGTs and CHTs showed sharp temperature changes and then a steady drop. The second session showed no anomalies. The third session, correlating to the accident flight, showed TIT dropping rapidly about 13 minutes into the recording; CHT and EGT remained steady for about one minute, then EGT dropped rapidly and CHT declined steadily. Previous sessions had shown TIT drops but without unusual power losses.
Probable Cause
Not stated in the source.