Boca Raton, FL, USA
N2890T
Piper PA28
Following a partial loss of engine power after takeoff, the pilot returned to the airport and performed a visual inspection and engine test run with a mechanic, which revealed no anomalies. The pilot then chose to perform another flight without identifying the cause of the loss of engine power and the mechanic agreed to accompany him. As the airplane climbed through 400 to 500 ft above ground level after takeoff, the engine ran rough, and the pilot started a turn back to the airport. The engine subsequently lost total power and the airplane impacted terrain and obstacles. The airplane was equipped with an engine monitor that captured exhaust gas temperatures (EGT), cylinder head temperatures (CHT), and turbine inlet temperature (TIT). TIT is the direct measurement of the temperature of combined exhaust from all cylinders immediately before it enters the turbocharger, but the measurement itself is not used in the normal operation of the turbocharger. The data showed a rapid drop in TIT about 45 seconds before changes in the CHT and EGT associated with both loss of power events on the day of the accident. The data also recorded three other sessions in which the TIT dropped similarly, but there were no associated changes to EGT or CHT values to indicate a loss of engine power on those occasions. No evidence was found to indicate a loss of engine power resulted directly from the changes in TIT or what caused those changes. Examination of the engine revealed a hole in the turbocharger’s automatic wastegate controller diaphragm, which would result in the wastegate failing toward the closed position. The closed wastegate would increase manifold pressure and decrease the efficiency of the turbocharger at higher altitudes; however, a closed wastegate would not result in a total loss of engine power. The reason for the loss of engine power could not be determined based on available evidence.
On September 11, 2019, at 1032 eastern daylight time, a Piper PA-28 airplane, N2890T, was destroyed when it was involved in an accident near Boca Raton, Florida. The pilot received minor injuries and one passenger received serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he departed on a cross-country flight with full fuel when the engine began running rough as the airplane reached about 500 ft. He returned to the airport and landed uneventfully. He troubleshot the engine problem with the assistance of a local mechanic, which was limited to a visual inspection and an engine run. They did not find any anomalies or perform any maintenance on the airplane. The pilot and the mechanic then elected to perform a local flight. During the initial climb, the engine again ran rough as the airplane reached about 400 ft. The pilot turned back toward the airport, and the engine subsequently lost total power. The airplane descended and impacted trees. The airplane was powered by a Continental Motors TSIO-360-FB turbocharged engine. The turbocharger’s original ground-adjustable wastegate was replaced with a Merlyn Black Magic Upper Deck Pressure Controller. The airplane was also equipped with a J.P. Instruments (JPI) EDM 700/800 engine data monitor. The EDM recorded exhaust gas temperatures (EGT) and cylinder head temperatures for cylinder Nos. 1 through 6 and Turbine Inlet Temperature (TIT). TIT is the measurement of the temperature of the exhaust gases entering the turbo unit on the engine. The measurement is for informational use only and is not used during the normal operation of the turbocharger. The EDM data was downloaded and 3 sessions from the day of the accident were recovered. The first recording on the day of the accident contained about 14 minutes of data. The EGT values remained parallel with each other throughout the recording. The TIT, reflected as TIT1 in the data, remained parallel with the recorded EGTs until about eight minutes into the session. TIT1 then dropped about 1,300° for about one minute before spiking up and down once and then paralleling the EGTs for the remainder of the session. EGTs and CHTs showed a sharp increase and decrease in temperature about 1 minute later, followed by a steady drop in both sets of data for about 1.5 minutes. The second recording captured about 3 minutes and 45 seconds of data; no anomalies were noted. The third recording, which correlated to the accident flight, captured about 14 minutes and 30 seconds of data. The EGT and TIT1 paralleled each other until about 13 minutes and 15 seconds, when there was a rapid drop in TIT1 temperature. CHT and EGT remained steady near 1300° for about one minute after TIT1 dropped, before EGT dropped rapidly and CHT began to decline steadily. The EDM data showed three previous sessions that reflected a drop in TIT1 values; however, EGT and CHT data did not indicate any unusual losses of engine power associated with the changes in TIT1 during those sessions. Examination of the airframe and engine revealed unidentified debris, similar in size to sand particles, within the engine throttle and fuel metering assembly. The throttle and fuel metering assembly were further examined, and all orifices were found clear of obstructions. The turbocharger remained attached and displayed impact damage as well as corrosion consistent with exposure to fire suppressant chemicals. The turbine and compressor blades displayed normal operating signatures and were capable of rotation. Upon initial examination, the exhaust system displayed impact damage signatures in the form of bending and crushing. No signs of exhaust leaks were identified. The induction system displayed impact damage signatures to some of the induction tubes; there was no indication of leaking. An additional examination of the exhaust system revealed corrosion on all fittings. The second examination of both cylinder banks exhaust did not reveal any preimpact failures or blockages. According to literature provided by Merlyn Products Inc., their automatic wastegate is a pneumatically- operated controller that measures differential pressure between manifold pressure and upper deck pressure and automatically adjusts accordingly to maximize engine and turbocharger efficiency. Examination of the wastegate revealed that the unit did not hold vacuum. The diaphragm fabric exhibited a small hole at the bottom of the diaphragm, which rendered the diaphragm inoperative and would have caused the valve to be in the closed position. According to Merlyn personnel, a valve that failed to the closed position would result in increased manifold pressure for a given throttle setting when compared to a wastegate that operates normally. The manifold pressure is controlled by the pilot, and a wastegate failure may not be perceived by a pilot. There were no further anomalies observed with the airframe or engine that would have prevented normal operation or production of rated horsepower.
The total loss of engine power for reasons that could not be determined based on available evidence and the pilot’s decision to take off without fully troubleshooting the partial loss of engine power that occurred during the previous flight.
Source: NTSB Aviation Accident Database
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