Greenville, SC, USA
N121YT
FLIGHT DESIGN CTLS
The pilot was nearing his destination airport on the first flight after a condition inspection was completed when the engine oil pressure dropped to zero. He declared an emergency and attempted to divert to a closer airport; however, after about 4-5 minutes the engine lost power. Once he realized he would not be able to glide to an airport, the pilot deployed the ballistic parachute system at about 500 ft above ground level. The airplane descended into trees, resulting in substantial damage to the fuselage and left wing. A postaccident examination of the engine found the hoses from the oil tank to the thermostat and from the thermostat to the oil cooler had disconnected. The examination also found that the No. 3 connecting rod bearing displayed failure signatures consistent with a lack of lubrication. The valvetrain components in the cylinder head and the cylinder bores were dry due to a lack of lubrication. Based on this information, it is likely that the disconnection of the oil lines from the thermostat prevented oil from reaching critical components within the engine and subsequently resulted in the failure of the No. 3 connecting rod bearing. A review of maintenance records showed that the airplane’s annual condition inspection was completed two days before the accident flight. The review also found that the oil system hoses had been replaced a year prior as required by the engine manufacturer, and that the airframe had accumulated 152 flight hours since the hoses were replaced. The mechanic who performed the annual condition inspection reported that he did not remove any hoses from the thermostat. The mechanic reported checking the hoses for security, and that they did not come off when tugged on. The investigation was unable to determine why the oil hoses became disconnected from the oil thermostat in flight.
On October 10, 2021, at 1210 eastern daylight time, a Flight Design GMBH CTLS, N121YT, was substantially damaged when it was involved in an accident near Greenville, South Carolina. The private pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, an annual condition inspection was conducted at Twin Lakes Airport (S17), Graniteville, South Carolina. He conducted a preflight inspection of the airplane with no anomalies noted and departed for Henderson, North Carolina. About 18 mile south of his destination, the engine oil pressure dropped to zero. The pilot turned towards Greenville Downtown Airport (GMU), Greenville, South Carolina, and declared an emergency. The pilot reported that the engine continued to run for about 4 or 5 minutes before it “seized.” The pilot then reported to GMU that he would not be able to make the airport and turned towards an open clearing before deploying the ballistic parachute about 500 ft above ground level (agl). Shortly after deploying the parachute, the airplane descended into pine trees and was suspended about 50 ft above the ground about 9 miles north of GMU. The pilot climbed out of the side window and was rescued by local first responders. A postaccident examination of the airplane by a Federal Aviation Administration inspector revealed substantial damage to the fuselage and left wing. The airplane was recovered to a secure facility and examined. The engine was found to be in good overall condition with oil staining down the right side of the airplane from the engine cowling to the horizontal stabilizer. The hose from the oil tank to the oil thermostat and the hose from the oil thermostat to the oil cooler were found disconnected from the oil thermostat (figure 1). The hoses and barbs were undamaged and intact, and the hose clamps remained installed on the hoses. A representative for the engine manufacturer reported that, with the hoses to and from the oil thermostat disconnected, it would be reasonable to expect that the engine would seize after about 3 to 4 minutes at maximum power due to the loss of lubrication that would occur. The valvetrain components in the cylinder heads were dry and lacked lubrication, and the No. 1 valve cover had metallic debris inside. There were no other anomalies noted within the cylinder heads or their components. All cylinders were removed and the cylinder bores were dry without any oil lubrication. The crankshaft could not be rotated by hand. After removing the cylinders, it was found that the No. 3 connecting rod bearing failed and was discolored consistent with exposure to excessive heating. The No. 3 piston and connecting rod were removed and the crankshaft rotated by hand. Approximately 2.5 quarts of oil were drained from the oil tank. The oil cooler system was not breached or damaged. Figure 1 - View of the oil thermostat and disconnected oil hoses. Data recovered from a Dynon EMS-D120 engine data monitor showed that, about 62 minutes after recording began on the accident flight and about 53 minutes after takeoff, the oil pressure dropped from 51 pounds per square inch (psi) to 0 psi in 55 seconds and remained about 0 psi for the remainder of the recording. The data also showed that the engine rpm decreased from about 5300 rpm, when the oil pressure drop was first noted, to 0 rpm over the course of about 5 minutes. The data were consistent with the pilot’s description of the flight and the loss of engine power. Review of the airplane’s maintenance records showed a condition inspection was completed two days before the accident, on October 8, 2021. The accident flight was the first flight after this inspection was completed. The mechanic who inspected the airplane reported that he did not remove any hoses from the oil thermostat, that he checked them for security before returning the airplane to service, and that they did not come off when he “tugged” on them. On October 14, 2020, the rubber hoses servicing the engine’s oil and fuel systems were replaced in accordance with the engine manufacturer’s 5-year requirement. The airframe had accumulated 152 hours since that work was completed.
A total loss of engine power resulting from the in-flight disconnection of oil hoses from the oil thermostat.
Source: NTSB Aviation Accident Database
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