ERA24LA211

A partial loss of engine power due to sticking exhaust valves. Contributing to the accident was maintenance personnel’s failure to use available engine data while troubleshooting a known engine issue and maintenance personnel’s failure to comply with inspections called out in a relevant service bulletin.

After departing, the pilots initiated a climb to 2,500 ft mean sea level (msl), during which the engine began to run “rough.” One of the pilots noticed that two cylinders had stopped producing power and he asked the pilot/owner to look up the common traffic advisory frequency for the closest airport. An emergency radio transmission was made and the pilot/owner noticed that two more cylinders had stopped producing power and the airplane was unable to maintain altitude. The other pilot identified an area and performed a forced landing, during which the left wing struck a tree and sustained substantial damage. Postaccident review of engine data for the flight showed that the exhaust gas temperatures (EGT) of the Nos. 2, 3, 4, and 6 cylinders dropped excessively. These drops in EGT and subsequent loss of cylinder head temperatures (CHT) were consistent with the cylinders failing to produce power. Additionally, the data showed that the oil temperature reached a maximum of 231° F (the engine manufacturer’s maximum permitted oil temperature was 245° F). Postaccident examination of the airplane found the thermostatic oil cooler bypass valve in the oil filter adapter was not seating properly and was allowing hot oil to partially bypass the oil cooler, increasing the temperature of the engine. When the oil filter adapter was replaced, the engine was successfully test run according to manufacturer’s standard power and leak engine run test. The test also revealed that the engine airflow limit was below the designated range, which would result in the engine having slightly less power and a richer fuel/air mixture. The spark plugs were dark in color, which was also consistent with excessively rich fuel air/mixture engine operation. The airplane was also based and operated in an area that typically experienced high ambient temperatures and was operated using leaded fuel; two factors that could contribute to an increased rate of oil contaminant accumulation. An examination of the engine exhaust valve stems found buildup of carbon on the combustion side of the exhaust guides in five cylinders. Given this information, the rich mixture and elevated oil temperature likely led to the buildup of carbon and coked oil that resulted in the sticking of multiple exhaust valves during the accident flight. The pilot/owner reported that there had been three previous events during which the engine lost power in the cylinders; each time the engine was returned to service by the maintenance provider. Historical data from the engine monitoring device showed cylinder behavior consistent with the accident flight. Specifically, during those flights, the oil temperatures were near or in excess of the engine manufacturer’s limit. Maintenance personnel reported they had not reviewed at the historical engine data during troubleshooting or before returning the airplane to service. It is possible that if maintenance personnel reviewed the engine data they could have identified the high oil temperature trend and correlated it to the multiple losses of power in individual cylinders. Additionally, a review of the airplane’s maintenance logbooks revealed that the engine was 15 years past the manufacturer’s recommended time between overhaul. There was no evidence that an engine manufacturer service bulletin related to determining exhaust valve and guide condition was complied with, nor, based on the logbooks and date of overhaul, is it likely that improved design exhaust valve guides were installed on the engine. Had the valve guide inspections called for in the service bulletin been complied with, it is likely that the oil coking and carbon buildup, that were the likely result of the rich engine operation and high oil temperature, would have been detected and addressed before resulting in the losses of power that were observed on the accident and previous flights.

On May 8, 2024, about 1130 eastern daylight time, a Piper PA-32-300, N908DK, was substantially damaged when it was involved in an accident near Apopka, Florida. The company pilot and -pilot/owner were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The airplane sustained a loss of engine power on April 4, 2023. Maintenance was performed over the next 10 months and an annual inspection was completed on February 13, 2024. On the day of the accident, a pilot employed by the company that performed the maintenance flew the airplane (company pilot) from Bartow Executive Airport (BOW), Bartow, Florida, to Orlando Executive Airport (ORL), Orlando, Florida, where he picked up the pilot/owner. The flight was uneventful. The pilots intended to return to BOW, where the pilot/owner would pay his bill before flying the airplane back to the airport where it was based. After departure, the pilots initiated a climb to 2,500 ft msl, during which the engine began to run “rough.” The company pilot noticed that two cylinders had stopped producing power and asked the pilot/owner to look up the common traffic advisory frequency for the closest airport, which he did. An emergency radio transmission was made and the pilot/owner noticed that two more cylinders had stopped producing power and the airplane was unable to maintain altitude. The company pilot performed a forced landing, during which the left wing struck a tree and sustained substantial damage. Postaccident examination of the wreckage by a Federal Aviation Administration inspector found fuel in all wing fuel tanks. Compression was observed on all cylinders, and the engine was visually inspected with no preaccident anomalies noted. The engine was subsequently sent to the manufacturer’s factory for continued examination and a test run. Before the test run, data that included engine data parameters were extracted from the onboard avionics. The data showed that, 5 minutes and 15 seconds after rotation, at 1125:00, the exhaust gas temperature (EGT) on the No. 2 cylinder began to reduce. At 1126:34, the No. 4 cylinder EGT began to drop, followed by the No. 3 cylinder EGT at 1126:45. The No. 6 cylinder EGT began to fluctuate up and down at 1127:38, before eventually dropping at 1129:20. At 1129:13, the engine rpm began to reduce from 2,380 and continued to drop until impact. The data also showed that the oil temperature during the flight reached a maximum of 231° F. As the EGT in the cylinders dropped, the cylinder head temperatures (CHT) also began to drop. A test run was performed at the manufacturer’s factory. During the test run, the engine was started and warmed up with the oil temperature reaching approximately 250° F by the time the engine was about 2,000 rpm. The engine was shut down and the oil filter adapter, with the thermostatic oil cooler bypass valve (vernatherm), was removed and a substitute oil filter adapter was installed. The engine run was completed with the engine operating through its full power band following the manufacturer’s standard power and leak engine run test. All areas passed except for the air flow limits at rated power. The low limit was 1,636.6 pounds per hour (pph); the test result was 1,535.3 pph. The manufacturer reported that the airflow number would equate to the engine being slightly low on power but was not low enough that they would expect a pilot to be able to discern a difference during normal operation of the airplane. Visual examination of the original oil filter adapter and the thermostatic oil cooler bypass valve revealed a witness mark of the valve that was not uniform, consistent with the valve not seating properly. An improperly seated valve would allow hot oil to partially bypass the oil cooler, resulting in excess oil temperatures consistent with those found when the engine was run on the test stand with the original oil filter adapter. A subsequent examination of the airplane was conducted with the airframe manufacturer. The examination found no preaccident obstructions or leaks in the fuel system. The fuel selector remained installed in the airframe. Air was applied through the fuel system, confirming appropriate flow in all fuel selector positions. Each fuel selector position exhibited a tactile detent. The fuel selector valve/fuel strainer screen was unobstructed. The fuel boost pump was tested and ran smoothly when external power was applied. The fuel flow transducer remained attached to the airframe and was removed and checked for blockages. The transducer was unobstructed and the fuel flow measuring wheel rotated normally. The spark plugs were removed and the electrode wear appeared normal. The spark plug electrodes were visibly darker than normal, consistent with an excessively rich fuel to air ratio. The exhaust valve springs were dark in color and were intact on all cylinders. The exhaust valve stem of cylinder No. 1 appeared clean, with no buildup or residue noted. The exhaust valve stems for cylinder Nos. 2, 3, 4, 5, and 6 had moderate buildup of carbon at the combustion chamber side of the exhaust guide. The exhaust valve stem of cylinder No. 4 caught and was tight when it was pushed into the cylinder head. The pilot/owner reported that in March 2023 the airplane had “lost” a cylinder in flight and an emergency landing was performed to a local airport. He contacted his maintenance provider, who reported to him over the phone that it was likely bad fuel or an improper mixture setting. He also reported that in April 2023 the airplane again exhibited cylinders shutting down in flight; again, an emergency landing was performed to a local airport. A maintenance work order indicated that the maintenance facility installed a new starter and cleaned the No. 6 cylinder nozzle and spark plugs, and then the airplane was put back into service. In May 2023 the airplane again exhibited cylinders shutting down in flight and the pilot was forced to make an emergency landing on a roadway. The airplane was recovered and taken to the maintenance facility. The work order for the work performed after this incident stated, in part, “reassembled aircraft after engine quit due to bad cylinder.” Personnel at the maintenance facility were asked if, during their troubleshooting of the engine, they reviewed the available data from the engine monitoring device (EMD). Their initial response was “…no. He had just put in a Garmin 1000 and there was no engine monitoring system when we did the last annual.” The avionics had been installed in February 2022, and since that time the maintenance shop had completed two annual inspections and an examination after a reported engine issue. The maintenance personnel further stated, “We don't normally look at engine monitoring, if we do, the customer has provided it to us.” A review of historical data recovered from the EMD revealed similar cylinder EGT drops on multiple other flights. These flights coincided with the other engine malfunctions the pilot/owner reported. The historical data also revealed the airplane oil temperature had exceeded 220° F multiple times since August 2022, with a maximum recorded oil temperature of 247° F. The Lycoming Operator’s Manual stated, “The maximum permissible oil temperature is 245°F (118°C). For maximum engine life, desired oil temperature should be maintained between 165°F (73.8°C) and 200°F (93.3°C) in level flight cruise conditions.” A review of maintenance logbooks showed that the engine was last overhauled on November 1, 1997. From the annual inspection in 2018 to the annual inspection in 2024, the airplane had accumulated 84 hours. The most recent annual inspection was completed on February 13, 2024. During this annual inspection, the No. 1 cylinder was replaced. The logbook entry stated the No. 2 cylinder had been replaced but the shop reported that this was a “typo” and it was,