ERA24LA211 · Piper PA32 300

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.

Verbatim NTSB analysis and probable cause from the NTSB dataset