Incident Sequence
On May 8, 2024, at approximately 1130 eastern daylight time, a Piper PA-32-300, registration N908DK, was substantially damaged in a forced landing near Apopka, Florida. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The company pilot and the pilot/owner were not injured.
The flight originated from Bartow Executive Airport (BOW) to Orlando Executive Airport (ORL), where the company pilot picked up the pilot/owner. After an uneventful flight, the pilots intended to return to BOW. During the climb to 2,500 ft mean sea level, the engine began to run roughly. The company pilot observed that two cylinders had stopped producing power. As the pilot/owner looked up the common traffic advisory frequency for the nearest airport, two additional cylinders lost power, and the airplane could not maintain altitude. The company pilot executed a forced landing; during the landing, the left wing struck a tree, resulting in substantial damage.
Postaccident Examination and Testing
A Federal Aviation Administration inspector examined the wreckage and found fuel in all wing fuel tanks. All cylinders exhibited compression, and a visual inspection of the engine revealed no preaccident anomalies. The engine was sent to the manufacturer for further examination and a test run.
Data extracted from the onboard avionics indicated that, beginning 5 minutes and 15 seconds after rotation, the exhaust gas temperature (EGT) on the No. 2 cylinder dropped. Subsequent drops occurred on cylinders 4, 3, and 6. Engine rpm began to decrease from 2,380 at 1129:13, continuing until impact. The data also showed that the oil temperature reached a maximum of 231°F during the flight.
During the test run at the manufacturer’s facility, the engine was started and warmed to approximately 250°F at 2,000 rpm. The oil filter adapter with the thermostatic oil cooler bypass valve (vernatherm) was removed and replaced with a substitute. The engine then completed a full power test. All parameters passed except airflow at rated power, which measured 1,535.3 pounds per hour, slightly below the low limit of 1,636.6 pph. The manufacturer noted that this power deficiency was not likely noticeable during normal operation. Visual examination of the original oil filter adapter revealed a non-uniform witness mark on the valve, consistent with improper seating. An improperly seated valve could allow hot oil to bypass the oil cooler, producing elevated oil temperatures similar to those observed during the test run.
An examination of the airframe by the manufacturer found no preaccident obstructions or leaks in the fuel system. The fuel selector, boost pump, and flow transducer functioned normally. The spark plugs showed normal electrode wear but were darker than typical, consistent with an excessively rich fuel-air mixture. The exhaust valve springs were intact. The exhaust valve stems of cylinders 2 through 6 had moderate carbon buildup on the combustion chamber side of the exhaust guide. The exhaust valve stem of cylinder 4 was tight when pushed into the cylinder head.
Historical Data and Maintenance Findings
The pilot/owner reported that the airplane experienced cylinder failures in flight on three occasions in 2023 (March, April, and May), each requiring an emergency landing. Maintenance work orders indicated that after the March event, the maintenance provider suspected bad fuel or improper mixture. After the April event, the No. 6 cylinder nozzle and spark plugs were cleaned, and a new starter was installed. After the May event, the work order stated "reassembled aircraft after engine quit due to bad cylinder."
Personnel at the maintenance facility stated they did not review data from the engine monitoring device (EMD) during troubleshooting, noting that they normally do not examine it unless provided by the customer. The avionics had been installed in February 2022, and the shop had completed two annual inspections and an examination after an engine issue since then.
Historical EMD data revealed similar EGT drops on multiple flights, coinciding with the reported engine malfunctions. The data also showed that the airplane’s oil temperature had exceeded 220°F multiple times since August 2022, with a maximum of 247°F. The Lycoming Operator’s Manual specifies a maximum permissible oil temperature of 245°F and a desired range of 165°F to 200°F.
A review of maintenance logbooks indicated that the engine was last overhauled on November 1, 1997. Between the 2018 and 2024 annual inspections, the airplane accumulated 84 hours. The most recent annual inspection on February 13, 2024, included replacement of the No. 1 cylinder. No other cylinder replacements were noted since the 1997 overhaul. There was no documentation of compliance with Lycoming Service Bulletin 388, which recommends inspections for valve sticking, or Lycoming Service Instruction 1485, which recommends replacing exhaust guides with improved material. Lycoming Service Instruction 1009 recommends engine overhaul within 12 calendar years.