Accident Overview
On November 9, 2023, at approximately 0930 mountain daylight time, a Textron Aviation Inc. 172S (registration N1817E) was substantially damaged during a forced landing near Erie, Colorado. The flight instructor and student pilot were not injured. The aircraft was operated under Title 14 Code of Federal Regulations Part 91 as an instructional flight.
Pre-Flight and Engine Start
Following a thorough pre-flight inspection, the flight instructor started the engine. The engine began to shake, and the alternator was not charging the battery. The instructor shut down the engine and inspected both the engine and alternator belt, finding everything normal. After a second start, all indications were in the green, and the engine no longer shook. The run-up appeared normal.
Simulated Emergency and Descent
The flight departed. After completing several maneuvers, the instructor simulated an engine fire. The crew completed the appropriate checklists and began a simulated emergency descent starting at about 7,000 ft msl. They transitioned into a simulated emergency landing, with the student pilot selecting a field and descending to about 700 ft agl.
Emergency Landing and Impact
As the student pilot applied full power to recover from the simulated emergency, the engine began to shake again. The flight instructor took control and observed decreasing engine rpm. The engine still running, the instructor maneuvered toward an airport. He set up for a landing on a runway but found the aircraft too high and fast, with engine rpm reduced to about 1,900. To avoid houses near the airport, the instructor decided to land in a field.
The instructor maneuvered the aircraft into a field for an uneventful touchdown. However, the field sloped downward, and during the landing roll, the aircraft rolled nose-first into a culvert. The impact with the culvert caused substantial damage to the right wing and engine firewall.
Post-Accident Engine Examination
During the engine examination, compression was observed in cylinders No. 1, 2, and 3, but no compression in No. 4 cylinder. Further examination revealed that the No. 4 exhaust valve was stuck open and the No. 4 push rod was bent. A borescope examination showed no additional anomalies. Both magnetos produced sparks at all leads when the engine was rotated by hand at the propeller flange. The spark plugs appeared normal per the Champion Aviation Check-a-Plug Chart AV-27. All fuel injectors were clear.
Maintenance Records
A review of maintenance records revealed that Lycoming Mandatory Service Bulletin 388C, "Procedure to Determine Exhaust Valve and Guide Condition," had not been complied with as suggested by the engine manufacturer. The service bulletin stated that an inspection should be performed every 1,000 hours of operation if Hi-Chrome exhaust valve guides are installed. The inspection is intended to identify excessive carbon build-up between the valve stem and the valve guide to prevent sticking valves or valve failure. The accident airplane had Hi-Chrome exhaust valve guides installed, identified by the letter "C" stamped inside a circle on the engine cylinders.