What happened
On August 14, 2025, at 17:14 CDT, a Piper PA-18-150, registration N476SM, was performing a banner tow flight under Part 91 regulations near Joliet, Illinois. The pilot had departed for a scheduled three-hour mission when, approximately two hours into the flight, a loud bang was heard from the engine.
This event was followed by intense vibrations and a progressive loss of engine power, eventually leading to a total loss of power. The pilot performed a forced landing into a field. During the landing roll, the aircraft ground looped and struck a fence, causing substantial damage to the left elevator. The pilot was not injured.
The investigation
An FAA inspector noted engine oil present on the underside of the fuselage, extending from the engine cowling to the empennage, and observed oil leaking from the engine exhaust pipe.
Post-accident examination of the engine determined that the No. 2 cylinder exhaust valve failed. The investigation found that while the valve head was destroyed inside the cylinder, the majority of the valve stem remained within the valve guide. No other mechanical malfunctions or anomalies were identified that would have prevented normal engine operation.