Incident Overview
On 30 June 2023 at 1830Z, a Piper PA28-161 (Warrior III), registration ZS-OVY, departed from Chief Dawid Stuurman International Airport (FAPE) for a night navigation training flight under Part 141 regulations. The aircraft was occupied by an instructor and a student pilot. The intended landing was at the same departure airport.
Sequence of Events
While overhead the northern suburbs of Grahamstown and climbing past approximately 4200 feet (2000 feet AGL), the crew heard a loud bang followed by a drastic drop in engine RPM and airframe vibration. The instructor assumed control and, with Grahamstown Airport's Runway 34 in sight, executed a forced landing. The aircraft came to rest safely on the centerline about three-quarters down the runway. No persons were injured, and the aircraft was not damaged during the landing. However, post-incident inspection revealed damage to the engine cowling from the cylinder head separation, loss of oil from pushrod shrouds, and slight exhaust riser damage. The aircraft had substantial damage overall.
Investigation Findings
The engine, a Lycoming, experienced a complete separation between cylinder number 2's steel barrel and aluminum head. The head material cracked, eventually breaking off. There were signs of an initial crack indicated by blowby residue from combustion gases escaping through a section about one quarter of the circumference of the cylinder barrel. The exact cause of the crack was not determined, but the cylinder assembly manufacturer had previously encountered similar issues (see FAA AD2007-04-19R1 and Superior Air Parts SB 0601). The crack was located in an area covered by baffles, making visual detection difficult.
The aircraft's last annual inspection was on 4 June 2023, 11.5 flight hours prior to the incident, and a compression test had shown good results on all four cylinders. The engine had accumulated 1504.3 hours since overhaul, with a TBO of 2200 hours.
Conclusion
The engine malfunctioned due to power loss caused by a cylinder head failure from a fatigue crack. The crack originated in a region between cylinders, hidden by inter-cylinder baffles. The aircraft was maintained in accordance with the Piper Maintenance Manual and general maintenance requirements. No other factors were identified.