What happened
On the morning of the incident, a privately-operated Ayres S-2R spray plane, registered C-FBED, was returning to the Boston Brook, New Brunswick, airstrip after finishing its second spray mission of the day. While flying at an altitude of roughly 200 to 300 feet, the pilot noticed the engine began to vibrate and run roughly. The pilot contacted a maintenance engineer via radio to report the issue, but shortly after, white smoke began emitting from the left side of the engine, obscuring forward visibility.
As the engine ceased operation, the pilot attempted to maneuver toward a nearby cutover. However, the area was heavily populated with tree stumps, making it an unsuitable landing site as a nose-over was likely. With the engine dead and altitude rapidly decreasing, the pilot performed a forced landing into a stand of trees at the edge of the cutover. The aircraft sustained substantial damage, though the pilot escaped without injury and no fire occurred following the impact.
The investigation
The investigation focused on the sudden mechanical failure of the engine. Investigators confirmed that the engine had adequate lubricating oil and that the oil filter screens were clean, showing no signs of metal contamination. This ruled out oil supply issues or routine maintenance oversights as contributing factors. Furthermore, the propeller, accessory gearbox, and valve train were found to be functioning correctly prior to the failure.
Findings
- The engine failure was characterized by a rapid sequence of mechanical breakdowns.
- Damage to cylinder number five indicated that its connecting rod failed first.
- This initial failure caused the rod to penetrate the cylinder sleeve, triggering a chain reaction of overload failures in the remaining connecting rods.
- The specific cause for the failure of the fifth connecting rod could not be determined due to the extreme damage to the fracture surfaces.
- The low altitude of the aircraft at the time of the failure left the pilot with minimal time to prepare for the emergency or select an alternative landing site.