What happened
On July 21, 1968, a Piper PA-18-180, registration HB-ORW, departed Kloten airport for a local aerial traffic monitoring mission. During the flight over the lower Lake Zurich basin near Wollishofen, the engine suddenly began to vibrate and shake violently. The failure caused oil to spray across the windscreen, instantly obscuring the pilot's forward vision.
To regain visibility, the pilot opened the upper door wing and shut off the ignition. Recognizing that an immediate landing was necessary, the pilot bypassed nearby populated areas to avoid risking lives on the ground and instead opted for an emergency water landing on Lake Zurich between Zollikon and Tiefenbrunn. The pilot executed a high-speed approach at a sharp angle to the water. The aircraft glided across the surface before coming to a halt. The pilot and passenger were able to exit the aircraft safely before it sank to a depth of 35 meters.
The investigation
Investigators examined the engine components and maintenance records of the Piper PA-18-180. The investigation focused on the sudden increase in oil consumption observed in the weeks leading up to the accident. While the aircraft had recently undergone an engine upgrade to a 180 HP Lycoming engine, the investigation found that the takeoff weight for this flight was at least 70 kg above the maximum allowable limit.
Findings
- The primary cause of the engine failure was the destruction of the number two connecting rod bearing.
- This failure was likely triggered by a lack of lubrication or the breakage of an oil regulating ring.
- The investigation determined that the engine's oil consumption had risen to approximately 0.714 liters per hour, which exceeded the manufacturer's maximum recommended limit for that power setting.
- The pilot did not perform a proper oil level check prior to engine start, only noticing low oil pressure while taxiing.
- The engine's maintenance oversight contributed to the failure, as the rising oil consumption was not identified or addressed by the operator or maintenance staff.
- The engine was also equipped with an unauthorized muffler at the time of the accident.