What happened
On August 14, 1962, a Cessna 140, registration HB-CAI, was performing a private flight from Stuttgart-Böblingen to Lausanne. The flight included a stop in Konstanz for customs clearance. While flying near Bern under favorable weather conditions, the pilot experienced severe engine vibrations and observed the oil pressure gauge dropping toward zero.
Unable to reach Bern Airport due to the deteriorating engine condition, the pilot attempted an emergency landing in a meadow near Allmendeingen. Although the aircraft initially touched down normally, the right wheel became trapped in a drainage ditch approximately 85 meters along the landing strip, causing the aircraft to capsize. The two occupants, the pilot and a passenger, escaped the wreckage without injury.
The investigation
Investigators examined the wreckage of the Cessna 140 and the engine, a Continental C-90-12-F. The inspection revealed extensive internal damage to the engine, including a destroyed connecting rod, piston, and cylinder number one, as well as damage to the engine casing and bearings.
Evidence of oil loss was found along the fuselage, stretching approximately 50 cm from the filler neck toward the tail. Notably, the oil filler cap was found lying loose within the engine cowling. The investigation also noted that a clamping screw on an intake valve pushrod tube had become loosened.
Findings
- The primary cause of the accident was a connecting rod failure resulting from significant oil loss during flight.
- The oil loss originated from two points: a large amount escaping from the filler neck and a smaller amount from a loosened valve pushrod tube connection.
- It is highly probable that the pilot failed to properly secure the oil tank cap during pre-flight preparations the previous evening.
- While the engine failure was the direct cause, the investigation noted that the developing issue might have been detectable via rising oil temperatures or dropping pressure before the catastrophic mechanical failure occurred.