What happened
On June 25, 2003, at approximately 21:00 UTC, a Moravan Z-43, registration OK-WOK, departed from Brno on a return flight to Prague with a pilot and two passengers. During the flight near Humpolec, the pilot observed an oil pressure drop to zero. Because the engine continued to operate normally, the pilot believed the reading was a faulty indication and elected to continue the flight toward Prague.
After passing the Divišov area, the engine suddenly failed. Due to the nighttime conditions and the lack of available airfields in the immediate vicinity, the pilot declared an emergency and decided to perform an emergency landing on the D1 motorway. The pilot executed a 180-degree right turn and landed the aircraft on the motorway in the direction of Prague to Brno. Following the landing, the passengers assisted the pilot in pushing the undamaged aircraft to the shoulder of the road to avoid obstructing highway traffic.
There were no injuries to the crew or passengers, and the aircraft sustained no damage.
The investigation
The ÚZPLN investigation, conducted in cooperation with the Czech Police, examined the engine, fuel, and oil samples, as well as the mechanical integrity of the connecting rod. Technical examinations of the M-3 and AK engine revealed that the fuel and oil used were of the required quality. The investigation also scrutinized the aircraft's automatic fuel regulation system, which is designed to increase fuel flow during low oil pressure to prevent engine damage.
Findings
- The engine failure was caused by excessive sludge deposits within the cylinder #3 connecting rod cavities, which obstructed the oil flow to the bearing.
- This blockage led to the seizure of the bearing and the subsequent mechanical failure of the connecting rod head.
- The pilot's decision to continue the flight after observing the initial oil pressure drop was in violation of the aircraft's flight manual (Section 3.5).
- Testing did not confirm a failure in the automatic fuel regulation system's ability to respond to low oil pressure.