What happened
On April 20, 2012, a Zlín Z 226T, registration OK-MGF, was performing a flight from Tábor to Jihlava. The aircraft was occupied by a pilot and one passenger, both of whom were qualified aviators. The flight proceeded normally after takeoff until the aircraft reached an altitude of approximately 300 meters AGL.
Approximately ten minutes into the flight, while operating near the site of the former Kámen airfield, the pilot experienced a heavy impact from the engine area, followed by an immediate loss of engine power and an oil leak. The pilot promptly decided to perform an emergency landing, selecting a landing area at the former Ká andmen airfield which was within sight. The pilot executed a 180-degree turn toward the runway and shut down the engine approximately one kilometer before reaching the strip. The aircraft landed safely on the paved surface without further damage to the airframe. There were no injuries to the two crew members.
The investigation
The ÚZPLN investigation focused on the technical inspection of the WM-6-III engine and the aircraft's maintenance records. The inspection of the engine revealed significant internal damage. Specifically, the right side of the engine mount was damaged, and the engine block was pierced on both sides at the location of cylinder number 2.
Investigators found that a portion of the connecting rod eye from cylinder 2 had become wedged in the puncture. Upon removing the engine cover, metal fragments from piston rings and the connecting rod were discovered within the engine interior. The eye of the connecting rod attached to the crankshaft had fractured, and a portion of the bolt and nut used to secure the rod eye was found lodged in the oil return line. The engine's exterior, including the cowlings and cockpit glazing, was coated in an oil film.
Findings
- The primary cause of the serious incident was an engine failure caused by the fracture of the connecting rod eye in cylinder 2.
- The failure was most likely due to operational wear and the development of a hidden material defect caused by fatigue.
- The engine, which had been in service since 1958, had been subjected to high operational loads, primarily through glider towing duties.
- The secondary damage to the engine components was a direct result of the fractured rod and the subsequent period of engine operation at reduced power.
- The pilot and the aircraft were both fully qualified and airworthy at the time of the event.
Safety action
As a result of this incident, the ÚZPLN issued a general safety recommendation advising all operators of aging aircraft to ensure meticulous care and maintenance in strict accordance with operational and maintenance manuals.