What happened
On 15 September 2012, an Aero Vodochody L-39C Albatros, registration ES-YLS, was part of a seven-aircraft formation flight following a display at Den Helder Airport. While cruising at approximately 3,500 feet near Valkenswaard, the crew—consisting of a pilot and a mechanic—experienced intense engine vibrations and a burning odor.
Shortly after, a general fault warning was triggered, accompanied by a drop in oil pressure. The crew witnessed an explosion and observed flames exiting the aircraft's exhaust. After the pilot shut off the fuel supply and activated the fire extinguisher, the engine lost power. Realizing the aircraft could not reach a safe landing site, the pilot steered the jet toward an open area. At an altitude of roughly 1,500 feet, the mechanic ejected, followed by the pilot. The aircraft subsequently crashed into a potato field and was destroyed. Both occupants survived the incident without injury.
The investigation
The Dutch Safety Board (OVV) conducted a technical examination of the Ivchenko AI-2-25TL engine. The investigation involved the disassembly of the engine in the Czech Republic and metallurgical analysis by the National Aerospace Laboratory (NLR).
Investigators examined the condition of the turbine blades, which showed severe burning from high exhaust gas temperatures. Further analysis focused on the internal components located between the low-pressure compressor and the low-pressure turbine. The investigation also reviewed maintenance records and laboratory oil analyses performed prior to the accident.
Findings
Technical analysis identified the defective low pressure turbine front bearing as the root cause of the engine failure. The investigation established that cracks in the bearing's inner ring and the presence of wear particles in the oil indicated a progressive degradation process. This bearing failure created excessive stress on a coupling bolt, causing it to break. The failure of this bolt led to the twisting and eventual fracture of the engine's oil tube.
Additionally, the investigation found that a laboratory assessment of the engine oil quality had been conducted without any written reference standards. It was also noted that the L-39C aircraft type is not required to meet certain European safety level requirements.