What happened
On February 20, 2021, a Boeing 747-412BCF operated by Longtail Aviation was performing a scheduled cargo takeoff from Runway 21 at Maastricht Aachen Airport. During the initial climb phase, the aircraft experienced a failure in engine number one. The failure was uncontained, causing components of the engine to exit the tailpipe. These fragments traveled approximately 2 kilometers south of the runway end, landing in the village of Meerssen. The impact of the debris caused damage to houses and vehicles, and two persons on the ground sustained injuries. Following the failure, the flight crew shut down the affected engine and diverted to Liege Airport in Belgium, where they landed safely.
The investigation
The Dutch Safety Board (OVV) investigated the incident to determine the cause of the engine failure and to evaluate the risks posed to residents living near the airport. The investigation focused on the mechanical integrity of the high-pressure turbine and the maintenance history of the engine. Investigators examined the physical condition of the engine parts, metallurgical analysis of the turbine components, and the compliance records of various Service Bulletins and Airworthiness Direct and Directives. The inquiry also addressed the lack of documentation regarding the decision-making process for certain engine modifications during previous ownership transitions.
Findings
Technical analysis revealed that the failure originated in the high-pressure turbine of the first engine. The investigation established that prolonged exposure to high gas temperatures caused the outer transition duct panels to undergo wear and deformation. Specifically, one panel fractured and another became loose, leading to severe internal damage that allowed debris to be ejected from the engine.
Crucially, while the engine had been updated with new transition duct panels, it had not been equipped with the additional cooling features recommended in Service Bulletin 72-462. The absence of these cooling features allowed gas temperatures to reach levels exceeding 2,000 °F, which was significantly higher than the typical operating range. The investigation found that the installation of these cooling features was not mandatory, and the operator could not provide documented reasoning for why the modification had not been implemented.