On Saturday 20 February 2021, a Boeing 747-400 encountered a contained engine failure during the initial climb. The engine failure caused parts of the engine to exit the tail pipe of the engine and to come down in the village of Meerssen. The engine parts injured two people and damaged property such as houses and cars. After the flight crew had shut down the engine, they diverted to Liege Airport in Belgium, where a safe landing was made.
Risk assessment of parts departing the aircraft necessary
This engine failure and subsequent departing engine debris was due to a failure of the turbine of the number one engine. Elevated gas temperatures that existed for an extended period of time in the turbine of the engine were causing wear and deformation of outer transition duct panels. This resulted in one outer transition duct panel coming loose and one being fractured, which subsequently caused severe damage to the turbine. Consequently, engine debris exited the tail pipe of the engine and came down in the village of Meerssen.
Risk management by an adequate record keeping
The manufacturer of the engine was aware of the problem with the outer transition ducts coming loose since the nineteen-eighties. To prevent the failure of the outer transition ducts and turbine section, several service bulletins were issued since 1993. The investigation revealed that the engine was equipped with new outer transition duct panels; however, the engine was not modified with the additional cooling features. Those cooling features were supposed to prevent a too high level of gas temperature. The installation of these cooling features, as advised by a service bulletin, was not mandatory. The operator was not able to present the documented reasoning regarding the non-incorporation of this service bulletin. Having an adequate record keeping of maintenance documentation enables the operator and its maintenance organisation to make sound risk management decisions about the continuing airworthiness of their aeroplanes. This is crucial for the safe operation throughout the operating life of, in this case, the engine.
Residents around airports are at least exposed to two types of risks: first, parts departing the aircraft, and second an accident with an aircraft. Until now, an assessment for residential areas around Maastricht Aachen Airport of the risks of parts departing the aircraft, such as departing engine debris, has not routinely been done. According to the Dutch Safety Board, based on the results of such an assessment an informed decision about the acceptability of these local risks should be made.
The Dutch Safety Board issues the following recommendations:
To Longtail Aviation:
1. Make and keep the record keeping of the (non-)implementation of service bulletins for leased engines of your fleet of commercial air transport aeroplanes complete and accessible.
To United States Federal Aviation Administration:
2. Reconsider whether Service Bulletin 72-462, in light of third party risk, should be made mandatory through an Airworthiness Directive.
To the Minister of Infrastructure and Water Management:
3. Perform and publish an assessment for residential areas around Maastricht Aachen Airport of the risks of parts departing the aircraft, such as departing engine debris.
Parties intend to follow Dutch Safety Board recommendations
Risico-inschatting van vallende vliegtuigonderdelen noodzakelijk
Interim statement ‘Engine failure, Boeing 747-412BCF, Meerssen'