Windmilling: Extending a Dutch Tradition

For more than a decade, IGB has been involved in Airbus projects examining the impact of SEI on interiors and GAINS.

Sustained Engine Imbalance (SEI) or “Windmilling” as it is known in the aircraft industry, describes an imbalance in aero-engines due to partial or complete loss of an engine fan blade or shaft support failure in flight. After the engine spool down, air in-flow will rotate the fan creating large out-of-balance forces that provide a source of excitation (vibrations) for the whole engine-wing-aircraft structure.*

So in 2000, the FAA and then JAA (presently EASA) required SEI compliancy. And with their introduction of the A340-500/-600 series, Airbus was the first manufacturer to fulfill this demanding / challenging requirement. Since then, the significance of windmilling did not go unrecognized by Airbus. Presently Airbus requires SEI certification for A318, A320NEO, A350 and A380 series.

The ramifications for OEMs are great. In fact, all aircraft interior parts such as galleys, stowages and crew rests must comply with this requirement.

IGB has been involved with the SEI certification of interior parts from the moment that these requirements became effective. For more than a decade we have realized several projects in close contact with Airbus and acquired extensive experience in the certification of aircraft interior units for the A318, A320NEO, A340, A350 and A380.

Finite Element Analysis (FEA) is used for both the strength of the unit and the fatigue requirements (endurance of metallic parts).

Our experience with the analytical approach by means of random response and Frequency Response Analysis (FRA) has been backed up with experience with vibration testing at several test houses and with several types of monuments and GAINS.

*The windmilling requirements are resulting from FAA Issue Paper (IP) A-616, and JAA Certification Review Item (CRI) P-1018 (based on FAA Advisory Circular 25-24).

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