Awakened by a noise like a blast, you look out the cabin and find some pipes and wires reveal outside the airplane engine, and it looks like part of the engine is gone. What happened? The airplane engine that people usually see in fact is the engine cowl called nacelle that includes Inlet, Fan Cowl, Thruster Reverser and Nozzle. Normally the parts gone are the fan cowls, which can open on the ground for airplane engine maintenance. If the fan cowls didn’t lock completely after closing, the strong airflow may tear off the fan cowls in flight.
So will this kind of engine part loss cause a crash? In aviation design, engineers classify the different areas of an airplane into the primary and secondary structures. The primary structure is defined as the one that can directly affect flight safety, however, the loss or failure of the secondary structure will not lead to a direct safety issue. Fortunately, the fan cowl belongs to the secondary structure, and the engineers have taken into account such a situation.