What is considered a primary structure in aircraft?

In the context of aircraft, the term "primary structure" refers to essential components that contribute significantly to the aircraft's structural integrity and safety during flight. This includes components like engine mounts and wing spars, which are critical for bearing loads and ensuring the aircraft can withstand the forces experienced during operation.

These primary structures are designed to carry the weight and stresses associated with flight operations, making them fundamentally important for the aircraft's functionality. They are engineered to provide strength and stability, which are necessary for maintaining the aircraft's performance and safety standards.

In contrast, components designed for low-stress applications or primarily for aesthetic appeal do not contribute directly to the safety or performance of the aircraft. Similarly, lightweight materials that serve purely decorative purposes do not play a role in the structural integrity of the aircraft. Therefore, the significance of primary structures lies in their critical function, ensuring that the aircraft can operate safely and effectively under various conditions.