What two conditions must be met for a spin to occur?

A spin occurs when an aircraft is in an incipient spin condition, which is characterized by the combination of a stall and a yawing motion. When the aircraft stalls, one wing may lose lift before the other, causing an imbalance in forces. This imbalance leads to a yawing motion, usually towards the wing that is producing more lift and less drag.

For a spin to take place, it is essential that the aircraft is stalled because, in this state, the control surfaces and aerodynamic performance are significantly compromised, meaning that traditional recovery techniques may not be effective. The yawing action exacerbates the imbalance, leading to a spiraling descent known as a spin. Thus, both a stall and a yaw must occur simultaneously for a spin to initiate and proceed.

The other choices do not address both critical elements needed for a spin. For example, stall and roll might refer to losing control but do not necessarily account for the yaw component that is essential for a spin. Similarly, yaw and turbulence, while they can disrupt flight stability, do not inherently lead to a spin without the stall condition being present. Lastly, weight and drag are important aerodynamic factors but do not directly describe the dynamics that lead to a spin.