Mechanical turbulence is produced when wind encounters a physical obstacle like a tree, hill, or another aircraft. The obstacle disrupts the smooth flow, creating gusts, eddies, and irregular air movement. This disturbance starts where the air first meets the obstacle and can be felt upwind as the flow is forced to rise, bend, and mix. That’s why you’re likely to encounter these turbulent, chaotic air pockets near the windward side of such obstacles. The other options don’t describe a phenomenon tied to how airflow is disturbed by obstacles in the same way: they refer to conditions or effects that aren’t specifically about the turbulence generated by obstruction.

In a prolonged spiral turn, the speed you gain mainly comes from the bank angle you hold. A steeper bank makes the turn tighter and increases the turn rate. That tighter turn means you descend more quickly because the lift is tilted more toward turning than supporting vertical weight, so gravity pulls you down faster along the curved path. As you lose altitude while turning, that potential energy converts into kinetic energy, raising your airspeed along the flight path. So the steeper the bank during turns, the more the airspeed tends to build in a sustained spiral. That’s why the option describing a steep bank angle during turns is the best answer. The other choices don’t describe the mechanism that drives speed up in a prolonged spiral: unexpected sink refers to vertical speed, not the forward speed gained from a spiral; flying a certified canopy isn’t about speed dynamics in spirals; and deep input on the glider isn’t the standard factor responsible for accelerating in a sustained spiral.

When you’re close to terrain and about to do a full circling 360, use figure eight turns to maintain terrain clearance. This pattern combines two lobes that loop in opposite directions, letting you stay in safer, more controllable air on both sides of the obstacle. It gives you a chance to check wind direction, rotor, and lift while keeping a comfortable distance from the terrain, and it creates an easy exit toward open space before committing to the larger circle. This setup reduces the risk of being drawn into terrain if the wind shifts or turbulence increases. The other maneuvers either drop you more aggressively or don’t provide the same controlled setup: a full stall is risky near obstacles, a spiral dive is a steep descent that can push you toward terrain, and S-turns don’t offer the same reliable path to safely reorient and clear the terrain before a big turn.

When you fly near terrain, the air flow around the hill and the wind you’re flying in can be unpredictable, creating a strong wind gradient and possible rotor effects. A steep turn changes your direction quickly, but your ground track doesn’t just follow your nose—it rides the wind. If the wind is pushing you toward the hill, that drift can move you into the slope even while you’re banking to turn away. With limited altitude margin close to terrain, this wind-driven drift reduces your clearance and makes it easy to hit the hill. So, the main danger here is being carried downwind into the terrain during a steep turn. Keeping a safe distance from the hill, using moderate bank angles, and maintaining awareness of wind direction and terrain effects helps prevent this drift. The other factors—extreme bank angles, strong inputs, or sudden sink—are risks in general, but they’re not the specific, immediate threat created by performing steep turns near terrain.