What is a primary effect of high density altitude on helicopter performance?

High density altitude significantly affects helicopter performance, with one of the most primary effects being reduced engine power. As density altitude increases, the air becomes less dense, which directly impacts the engine's ability to generate power. In thin air, the engine cannot intake as much oxygen, leading to a drop in performance. This reduction in power means that the helicopter may struggle to achieve the necessary lift, resulting in a longer takeoff distance and reduced climb rate. Furthermore, under high density altitude conditions, helicopters may not be able to carry as much weight, and maneuverability can be compromised, affecting overall flight safety and efficiency.

The other options related to visibility, takeoff distance requirements, and rotor efficiency do not align with the impairments caused by high density altitude. In fact, visibility may not be directly affected by density altitude, and takeoff distances typically increase under these conditions rather than decrease, making those aspects less relevant to the question. Similarly, rotor efficiency tends to decrease as well, rather than improve, when density altitude is high. Understanding these dynamics is crucial for pilots to ensure safe operation in challenging conditions.