What limitation is crucial when planning large scale helicopter operations?

Good visibility and illumination is crucial when planning large-scale helicopter operations because these factors directly impact safety, navigation, and operational effectiveness. In aviation, visibility determines the ability of pilots to see the terrain, other aircraft, and any potential hazards during flight or landing. Poor visibility can complicate flight maneuvers, increase the risk of accidents, and hamper mission success.

Illumination is particularly important during night operations or in low-light conditions, as it affects pilots' visual acuity and situational awareness. Adequate lighting ensures that pilots can effectively assess their surroundings, perform landings, and conduct air-to-ground tasks safely. Both visibility and illumination are essential for ensuring the safety of crew and equipment during complex operations where precision is key.

Operational cost, while a significant factor in planning, does not directly relate to the immediate operational capability or safety during the flight. Increased range is desirable for extending operational capacity but is not a limitation tied to planning processes. Additionally, while reduced personnel capacity affects operational capability, it is not as critical to the immediate conditions of visibility and safety like illumination is.