Helicopter Landing Zone Size, Slope, and Approach

The size check is a clear square keyed to rotor diameter -- roughly twice the rotor for a routine daytime landing, and larger at night, in dust or snow, or with a sling load. The slope check is the aircraft's own published limit, usually somewhere under ten degrees and often less across the roll axis than the pitch axis, and it is what disqualifies most hillside clearings. The approach check is the one a ground team miscalculates. The aircraft does not want to descend vertically into a hole; it wants a shallow approach and departure into the wind, commonly ten to one or shallower, and that path has to clear every obstacle. A 40 ft tree line on the approach end does not cost forty feet of clearing, it costs four hundred feet of clear approach beyond it, and doubling the tree height doubles that requirement -- the approach is linear in obstacle height and unforgiving. That is why a clearing that measures fine on the ground is refused from the air: a 50 ft rotor aircraft needs a 100 ft square and can accept six degrees of slope against an eight degree limit, and still fails if a second tree line stands 300 ft out. A screening aid, never a clearance: the aircrew, the aircraft's published limits, and the pilot in command decide whether a site is usable.

required_side_ft = size_factor x rotor_diameter_ft; slope_limit_pct = tan(slope_limit_deg) x 100; approach_length_ft = obstacle_height_ft x approach_ratio; total_clear_ft = required_side_ft + 2 x approach_length_ft.

Helicopter landing zone screening on three checks -- a clear square keyed to rotor diameter, the aircraft's published slope limit, and an approach path at the stated ratio clearing the tallest obstacle -- by name; the size factor, slope limit, and approach ratio are entered rather than bundled because they belong to the aircraft and the conditions. A screening aid, never a clearance: the aircrew and the pilot in command decide.

The three checks are geometry on values the crew measures and the aircrew publishes; no aircraft's limits are reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: rotor_diameter_ft, size_factor, measured_clear_ft, ground_slope_deg, slope_limit_deg, obstacle_height_ft, approach_ratio, required_side_ft, slope_limit_pct, approach_length_ft, total_clear_ft

• Size factor about 2x rotor diameter for routine daytime; larger at night, in dust or snow, or with a sling loadhelicopter LZ practice
• Slope limit the aircraft's published figure, often tighter across roll than pitchaircraft flight manual
• Approach linear in obstacle height at the approach ratio; a 10:1 path over a 40 ft obstacle needs 400 ft beyond ithelicopter LZ practice