14 CFR § 29.75

For each rotorcraft—

The corrected landing data must be determined for a smooth, dry, hard, and level surface;

The approach and landing must not require exceptional piloting skill or exceptionally favorable conditions; and

The landing must be made without excessive vertical acceleration or tendency to bounce, nose over, ground loop, porpoise, or water loop.

The landing data required by §§ 29.77, 29.79, 29.81, 29.83, and 29.85 must be determined—

At each weight, altitude, and temperature for which landing data are approved;

With each operating engine within approved operating limitations; and

With the most unfavorable center of gravity.