14 C.F.R. § 29.481 Tail-down landing conditions.
Title 14 - Aeronautics and Space
(a) The rotorcraft is assumed to be in the maximum nose-up attitude allowing ground clearance by each part of the rotorcraft. (b) In this attitude, ground loads are assumed to act perpendicular to the ground.
Title 14: Aeronautics and Space
PART 29—AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY ROTORCRAFT
Subpart C—Strength Requirements
Ground Loads
§ 29.481 Tail-down landing conditions.