# 14 CFR § 27.547: Main rotor structure

> Federal · Regulations · In force

URL: https://www.frixlaw.com/law-library/statutes/ecfr-14-27.547

## Section

- **Citation:** 14 CFR § 27.547
- **Heading:** Main rotor structure
- **Jurisdiction:** Federal
- **Kind:** Regulations
- **Status:** In force
- **Text as of:** September 22, 2026
- **Source:** Publisher's official text
- **Location:** Title 14—Aeronautics and Space > CHAPTER I—FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION > SUBCHAPTER C—AIRCRAFT > PART 27—AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT > Subpart C—Strength Requirements > Main Component Requirements

## Text

(a) Each main rotor assembly (including rotor hubs and blades) must be designed as prescribed in this section.
(b) [Reserved]
(c) The main rotor structure must be designed to withstand the following loads prescribed in §§ 27.337 through 27.341:
(1) Critical flight loads.
(2) Limit loads occurring under normal conditions of autorotation. For this condition, the rotor r.p.m. must be selected to include the effects of altitude.
(d) The main rotor structure must be designed to withstand loads simulating—
(1) For the rotor blades, hubs, and flapping hinges, the impact force of each blade against its stop during ground operation; and
(2) Any other critical condition expected in normal operation.
(e) The main rotor structure must be designed to withstand the limit torque at any rotational speed, including zero. In addition:
(1) The limit torque need not be greater than the torque defined by a torque limiting device (where provided), and may not be less than the greater of—
(i) The maximum torque likely to be transmitted to the rotor structure in either direction; and
(ii) The limit engine torque specified in § 27.361.
(2) The limit torque must be distributed to the rotor blades in a rational manner.
(Secs. 604, 605, 72 Stat. 778, 49 U.S.C. 1424, 1425)
[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as amended by Amdt. 27-3, 33 FR 14105, Sept. 18, 1968]

## Nearby sections

- [14 CFR § 27.301 § 27.301 Loads.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.301.md)
- [14 CFR § 27.303 § 27.303 Factor of safety.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.303.md)
- [14 CFR § 27.305 § 27.305 Strength and deformation.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.305.md)
- [14 CFR § 27.307 § 27.307 Proof of structure.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.307.md)
- [14 CFR § 27.309 § 27.309 Design limitations.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.309.md)
- [14 CFR § 27.321 § 27.321 General.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.321.md)
- [14 CFR § 27.337 § 27.337 Limit maneuvering load factor.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.337.md)
- [14 CFR § 27.339 § 27.339 Resultant limit maneuvering loads.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.339.md)
- [14 CFR § 27.341 § 27.341 Gust loads.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.341.md)
- [14 CFR § 27.351 § 27.351 Yawing conditions.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.351.md)
- [14 CFR § 27.361 § 27.361 Engine torque.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.361.md)
- [14 CFR § 27.391 § 27.391 General.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.391.md)
- [14 CFR § 27.395 § 27.395 Control system.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.395.md)
- [14 CFR § 27.397 § 27.397 Limit pilot forces and torques.](https://www.frixlaw.com/law-library/statutes/ecfr-14-27.397.md)

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Source: Frix Law Library, https://www.frixlaw.com/law-library/statutes/ecfr-14-27.547. Check the current official text before relying on it. Not legal advice.