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Interim Guidelines for Certification and Continued Airworthiness of Unbalanced Control Surfaces With Freeplay and Other Nonlinear Features

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Information about this document as published in the Federal Register.

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Federal Aviation Administration (FAA), DOT.


Notice of proposed interim guidelines; request for comments.


The Federal Aviation Administration (FAA) announces the availability of proposed Interim Guidelines for Certification and Continued Airworthiness of Unbalanced Control Surfaces with Freeplay and Other Nonlinear Features.


Send your comments on or before May 25, 2006.


Address your comments to the individual identified under FOR FURTHER INFORMATION CONTACT.

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Gerald Lakin, Federal Aviation Administration, Transport Airplane Directorate, Transport Standards Staff, Standardization Branch, ANM-113, 1601 Lind Avenue, SW., Renton, WA 98055-4056; telephone (425) 227-1187; fax (425) 227-1320; e-mail:

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Comments Invited

The proposed memorandum is available on the Internet at the following addresses:​rgl, and​aircraft/​draft_​docs. If you do not have access to the Internet, you can obtain a copy of the proposed memorandum by contacting the person listed under FOR FURTHER INFORMATION CONTACT.

The FAA invites your comments on this proposed memorandum. We will accept your comments, data, views, or arguments by letter, fax, or e-mail. Send your comments to the person indicated in FOR FURTHER INFORMATION CONTACT. Mark your comments, “Comments to Policy Statement No. ANM-05-115-019.”

Use the following format when preparing your comments:

  • Organize your comments issue-by-issue.
  • For each issue, state what specific change you are requesting to the proposed interim guidelines.
  • Include justification, reasons, or data for each change you are requesting.

We also welcome comments in support of the proposed interim guidelines.

We will consider all communications received on or before the closing date for comments. We may change the proposed interim guidelines because of the comments received.


This memorandum clarifies FAA guidance on the design, certification, and continued airworthiness of control surfaces that rely on retention of restraint stiffness for flutter prevention. These control surfaces typically do not have added mass balance, but there are some that are partially mass balanced for which the guidelines would also apply. This memorandum provides acceptable means of establishing and certifying freeplay limits and inspection procedures, provides guidance for managing freeplay over the airplane service life, and provides a means of finding compliance for control system designs whose failure can result in a nonlinear aeroelastic configuration and limit cycle oscillation (LCO). This memorandum provides interim guidelines and standardized methods of compliance that address the inadequacies of current guidance, until the FAA revises the applicable guidance contained in AC 25.629-1A.

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Issued in Renton, Washington, on April 9, 2006.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification Service.

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[FR Doc. 06-3858 Filed 4-21-06; 8:45 am]