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Proposed Issuance of Policy Memorandum, In-Flight Operation of Propellers at Pitch Settings Below the Flight Regime for Part 23/CAR 3 Airplanes

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Information about this document as published in the Federal Register.

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Federal Aviation Administration, DOT.


Notice of policy statement; request for comments.


This document proposes to adopt new policy for certification of normal, utility, acrobatic, and commuter category turbine powered airplanes with propeller beta mode pitch settings.


Comments submitted must be received no later than October 2, 2000.


Send all comments on this proposed policy statement to the individual identified under FOR FURTHER INFORMATION CONTACT.

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Randy Griffith, Federal Aviation Administration, Small Airplane Directorate, Regulations and Policy Branch, ACE-111, 901 Locust, Room 301, Kansas City, Missouri 64106; telephone (816) 329-4126; fax (816) 329-4090; email: <>.

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Comments Invited

We invite your comments on this proposed policy statement, ACE-00-23.1155-01. You may submit whatever written data, views, or arguments you choose. You should mark your comments, “Comments to policy statement ACE-00-23.1155-01” and submit in duplicate to the above address. We will consider all comments received on or before the closing date. We may change the proposals contained in this notice in light of the comments received.

You may also send comments via the Internet using the following address: Comments sent via fax or the Internet must contain “Comments to policy statement ACE-00-23.1155-01” in the subject line. You do not need to submit in duplicate. Writers should format in Microsoft Word 97 or ASCII any file attachments that are sent via the Internet.

Submit comments using the following format:

  • Organize comments issue-by-issue. For example, discuss a comment concerning design evaluation and a comment about maintenance as two separate issues.
  • For each issue, state what specific change you are requesting to the proposed policy memorandum.
  • Include justification (for example, reasons or data) for each request.

The Proposed Policy


The National Transportation Safety Board (NTSB) has recommended rulemaking action to amend 14 CFR part 23 to require a means to prevent in-flight operation of the propeller at pitch settings below the flight regime (beta mode). For turbine engine installations, Amendment 23-7, § 23.1155, requires that operation of the propeller controls for pitch settings below the flight regime have a means to prevent inadvertent operation. The new requirement recommended by the NTSB would be fundamentally different from the current § 23.1155. Unless the airplane is certificated for such use, beta mode could not occur in-flight, even if intentionally commanded. The Small Airplane Directorate is initiating an ARAC, Aviation Rulemaking Advisory Committee, study to determine whether a rulemaking effort should occur.

The FAA has taken actions to address previously certificated airplanes with in-flight beta capability. A fleet wide review of all turbopropeller powered transport, normal, utility, acrobatic, and commuter category airplanes was performed. As a result of the review, FAA issued Airworthiness Directives that required applicable Flight Manuals to include an operational limitation with consequence statement for in-flight beta operation.

Additionally, the safety of future type certificated airplanes, with in-flight beta capability, or currently certificated airplanes, which are being modified to add an in-flight beta capability, should be assessed. This assessment should consider both inadvertent and intentional operation of propellers in pitch settings below the flight regime.

Inadvertent In-Flight Operation

Regarding inadvertent operation, as previously mentioned, Amendment 23-7 added a requirement (§ 23.1155) that operations of the propeller controls at pitch settings below the flight regime have a means to prevent inadvertent operation. For airplanes with a certification basis before Amendment 23-7 that are modified to add in-flight beta capability, the provisions of 14 CFR part 21, § 21.101(b) should be used to evaluate the possible unsafe nature of inadvertent operation of propellers in the beta regime. If it is determined that such operation is unsafe, the issue may be addressed by showing compliance with § 23.1155 at Amendment 23-7 or subsequent.

The nature of the regulatory requirement provided by § 23.1155 allows a subjective, qualitative evaluation for compliance determination. The intent is to prevent inadvertent operation in the beta mode, even if the possibility of inadvertent operation is remote. If an operation or feature of the design can allow in-flight, inadvertent placement of the control below the flight regime, the design does not comply with the regulation. In other words, the design should be evaluated considering the types of operations that will be seen in service. Consider items such as hardware wear modes or maintenance issues that may cause the control to be inadvertently placed or creep into the beta regime over a period of time.

Intentional In-Flight Operation

On all future type certification projects, the Flight Manuals should include the appropriate operational limitations and consequence statement for in-flight beta operation.

Beta Lock-Out Systems

To add a level of assurance that in-flight beta will not occur, some airplanes have incorporated lock-out systems. These systems eliminate the ability to perform this operation in flight, even if intentionally commanded. It is important to note that the installation of a beta lock-out system can not be used in lieu of the design requirements of § 23.1155 compliance. Also, in some cases, propeller beta operation is used to show compliance with stopping distances in 14 CFR part 23, Subpart B. In accordance with Subpart B, when means other than wheel brakes are used for determining Start Printed Page 53341stopping distances, the means must be “safe and reliable.” If beta operation is used to show compliance with stopping distances, the reliability of a system that would prevent in-flight beta operation must be such that this capability, when required, will be available to comply with 14 CFR part 23, Subpart B, and 14 CFR part 21, § 21.21(b)(2) or § 21.101(b). With a systems safety analysis, you can determine the required reliability level for the beta lock-out system based on the hazard level (for example, § 23.1309 compliance).

You should perform a systems safety analysis on airplanes with beta lock-out systems. This analysis will consider hazards such as the inability to command beta on one engine on a multiengine airplane. For example, If you command beta on both 2 engines during land roll-out, but only one propeller goes into beta mode, this might adversely affect ground controllability.

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Issued in Kansas City, Missouri on August 16, 2000.

Michael Gallagher,

Manager, Small Airplane Directorate, Aircraft Certification Service.

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[FR Doc. 00-22540 Filed 8-31-00; 8:45 am]