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 for dive test.
Comments sent must be received by April 8, 2002.
Send all comments on this proposed policy statement to the individual identified under FOR FURTHER INFORMATION CONTACT.Start Further Info
FOR FURTHER INFORMATION CONTACT:
Lowell Foster, FAA, Small Airplane Directorate, Regulations and Policy Branch, ACE-111, 901 Locust, Room 301, Kansas City, Missouri 64106; telephone (816) 329-4127; fax (816) 329-4090; email: <Lowell.Foster@faa.gov>.End Further Info End Preamble Start Supplemental Information
How Do I Comment on the Proposed Policy?
We invite your comments on this proposed policy statement PS-ACE100-2002-001. You may send whatever written data, views, or arguments you choose. We will consider all comments received by the closing date. We may change the proposals contained in this notice because of the comments received.
Please send comments to the individual identified under FOR FURTHER INFORMATION CONTACT. Comments sent using the Internet must contain “Comments to Policy Statement Number PS-ACE100-2002-001” in the subject line. Commenters should format in Microsoft Word 97 or ASCII any file attachments that are sent using the Internet.
Send comments using the following format:
—Organize comments issue-by-issue. For example, discuss a comment about the analysis and a comment about speed limits 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.
If sending your comments using the Internet will cause you extreme hardship, you may send comments using the U.S. Mail, overnight delivery, or facsimile machine. You should mark your comments, “Comments to Policy Statement PS-ACE100-2002-001” and send two copies to the above address in the section FOR FURTHER INFORMATION CONTACT.
What Would Be the General Effect of This Proposed Policy?
The FAA is presenting this information as a set of guidelines suitable for use. However, we do not intend for this proposed policy to become a binding norm; it does not form a new regulation, and the FAA would not apply or rely on it as a regulation. Start Printed Page 5356
The FAA Aircraft Certification Offices (ACO's) and Flight Standards District Offices (FSDO's) that certify changes in type design and approve alterations in normal, utility, and acrobatic category airplanes should try to follow this policy when appropriate. In addition, as with all advisory material, this statement of policy identifies one means, but not the only means, of compliance.
Because this proposed general statement of policy only announces what the FAA seeks to establish as policy, the FAA considers it an issue for which public comment is appropriate. Therefore, the FAA requests comments on the following proposed general statement of policy relevant to compliance with § 23.251 of the Federal Aviation Regulations (14 CFR 23.251), and other related regulations.
Section 23.251 must be addressed when approving replacement propellers. While flight testing to V-dive may not be required to show compliance for slow, low performance airplanes, it is normally necessary for higher-performance airplanes because they are more likely to inadvertently exceed their maximum speed.
We recently received a large number of supplemental type certification (STC) applications for replacement propeller installations on single engine airplanes with a reciprocating engine. The propellers are type certificated under 14 CFR part 21, § 21.29 (accepted under the bilateral agreement with the exporting country). The applicant questioned whether the airplanes modified with these propellers should be required to fly to dive speed under part 23, § 23.251 as part of the STC program in addition to showing compliance to § 23.33 for propeller overspeed.
Propeller overspeeds can occur during high-speed flight, such as the dive test. Overspeeding refers to a condition where the engine or propeller RPM limit is exceeded; typically because the airplane is going fast enough to drive the propeller (and engine) beyond the engine limits. The intent of § 23.33 is to ensure that propeller overspeeds did not occur within the normal flight envelope. This intent differs from that in the V-Dive requirements, § 23.251, which were intended to address airframe vibration and buffeting. The intent of these requirements are supported by the Flight Test Report Guides for both CAR 3 and early part 23 (FAA Form 8110-11 and 8110-18) which had an allowance for the use of a different propeller for the dive test if the production propeller would overspeed the engine beyond that allowed by the engine manufacturer. This practice of allowing different propellers supports that the original intent of § 23.251 was not an engine/propeller control test, but an airframe test addressing vibration and buffeting.
Service history for light, low-speed (typically 2-4 place) reciprocating engine powered airplanes has validated the testing limits used for both the § 23.33 and § 23.251 requirements. This airplane class is typically slow enough that it is unlikely the pilot would inadvertently exceed VNE. Furthermore, in most cases, at dive speed, the air is driving the propeller and there are not any pressure pulses from the propeller to affect the airframe. The other concern is the propeller overspeeding the engine. Finally, the frequency of the propeller and engine RPM are typically far from any airframe harmonic frequency.
Propellers on multiengine and turboprop airplane installations are more critical than on light, low-speed airplanes and applicants should consider including a dive test for these certification programs. Previous dive tests on a turbine powered, multiengine airplane uncovered a problem with the engine/propeller control system. While § 23.251 is not intended to address propeller or engine control problems directly, this problem was severe enough to warrant a design change because of safety considerations. In addition, It is typically easier and therefore more likely that the pilot of a larger, multiengine airplane or turbine powered airplane will inadvertently exceed VNE or VMO in normal operation. Additionally, there have been propeller/turbine engine runaways caused by over-speeding during the V-dive test. Performing the V-dive test for the propeller installation program would insure that a propeller/engine problem is not discovered inadvertently during follow-on non-propulsion based airplane modifications requiring test pilots to demonstrate the airplane out to V-dive.
Part 23, § 23.251 requires that the aircraft be free of vibration and buffeting that could interfere with the pilot's ability to safely fly the aircraft, at all speeds up to VD, in all approved airplane configurations. Compliance with § 23.251 is typically shown with a flight demonstrating that all design analysis and margins related to airframe vibration and buffeting, including those established for the propeller/engine/airframe, are adequate to provide a safe airplane up to its dive speed.
Section 23.251 must be addressed when approving replacement propellers. While dive testing the airplane is one way to demonstrate compliance to § 23.251, it may not be necessary for light, low-speed airplanes that are unlikely to inadvertently exceed the maximum speed of the airplane. Conversely, dive testing should be performed for higher-performance airplanes because they are more likely to inadvertently exceed their maximum speed.
For light, low-speed airplanes, should the applicant choose not to perform a dive test, then other means of compliance acceptable to the FAA must be provided. One way of addressing § 23.251 is for an applicant to provide evidence of positive service history or that the new propeller/engine combination has been tested on a previous program to the same or a higher speed being requested. Applicants have also shown compliance with § 23.251 by analysis and by limiting VD to a lower value such as VNE. VNE now becomes the new VD, and a new VNE is established at a lower speed.Start Signature
Issued in Kansas City, Missouri, on January 29, 2002.
Marvin R. Nuss,
Acting Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. 02-2720 Filed 2-4-02; 8:45 am]
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