[Federal Register Volume 67, Number 24 (Tuesday, February 5, 2002)]
[Notices]
[Pages 5355-5356]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-2720]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

[Policy Statement Number PS-ACE100-2002-001]


Proposed Issuance of Policy Memorandum, Dive Test for Part 23/CAR 
3 Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of policy statement; request for comments.

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SUMMARY: This document proposes to adopt new policy for certification 
of normal, utility, acrobatic, and commuter category turbine powered 
airplanes for dive test.

DATES: Comments sent must be received by April 8, 2002.

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

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: [email protected]>.

SUPPLEMENTARY INFORMATION:

Comments Invited

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.

[[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 Sec. 23.251 of the Federal Aviation 
Regulations (14 CFR 23.251), and other related regulations.

Summary

    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.

Background

    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, Sec. 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, 
Sec. 23.251 as part of the STC program in addition to showing 
compliance to Sec. 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 Sec. 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, Sec. 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 Sec. 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 Sec. 23.33 and Sec. 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 
Sec. 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.

Policy

    Part 23, Sec. 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 Sec. 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 Sec. 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 Sec. 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 Sec. 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.

    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]
BILLING CODE 4910-13-P