[Federal Register Volume 66, Number 47 (Friday, March 9, 2001)]
[Notices]
[Pages 14243-14245]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-5603]


-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

[Policy Statement Number ACE-00-23.683-01A]


Proposed Issuance of Policy Memorandum, Discussion of Compliance 
Methods in Advisory Circular (AC) 23-17, Systems and Equipment Guide 
for Certification of Part 23 Airplanes, Paragraph 23. 683, Operation 
Tests

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of policy statement; request for comments.

-----------------------------------------------------------------------

SUMMARY: This document announces a Federal Aviation Administration 
(FAA) proposed general statement of policy applicable to the type 
certification of normal, utility, acrobatic, and commuter category 
airplanes. This document advises the public, in particular 
manufacturers of normal, utility, acrobatic, and commuter category 
airplanes, of more information related to the compliance methods in 
Advisory Circular (AC) 23-17, Systems and Equipment Guide for 
Certification of Part 23 Airplanes, Paragraph 23.683, Operation Tests. 
This notice is to tell the public about proposed FAA policy and give 
all interested people an opportunity to present their views on the 
proposed policy statement.

DATES: Comments sent must be received by April 9, 2001.

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

FOR FURTHER INFORMATION CONTACT:   
--Comments. Pat Nininger, FAA, Small Airplane Directorate, ACE-111, 
Room 301, 901 Locust, Kansas City, Missouri 64106; telephone (816) 329-
4129; fax 816-329-4090; e-mail Pat. [email protected]>.
--Technical. Lester Cheng, FAA, Small Airplane Directorate, ACE-111, 
Room 301, 901 Locust, Kansas City, Missouri 64106; telephone (816) 329-
4120; fax 816-329-4090; e-mail: [email protected]>

SUPPLEMENTARY INFORMATION:

Comments Invited

How Do I Comment on This Proposed Policy?

    We invite your comments on this proposed policy statement. Send 
written data, views, or arguments. Mark your comments, ``Comments to 
policy statement ACE-00-23.683-01A,'' and send two copies to the above 
address. We will consider all comments received by the closing date. We 
may change the proposals contained in this notice because of the 
comments received.
    You may also send comments using the Internet to the following 
address: Pat. [email protected]>. Comments sent by fax or the Internet 
must contain, ``Comments to policy statement ACE-00-23.683-01A'' in the 
subject line. You do not need to send two copies. Writers should format 
in Microsoft Word 97 or ASCII any file attachments that are sent by the 
Internet.
    Send comments using the following format:

--Organize comments issue-by-issue. For example, discuss a comment 
about proof of structure and a comment about load static tests 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.

Background

What Events Have Caused This Proposed Policy?

    After reviewing the compliance methods in Advisory Circular (AC) 
23-17, the directorate determined there was additional information 
related to the compliance methods in AC 23-17, paragraph 23.683, that 
might be beneficial. A proposed policy memorandum, ACE-00-23.683-01, 
was published on January 12, 2000 (65 FR 1941) for review and comment. 
We received several comments. Nevertheless, after the closing date of 
comments (February 11, 2000), the FAA received a few requests to extend 
the comment period and accept more comments on the proposed policy 
statement. On April 25, 2000, AC 23-17 incorporated paragraph 23.683 
and cancelled AC 23.683-1.
    After publishing the proposed policy, we learned it would be 
beneficial to clarity that this modified method, which accounts for the 
deformation effects of adjacent structure through testing, may not be 
necessary for some designs. In some cases, analysis may be used to 
account for these effects. This clarification is inserted under the 
``General Statement of Policy'' of the policy memo ACE-00-23.683-01.
    This notice announces the revised policy memo and gives all 
interested persons the opportunity to present their comments.

What Is the General Effect of This Proposed Policy

    The FAA is presenting this information as a set of guidelines 
suitable for use. However, this document is not intended to establish a 
binding norm; it does not constitute a new regulation and the FAA would 
not apply or rely on it as a regulation. The FAA Aircraft Certification 
Offices (ACO's) that certify normal, utility, acrobatic, and commuter 
category airplanes should try to follow this policy when appropriate.
    Applicants should expect the certificating officials to consider 
this policy when making findings of compliance relevant to new 
certificate actions. Applicants also may consider the material 
contained in this proposed policy statement as a supplement to that 
contained in AC 23-17, paragraph 23.683, when developing a means of 
compliance with the relevant certification standards.
    As with all advisory material, this statement of policy identifies 
one method, but not the only method, of compliance.

[[Page 14244]]

    Because this proposed general statement of policy only announces 
what the FAA seeks to establish as policy, the FAA considers it an 
issue suitable for public comment. Therefore, the FAA invites comments 
on the following proposed general statement of policy relevant to 
compliance with Sec. 23.305, paragraph (a), and other related 
regulations.

The Proposed Policy

General Statement of Policy

    The method of showing compliance with Sec. 23.683 presented in AC 
23-17, paragraph 23.683, Operation Tests, discusses only the control 
system. It does not explicitly specify the consideration of loading on 
adjacent structures and elements. This is consistent with the wording 
in Sec. 23.683 of the regulations. Testing, not analysis, must be used 
to show compliance with Sec. 23.683. There are other regulations, 
related to Sec. 23.683, which must also be met. These include the 
following:
    The first one, which is noted in AC 23-17, is section 23.305, 
paragraph (a), [Subpart C--Structure, General] Strength and 
Deformation. It requires that ``At any load up to limit loads, the 
deformation may not interfere with safe operation.''
    Section 23.307, [Subpart C--Structure, General] Proof of Structure, 
states that ``Compliance with the strength and deformation requirements 
of Sec. 23.305 must be shown for each critical load condition. 
Structural analysis may be used only if the structure conforms to those 
for which experience has shown this method to be reliable. In other 
cases, substantiating load tests must be made.''
    Section 23.655, paragraph (a), [Subpart D--Design and Construction, 
Control Surfaces] Installation, requires that ``Moveable surfaces must 
be installed so that there is no interference between any surfaces, 
their bracing, or adjacent fixed structure, when one surface is held in 
its most critical clearance positions and the others are operated 
through their full movement.''
    Section 23.681, paragraph (a), [Subpart D--Design and Construction, 
Control Surfaces] Limit Load Static Tests, requires that ``Compliance 
with the limit load requirements of this part must be shown by tests in 
which--
    (1) The direction of the test loads produces the most severe 
loading in the control system; and
    (2) Each fitting, pulley, and bracket used in attaching the system 
to the main structure is included.''
    To ensure that these requirements will be satisfied in the conduct 
of the control system operation test, inclusion of loads on the 
adjacent structures or elements in the testing set-up is generally 
required.
    While testing is required for demonstration of compliance to 
Sec. 23.683, in some cases, analysis may be acceptable for showing 
compliance with Sec. 23.305, paragraph (a). Section 23.307, paragraph 
(a), provides the criterion for when analysis is not acceptable and 
testing must be performed.
    It is not appropriate to define specific quantitative criterion to 
determine when testing is required to demonstrate compliance with 
Sec. 23.305, paragraph (a), in accordance with Sec. 23.307, paragraph 
(a). One specific criterion will not work for all possible airplane 
designs. It is better that such determinations are made on a case-by-
case basis, in which the appropriate details of a particular design can 
be considered.
    However, this policy will describe some of the factors that should 
be considered when determining if testing is required to demonstrate 
that clearance between controls and adjacent structure under load meets 
Sec. 23.305, paragraph (a). These factors include, but are not limited 
to, the following:
    (1) The clearance between control surfaces and adjacent structure, 
when at rest. Suppose an applicant has experience with other airplanes 
that have a half-inch of clearance between controls and adjacent 
structure at rest. However, a new design is similar except it now has 
only a tenth of an inch clearance when at rest. Testing to demonstrate 
compliance with Sec. 23.305, paragraph (a), may be required because the 
new structure may not conform to those for which experience has shown 
this method to be reliable in the past. The accuracy of past methods 
may not be suitable for the smaller clearances. Conditions assessed in 
past analysis may not have included a condition that is critical for 
the new smaller clearance.
    (2) The amount of deformation (under limit loads) in the control 
surface or adjacent structure. If analysis had been shown to be 
reliable in the past for a wing that had much smaller deflections than 
a current design, the current structure may not conform to those for 
which experience has shown this method to be reliable, and testing may 
be required. Previous analytical methods may no longer be reliable 
because the new design behaves in a more non-linear manner. It is 
possible that types of deflection that were neglected in past analysis 
may now become critical.
    (3) New control surface attachment configurations or other local 
design changes that could create new types of deformation that are 
critical for the new design but were not included in past analysis. If 
the FAA requires (or if an applicant voluntarily chooses) compliance 
with Sec. 23.305, paragraph (a), to be shown by test, the following 
test procedure is one means to simultaneously demonstrate compliance 
with both Sec. 23.305, paragraph (a), and Sec. 23.683. It also 
demonstrates compliance with Sec. 23.681, paragraph (a). This testing 
may be conducted as follows:
    Except where otherwise specified, the tests described below in 
sections (1), (2), and (3) should be conducted within the following 
parameters.
    a. Conduct the control system operation tests by operating the 
controls from the pilot's compartment.
    b. All the control surfaces must be installed in accordance with 
the type design to their adjacent fixed surface on the airframe.
    c. The entire control system and adjacent fixed structure should be 
loaded.
    d. The adjacent fixed surfaces (wings, horizontal stabilizers, 
vertical stabilizers, and so forth) should be loaded to provide 
deflections equivalent to critical limit load flight conditions.
    e. The structure deflections should correspond to the limit flight 
conditions that represent the worst case conditions for increased cable 
tension, decreased cable tension, and control/fixed surface proximity 
for each control system as appropriate.
    f. The entire control system must be loaded to either the limit 
airloads or the limit pilot forces, whichever is less (Sec. 23.683, 
paragraph (b)(1)).
    g. Minimum clearances around control surfaces and minimum tensions 
in cable systems should be defined to be incorporated in the airplane's 
instructions for continued airworthiness. The test article should 
incorporate these minimum clearances and tensions, unless you otherwise 
account for them.
    h. If reductions in the minimum clearances described in paragraph g 
above are possible due to environmental conditions expected in service, 
you must account for this. This can be accomplished through analysis or 
during testing by adjusting the test article clearances to encompass 
these effects.
    (1) The tests described in this section support the demonstration 
that the control system is free from jamming, excessive friction, and 
excessive deflection as required by Sec. 23.683, paragraphs (a)(1), 
(2), and (3). They also support the demonstration that structural 
deformations not interfere

[[Page 14245]]

with safe operation as required by Sec. 23.305, paragraph (a). 
Accomplish the following:
    (i) Load the adjacent fixed aerodynamic surface (wing, horizontal 
tail, or vertical tail) in accordance with one of the conditions of 
paragraphs d and e above.
    (ii) Support the control surface being tested while it is located 
in the neutral position.
    (iii) Load the control surfaces to the critical limit loads, as 
described in paragraph f above, and evaluate their proximity to the 
fixed adjacent structure for interference (contact).
    (iv) Load the pilot's control until the control surface is just off 
the support.
    (v) Determine the available control surface travel, which is the 
amount of movement of the surface from neutral when the cockpit control 
is moved through the limits of its travel.
    (vi) The control surface under loads described in paragraph f above 
should travel a minimum of 10 percent of the total unloaded travel, as 
measured from the neutral position. This should be demonstrated for 
both directions of travel.
    (vii) To address the possibility of a critical intermediate control 
surface loading, gradually remove load from the control surface (while 
maintaining the load on the adjacent fixed surface) until maximum 
control surface travel is achieved.
    (viii) The above procedure should be repeated in the opposite 
direction.
    (ix) With limit load applied to the adjacent fixed surface and 
limit or intermediate load applied to the control surface, no signs of 
jamming, or of any permanent set of any connection, bracket, 
attachment, and so forth, may be present.
    (x) The control system should operate freely without excessive 
friction.
    (xi) Cable systems should be checked with the loads applied to 
ensure that excessive slack does not develop in the system.
    (xii) Repeat this process for each of the critical loading 
conditions as defined by paragraphs d and f above.
    (2) The tests described in this section support the demonstration 
that structural deformations not interfere with safe operation as 
required by Sec. 23.305, paragraph (a). Accomplish the following:
    (i) Load the adjacent fixed aerodynamic surface (wing, horizontal 
tail, or vertical tail) in accordance with one of the conditions of 
paragraph d and e above.
    (ii) Operate the unloaded control system from stop to stop.
    (iii) No signs of interference (contact) may be present.
    (iv) The control system should operate freely without excessive 
friction.
    (v) Repeat this process for each of the critical adjacent fixed 
surface loading conditions as defined by paragraphs d and e above.

    Note 1: An alternate procedure may be used to accommodate the 
testing described in sections (1) and (2) above during structural 
tests of a partial airplane. This method requires that all control 
system components that are attached to or enclosed by the loaded 
test structure be installed per type design. A sufficiently 
representative mockup of remaining control system components must be 
used to ensure that the full length of any cables which extend from 
the loaded test structure are included. This is necessary to make a 
reasonable assessment that slack that could develop in control 
cables is not excessive enough to cause an entanglement or jam. The 
control surface activation may be input at any convenient location 
between the mockup terminus and the cockpit.

    (3) The tests described in this section will demonstrate that the 
control system is free from excessive deflection as required by 
Sec. 23.683, paragraph (a)(3). These tests complete the demonstration 
that the control system is free from jamming and excessive friction, as 
required by Sec. 23.683, paragraphs (a)(1) and (2). They also 
demonstrate that structural deformations do not interfere with safe 
operation, as required by Sec. 23.305, paragraph (a). These tests meet 
the limit load static test requirements of Sec. 23.681, paragraph (a). 
Accomplish the following:
    (i) With the adjacent fixed surface (wing, horizontal tail, or 
vertical tail) unloaded, support the control surface being tested while 
it is located in the neutral position.
    (ii) Load the control surfaces to the critical limit loads, as 
described in paragraph f above, and evaluate their proximity to the 
fixed adjacent structure for jamming or contact.
    (iii) Load the pilot's control until the control surface is just 
off the support.
    (iv) Operate the cockpit control in the direction opposite the load 
to the extent of its travel.
    (v) The above procedure should be repeated in the opposite 
direction.
    (vi) The minimum loaded control surface travel from the neutral 
position in each direction is 10 percent of the total unloaded control 
surface travel.
    (vii) Under limit load, no signs of jamming, or of any permanent 
set of any connection, bracket, attachment, and so forth, may be 
present.
    (viii) The control system should operate freely without excessive 
friction.

    Note 2: The tests described in section (3) above are normally 
accomplished using a complete airplane. As a minimum, they must be 
completed using an airframe/control system that completely 
represents the final product from the cockpit controls to the 
control surface.

    Regardless of the amount of travel of a control surface when tested 
as described above, the airplane must have adequate flight 
characteristics as specified in Sec. 23.141. Any airplane that is a 
close derivative of a previous type certificated airplane need not 
exceed the control surface travel of the original airplane; however, 
the flight characteristics should be tested to ensure compliance.

    Issued in Kansas City, Missouri, on February 22, 2001.
David R. Showers,
Acting Manager, Small Airplane Directorate Aircraft Certification 
Service.
[FR Doc. 01-5603 Filed 3-8-01; 8:45 am]
BILLING CODE 4910-13-M