[Federal Register Volume 62, Number 122 (Wednesday, June 25, 1997)]
[Proposed Rules]
[Pages 34185-34187]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-16569]


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 Proposed Rules
                                                 Federal Register
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
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  Federal Register / Vol. 62, No. 122 / Wednesday, June 25, 1997 / 
Proposed Rules  

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-45-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, 
and -500 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to all Boeing Model 737-100, -200, -
300, -400, and -500 series airplanes. This proposal would require 
removing the yaw damper coupler; replacing its internal rate gyroscope 
with a new or overhauled unit; and performing a test to verify the 
integrity of the yaw damper coupler, and repair, if necessary. This 
proposal is prompted by an FAA determination that requiring replacement 
of the internal rate gyroscope will significantly increase the 
reliability of the yaw damper coupler system. The actions specified by 
the proposed AD are intended to prevent sudden uncommanded yawing of 
the airplane due to potential failures within the yaw damper system, 
and consequent injury to passengers and crewmembers.

DATES: Comments must be received by July 21, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 97-NM-45-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal 
holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Hania Younis, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington; 
telephone (425) 227-2764; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 97-NM-45-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules 
Docket No. 97-NM-45-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On August 21, 1996, the FAA issued a notice of proposed rulemaking 
(NPRM), Docket Number 96-NM-151-AD (61 FR 44243, August 28, 1996), 
applicable to all Boeing Model 737-100, -200, -300, -400, and -500 
series airplanes, which proposed to require repetitive tests to verify 
the integrity of the yaw damper coupler, and various follow-on actions. 
That NPRM also proposed to require a one-time inspection to determine 
the part number of the engage solenoid valve of the yaw damper, and 
replacement of the valve with a valve having a different part number, 
if necessary. That NPRM was prompted by a review of the design of the 
flight control systems on Model 737 series airplanes. The actions 
specified by that proposed AD were intended to prevent sudden 
uncommanded yawing of the airplane due to potential failures within the 
yaw damper system, and consequent injury to passengers and crewmembers.

Actions Since Issuance of the NPRM

    Since the issuance of the NPRM described previously, the FAA has 
determined that the requirements contained in paragraph (b) of the NPRM 
must be expanded to require hard-time replacement of the internal rate 
gyroscope of the yaw damper coupler. That paragraph originally proposed 
to require, in part, replacement of the internal rate gyroscope only if 
necessary following testing. The FAA made this determination based on 
data submitted by Boeing, which indicates that requiring replacement of 
the internal rate gyroscope within a specified time will significantly 
increase the reliability of the yaw damper coupler system. The FAA 
finds that such hard-time replacement is necessary in order to address 
the unsafe condition identified in the original NPRM (i.e., sudden 
uncommanded yawing of the airplane due to potential failures within the 
yaw damper system, and consequent injury to passengers and 
crewmembers).
    In addition, a commenter to the original NPRM suggests that it be 
separated into two independent AD's--one action to address the internal 
rate gyroscope, and the other action to address the engage solenoid 
valve. The commenter states that the actions required for each of these 
parts are

[[Page 34186]]

sufficiently different that recordkeeping requirements warrant separate 
rules.
    In response to that commenter, the FAA determined that issuance of 
two separate AD's is appropriate. Therefore, on April 24, 1997, the FAA 
issued AD 97-09-15, amendment 39-10011 (62 FR 24325, May 5, 1997), to 
require accomplishment of the actions contained in the original NPRM 
that address the engage solenoid valve. [Those actions appeared in 
paragraph (b) of the original NPRM.] This proposed rule addresses 
actions contained in the original NPRM that are associated with the 
internal rate gyroscope of the yaw damper coupler. [Those actions 
appeared in paragraph (a) of the original NPRM.]
    Additionally, on March 7, 1997, the FAA issued an NPRM to require 
installation of a newly designed rudder-limiting device and yaw damper 
system [reference Docket 97-NM-28-AD (62 FR 12121, March 14, 1997)]. 
That proposal was issued in response to a number of reports of 
malfunctions of the yaw damper system, which may have been caused by 
failure of the internal rate gyroscope of the yaw damper coupler as a 
result of wear of the rotor bearing, and contamination and shorting of 
the electrical connectors or surface position sensors in the area of 
the yaw damper servo-actuator. Such malfunctions of the yaw damper 
system, if not corrected, could result in sudden uncommanded yawing of 
the airplane and consequent injury to passengers and crewmembers.
    Boeing advised the FAA that it has designed a rudder-limiting 
device and a new yaw damper for installation on the latest versions of 
Model 737 series airplanes currently undergoing certification. Both of 
these systems are capable of being installed on the existing fleet of 
Model 737 series airplanes. (Boeing has not yet released a service 
bulletin reflecting these changes.)
    In light of that information, the FAA made a determination that 
installation of a newly designed rudder-limiting device and yaw damper 
system is required to ensure the safety of the affected fleet. 
Installation of a rudder-limiting device is necessary to reduce the 
rudder authority at altitudes above 1,500 feet above ground level (AGL) 
so that, if any inadvertent hardover occurs, the resultant roll upset 
can be controlled with control wheel inputs. Installation of a new yaw 
damper system is necessary to improve the reliability of the system and 
its fault monitoring capability, which will prevent uncommanded yawing 
of the airplane.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require removing the yaw damper coupler; replacing 
its internal rate gyroscope with a new or overhauled unit; and 
performing a test to verify the integrity of the yaw damper coupler, 
and repair, if necessary. The actions would be required to be 
accomplished in accordance with a method approved by the FAA.

Explanation of Proposed Compliance Times

    This proposal would require that the actions be accomplished within 
6,000 hours time-in-service (for yaw damper couplers on which the last 
maintenance activity occurred within less than 12,000 hours time-in-
service as of the effective date of the AD), or 3,000 hours time-in-
service (for yaw damper couplers on which the last maintenance activity 
occurred within 12,000 hours time-in-service or more as of the 
effective date of the AD). Thereafter, repetitive tests would be 
accomplished every 9,000 hours time-in-service.
    In developing an appropriate compliance time for this action, the 
FAA considered not only the degree of urgency associated with 
addressing the subject unsafe condition, but the availability of 
required parts and the practical aspect of accomplishing the required 
actions within an interval of time that parallels normal scheduled 
maintenance for the majority of affected operators. The repetitive test 
interval was established based on analyses submitted by Boeing; 
accomplishment of tests at this interval will ensure that the overall 
reliability of the yaw damper coupler system is maximized.

Cost Impact

    There are approximately 2,675 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 1,091 
airplanes of U.S. registry would be affected by this proposed AD, that 
it would take between 8 and 13 work hours per airplane to accomplish 
the proposed actions, and that the average labor rate is $60 per work 
hour. Required parts would cost approximately $2,500 per airplane. 
Based on these figures, the cost impact of the proposed AD on U.S. 
operators is estimated to be between $3,251,180 and $3,578,480, or 
between $2,980 and $3,280 per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this AD were not adopted.
    The FAA recognizes that the obligation to maintain aircraft in an 
airworthy condition is vital, but sometimes expensive. Because AD's 
require specific actions to address specific unsafe conditions, they 
appear to impose costs that would not otherwise be borne by operators. 
However, because of the general obligation of operators to maintain 
aircraft in an airworthy condition, this appearance is deceptive. 
Attributing those costs solely to the issuance of this AD is 
unrealistic because, in the interest of maintaining safe aircraft, 
prudent operators would accomplish the required actions even if they 
were not required to do so by the AD.
    A full cost-benefit analysis has not been accomplished for this 
proposed AD. As a matter of law, in order to be airworthy, an aircraft 
must conform to its type design and be in a condition for safe 
operation. The type design is approved only after the FAA makes a 
determination that it complies with all applicable airworthiness 
requirements. In adopting and maintaining those requirements, the FAA 
has already made the determination that they establish a level of 
safety that is cost-beneficial. When the FAA, as in this proposed AD, 
makes a finding of an unsafe condition, this means that the original 
cost-beneficial level of safety is no longer being achieved and that 
the proposed actions are necessary to restore that level of safety. 
Because this level of safety has already been determined to be cost-
beneficial, a full cost-benefit analysis for this proposed AD would be 
redundant and unnecessary.

Regulatory Impact

    The regulations proposed herein would not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government.
    Therefore, in accordance with Executive Order 12612, it is 
determined that this proposal would not have sufficient federalism 
implications to warrant the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44

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FR 11034, February 26, 1979); and (3) if promulgated, will not have a 
significant economic impact, positive or negative, on a substantial 
number of small entities under the criteria of the Regulatory 
Flexibility Act. A copy of the draft regulatory evaluation prepared for 
this action is contained in the Rules Docket. A copy of it may be 
obtained by contacting the Rules Docket at the location provided under 
the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: Docket 97-NM-45-AD.

    Applicability: All Model 737-100, -200, -300, -400, and -500 
series airplanes, certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (c) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent sudden uncommanded yawing of the airplane due to 
potential failures within the yaw damper system, and consequent 
injury to passengers and crewmembers, accomplish the following:
    (a) Remove the yaw damper coupler, replace the internal rate 
gyroscope with a new or overhauled unit, and perform a test to 
verify the integrity of the yaw damper coupler, all in accordance 
with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA, Transport Airplane Directorate, at 
the applicable time specified in paragraph (a)(1) or (a)(2) of this 
AD.
    (1) For airplanes on which the yaw damper coupler has 
accumulated less than 12,000 hours time-in-service since its last 
maintenance activity as of the effective date of this AD: Perform 
the actions within 6,000 hours time-in-service after the effective 
date of this AD; and thereafter at intervals not to exceed 9,000 
hours time-in-service.
    (2) For airplanes on which the yaw damper coupler has 
accumulated 12,000 or more hours time-in-service since its last 
maintenance activity as of the effective date of this AD: Perform 
the actions within 3,000 hours time-in-service after the effective 
date of this AD; and thereafter at intervals not to exceed 9,000 
hours time-in-service.
    (b) If the yaw damper coupler fails the test required by 
paragraph (a) of this AD, prior to further flight, repair the 
coupler in accordance with a method approved by the Manager, Seattle 
ACO.
    (c) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle Aircraft Certification 
Office (ACO), FAA, Transport Airplane Directorate.
    Operators shall submit their requests through an appropriate FAA 
Principal Maintenance Inspector, who may add comments and then send 
it to the Manager, Seattle ACO.
    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (d) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on June 18, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-16569 Filed 6-24-97; 8:45 am]
BILLING CODE 4910-13-U