[Federal Register Volume 61, Number 168 (Wednesday, August 28, 1996)]
[Proposed Rules]
[Pages 44243-44245]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-21883]



[[Page 44243]]

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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-151-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 
repetitive tests to verify the integrity of the yaw damper coupler, and 
various follow-on actions. This proposal also would 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. This proposal is prompted by a 
review of the design of the flight control systems on Model 737 series 
airplanes. 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 October 24, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-151-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 Commercial Flight Systems Group, Air Transport Systems 
Division, Honeywell Inc., Box 21111, Phoenix, Arizona 85036; and 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, Transport Airplane 
Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, 
SW., Renton, Washington 98055-4056; telephone (206) 227-2764; fax (206) 
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 96-NM-151-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. 96-NM-151-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    In October 1994, the FAA organized a team to conduct a Critical 
Design Review (CDR) of the flight control systems installed on Boeing 
Model 737 series airplanes in an effort to confirm the continued 
operational safety of these airplanes. The formation of the CDR team 
was prompted by questions that arose following an accident involving a 
Model 737-200 series airplane that occurred near Colorado Springs, 
Colorado, and one involving a Model 737-300 series airplane that 
occurred near Pittsburgh, Pennsylvania. The CDR team's analysis of the 
flight control systems was performed independent of the investigations 
of these accidents, which are conducted by the National Transportation 
Safety Board (NTSB). The cause of the accidents has not yet been 
determined.
    The CDR team was composed of representatives from the FAA, the 
NTSB, other U.S. government organizations, and foreign airworthiness 
authorities. The team reviewed the service history and the design of 
the flight control systems of Model 737 series airplanes. The team 
completed its review in May 1995. The recommendations of the team 
include various changes to the design of the flight control systems of 
these airplanes, as well as correction of certain design deficiencies. 
This proposed AD is one of nine rulemaking actions being issued by the 
FAA to address the recommendations of the CDR team.

Reports Received by FAA

    The FAA has received a number of reports of uncommanded yawing of 
Boeing Model 737 series airplanes. This condition may have been caused 
by one of two separate failures of the yaw damper system:
    First, the rate gyroscope of the yaw damper coupler can fail as a 
result of wear of the rotor bearing. Such wear can cause increased 
vibration, which may be translated into brinnels (dents) in the gimbal 
bearings. This condition can cause faults in the gyroscope at certain 
input rates and consequent rudder kicks to the yaw damper authority.
    Second, intermittent failures of the engage solenoid valve of the 
yaw damper on the rudder power control units (PCU's) could occur. 
Valves having certain part numbers have encapsulated electrical coils 
(i.e., the coils are coated with a thermoset epoxy moulding compound or 
similar material), which makes the valves less susceptible to damage 
and exposure to moisture. Corrosion could occur if the coils are 
exposed to moisture. Corrosion or damage of the coils could result in 
abrupt uncommanded rudder deflections.
    These conditions, if not corrected, could result in sudden 
uncommanded yawing of the airplane and consequent injury to passengers 
and crewmembers.

FAA's Determinations

    In light of this information, the FAA finds that certain procedures 
must be required to ensure the safety of the affected fleet. These 
procedures include tests to verify the integrity of the yaw damper 
coupler, and various follow-on actions (including tests to verify the 
integrity of the rate gyroscope of the yaw damper coupler; and removal, 
overhaul, replacement, repair, and reinstallation of the rate 
gyroscope), as necessary. The FAA has reviewed the procedures for 
accomplishment of these actions, which are contained in the documents 
described below:

[[Page 44244]]

    1. Honeywell Component Maintenance Manual (CMM) 22-10-27, Revision 
6, dated September 1, 1992. The CMM describes procedures for repetitive 
tests to verify the integrity of the yaw damper coupler; repair of the 
yaw damper coupler, if necessary; removal and reinstallation of the 
rate gyroscope of the yaw damper coupler; replacement of the rate 
gyroscope with a new part; and replacement of the yaw damper coupler 
with a new or serviceable coupler.
    2. Sperry Overhaul Manual 24-09-20, RG1000 Miniature Rate 
Gyroscope, Part No. 2589124-902.'' The overhaul manual describes 
procedures for overhauling the rate gyroscope of the yaw damper 
coupler.
    3. Honeywell Engineering Specification No. IT2589124, ``Integrated 
Test Specification for Rate Gyroscope, Part Number 2589124-902,'' dated 
October 9, 1992. This document describes procedures for tests to verify 
the integrity of the rate gyroscope of the yaw damper coupler.
    Additionally, the Boeing 737 Overhaul Manual specifies procedures 
for a one-time inspection of the engage solenoid valve of the yaw 
damper to determine the part number of the valve, and replacement of 
the valve with a valve having a different part number. The FAA finds 
that the accomplishment of these actions will adequately address 
intermittent failures of the engage solenoid valve. [Operators should 
note that Boeing In-Service Activities Report 95-03-2725-10, dated 
February 16, 1995 (for Model 737-100 and -200 series airplanes), or 95-
04-2725-10, dated February 24, 1995 (for Model 737-300, -400, and -500 
series airplanes), provide additional information concerning 
interchangeability of solenoid valve part numbers.]

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 repetitive tests to verify the integrity of 
the yaw damper coupler, and various follow-on actions. These actions 
would be required to be accomplished in accordance with the Honeywell 
CMM, the Honeywell engineering specification document, and the Sperry 
overhaul manual described previously.
    The proposed AD also would 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. These actions would be required to be 
accomplished in accordance with the Boeing 737 Overhaul Manual 
discussed previously.

Explanation of Proposed Compliance Times

    In developing appropriate compliance times for the proposed 
actions, the FAA's intent is that they be performed during a regularly 
scheduled maintenance visit for the majority of the affected fleet, 
when the airplanes would be located at a base where special equipment 
and trained personnel would be readily available, if necessary. In 
addition, the FAA considered the availability of necessary parts. In 
light of these considerations, the FAA has specified compliance times 
of 3,000 hours time-in-service for accomplishment of the initial tests 
(and 6,000 hours time-in-service for the repetitive tests), and 18 
months for accomplishment of the one-time inspection. The FAA finds 
that these intervals correspond closely to the intervals representative 
of most of the affected operators' normal maintenance schedules. The 
FAA considers that the proposed compliance times will provide an 
acceptable level of safety.

Interim Action

    This proposed AD is considered to be interim action. The 
manufacturer has advised that it currently is developing a modification 
that will positively address the unsafe condition addressed by this AD. 
Once this modification is developed, approved, and available, the FAA 
may consider additional rulemaking.

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.
    The FAA estimates that it would take approximately 4 work hours per 
airplane to accomplish the proposed tests of the yaw damper coupler, 
and that the average labor rate is $60 per work hour. Based on these 
figures, the cost impact of the proposed tests on U.S. operators is 
estimated to be $261,840, or $240 per airplane, per test.
    The FAA estimates that it would take approximately 1 work hour per 
airplane to accomplish the proposed one-time inspection of the engage 
solenoid valve, at an average labor rate of $60 per work hour. Based on 
these figures, the cost impact of the proposed inspection on U.S. 
operators is estimated to be $65,460, or $60 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.
    Should an operator be required to replace an engage solenoid valve 
of the yaw damper, it would take approximately 3 work hours to 
accomplish the replacement, at an average labor rate of $60 per work 
hour. Required parts would cost approximately $1,688 per airplane. 
Based on these figures, the cost impact of any necessary replacement of 
an engage solenoid valve is estimated to be $1,868 per airplane.

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 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.

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Sec. 39.13  [Amended]

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

    Boeing: Docket 96-NM-151-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 
otherwise 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) Within 3,000 hours time-in-service after the effective date 
of this AD, and thereafter at intervals not to exceed 6,000 hours 
time-in-service: Perform tests to verify the integrity of the yaw 
damper coupler, in accordance with procedures specified in the 
Honeywell Component Maintenance Manual 22-10-27, Revision 6, dated 
September 1, 1992.
    (1) If the yaw damper coupler passes the tests, prior to further 
flight, remove the rate gyroscope in accordance with Section 4E, 
page 103, of the Honeywell Component Maintenance Manual; and perform 
tests to verify the integrity of the rate gyroscope, in accordance 
with procedures specified in Honeywell Engineering Specification No. 
IT2589124, ``Integrated Test Specification for Rate Gyroscope, Part 
Number 2589124-902,'' dated October 9, 1992.
    (i) If the rate gyroscope passes the tests, reinstall the rate 
gyroscope in accordance with Section 3F, page 504, of the Honeywell 
Component Maintenance Manual.
    (ii) If the rate gyroscope fails the tests, prior to further 
flight, accomplish either paragraph (a)(1)(ii)(A) or (a)(1)(ii)(B) 
of this AD.
    (A) Overhaul the rate gyroscope in accordance with Sperry 
Overhaul Manual 24-09-20, ``RG1000 Miniature Rate Gyroscope, Part 
No. 2589124-902;'' and reinstall the rate gyroscope in accordance 
with Section 3F, page 504, of the Honeywell Component Maintenance 
Manual. Or
    (B) Replace the rate gyroscope with a new part in accordance 
with Section 3F, page 504, of the Honeywell Component Maintenance 
Manual.
    (2) If the yaw damper coupler fails the tests, prior to further 
flight, accomplish either paragraph (a)(2)(i) or (a)(2)(ii) of this 
AD.
    (i) Repair the coupler in accordance with the Honeywell 
Component Maintenance Manual, and perform tests specified in 
paragraph (a)(1) of this AD to verify the integrity of the rate 
gyroscope. Or
    (ii) Replace the coupler with a new coupler, or with a 
serviceable coupler on which the integrity of the rate gyroscope has 
been verified in accordance with paragraph (a)(1) of this AD. 
Accomplish the replacement in accordance with procedures specified 
in the Honeywell Component Maintenance Manual.
    (b) Within 18 months after the effective date of this AD: 
Perform a one-time inspection of the engage solenoid valve of the 
yaw damper to determine the P/N of the valve. If any valve having P/
N 10-60881-1, -3, or -9 is installed, prior to further flight, 
replace it with a valve having P/N 10-60881-8 or -13. Accomplish the 
actions in accordance with Chapter 27-20-01 of the Boeing 737 
Overhaul Manual.

    Note 2: Boeing In-Service Activities Report 95-03-2725-10, dated 
February 16, 1995 (for Model 737-100 and -200 series airplanes), or 
95-04-2725-10, dated February 24, 1995 (for Model 737-300, -400, and 
-500 series airplanes), provide additional information concerning 
interchangeability of solenoid valve part numbers.

    (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 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 3: 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 August 21, 1996.
Ronald T. Wojnar,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-21883 Filed 8-23-96; 9:03 am]
BILLING CODE 4910-13-U