[Federal Register Volume 61, Number 168 (Wednesday, August 28, 1996)]
[Proposed Rules]
[Pages 44232-44234]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-21878]


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


DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-146-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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

SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737 series 
airplanes. This proposal would require replacement of the flow 
restrictors of the aileron and elevator power control units (PCU's) 
with new flow restrictors. 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 reduced 
roll and/or pitch rate control of the airplane and consequent increased 
pilot workload as a result of fragments from a deteriorated flow 
restrictor filter screen becoming lodged in the PCU.

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-146-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: Don Kurle, Senior 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) 227-2798; 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

[[Page 44233]]

postcard on which the following statement is made: ``Comments to Docket 
Number 96-NM-146-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-146-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.

Report Received by FAA

    The FAA received a report indicating that, prior to its 
installation on a Model 737 series airplane, an aileron/elevator power 
control unit (PCU) failed a functional test for maximum rate 
capability. Investigation revealed that the PCU was contaminated at the 
main control valve. The source of this contamination was a filter 
screen from a flow restrictor. These filter screens were manufactured 
using a new forming process that results in deterioration of the 
screens when proof pressure is applied during functional testing.
    If the filter screen deteriorates, fragments of the screen could 
migrate to the main control valve, the damping orifice, or the bypass 
valve. If a fragment lodges in the main control valve, one of the 
slides could jam or a control port could be blocked partially. A jammed 
slide could result in reduced hinge moment of the PCU and reduced rate 
capability of the elevator or aileron in one direction. A partially 
blocked control port could result in reduced aileron/spoiler or 
elevator maximum rate and, consequently, reduction of the airplane 
pitch or roll rate capability. Lodging of a fragment in the damping 
orifice could result in blockage of the orifice and consequent small 
amplitude aileron or elevator limit cycling on the ground.
    Jamming of the bypass valve in the power-off (bypass) position 
could cause one PCU to remain unpowered. The other PCU will continue to 
function at its full capacity, but the total surface hinge moment and 
maximum airplane pitch or roll rate capability will be reduced. 
Subsequent loss of hydraulic power to the other PCU could result in 
manual reversion control of the elevator or ailerons.
    Jamming of the bypass valve in the power-on position would have no 
effect on the operation of the system as long as both hydraulic systems 
remain powered. If the hydraulic system that powers the non-
contaminated PCU is lost, the effect would be essentially the same as 
if a bypass valve jams in the bypass condition: one PCU will be 
unpowered, and the contaminated PCU will continue to function at its 
full capacity, but the total surface hinge moment and maximum airplane 
pitch or roll rate capability will be reduced. If the hydraulic system 
that powers the contaminated PCU is lost, the other PCU will continue 
to function at its full capacity. However, the maximum aileron/spoiler 
or elevator maximum rate would be reduced and, consequently, pitch or 
roll rate would be reduced because the contaminated PCU will not go 
into bypass mode.
    Reduced roll and/or pitch rate control of the aileron could result 
in increased pilot workload.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Letter 737-SL-27-
71-A, dated June 19, 1992, including Attachment 1, which describes 
procedures for replacement of the four flow restrictors, part number 
(P/N) JETA1875500D, on the aileron and elevator PCU's, P/N 65-45180-29, 
serial numbers 182 through 1297 inclusive, with flow restrictors having 
P/N JETX0527100B.

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 replacement of the flow restrictors of the 
aileron and elevator power control units (PCU's) with new flow 
restrictors. The actions would be required to be accomplished in 
accordance with the service letter described previously.

Explanation of Proposed Compliance Time

    In developing an appropriate compliance time for the proposed 
replacement, the FAA's intent is that it 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. The FAA finds that 18 months corresponds closely to 
the interval representative of most of the affected operators' normal 
maintenance schedules. The FAA considers that this interval will 
provide an acceptable level of safety.

Cost Impact

    There are approximately 244 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 146 
airplanes of U.S. registry would be affected by this proposed AD, that 
it would take approximately 12 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 $2,960 per airplane. 
Based on these figures, the cost impact of the proposed AD on U.S. 
operators is estimated to be $537,280, or $3,680 per airplane.
    The cost impact figure discussed above is 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.

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,

[[Page 44234]]

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.


Sec. 39.13  [Amended]

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

Boeing: Docket 96-NM-146-AD.

    Applicability: Model 737 series airplanes equipped with an 
aileron or elevator power control unit (PCU) having part number (P/
N) 65-45180-29, serial numbers 182 through 1297 inclusive; 
certificated in any category.

    Note 1: Originally, aileron or elevator PCU's having P/N's and 
serial numbers identified in the applicability of this AD may have 
been installed on Model 737 series airplanes having line numbers 
1793 through 2036 inclusive. In addition, some of these PCU's may 
have been used as spares; therefore, specific airplane line numbers 
equipped with such PCU's cannot be provided in this AD.
    Note 2: PCU's having P/N 65-45180-29 consist of a PCU assembly 
having P/N 65-44761-21 plus associated hydraulic fittings. Both PCU 
P/N's 65-45180-29 and 65-44761-21 are serialized. PCU's subject to 
the requirements of this AD may be more easily identified using 
serial numbers for P/N 65-44761-21. The following serial numbers 
correspond to P/N 65-44761-21:

8549A,
8550A,
8552A,
8556A,
8557A,
8561A,
8563A through 8718A inclusive,
8720A through 8726A inclusive,
8728A through 8745A inclusive,
8749A,
8750A through 8758A inclusive,
8760A through 8873A inclusive,
8876A through 9004A inclusive,
9007A through 9012A inclusive,
9014A through 9040A inclusive,
9042A through 9066A inclusive,
9068A through 9340A inclusive,
9342A through 9388A inclusive,
9390A through 9529A inclusive,
9531A through 9676A inclusive, and
9678A through 9688A inclusive.

    Note 3: 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 reduced roll and/or pitch rate control of the aileron 
and consequent increased pilot workload, accomplish the following:
    (a) Within 18 months after the effective date of this AD, 
replace the four flow restrictors, part number (P/N) JETA1875500D, 
on the aileron and elevator power control units (PCU's), P/N 65-
45180-29, serial numbers 182 through 1297 inclusive, with flow 
restrictors having P/N JETX0527100B, in accordance with Boeing 
Service Letter 737-SL-27-71-A, dated June 19, 1992, including 
Attachment 1.
    (b) As of the effective date of this AD, no person shall install 
a flow restrictor having P/N JETA1875500D on an aileron or elevator 
PCU having P/N 65-45180-29, serial numbers 182 through 1297 
inclusive, of any airplane.
    (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 4: 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. 96-21878 Filed 8-23-96; 9:01 am]
BILLING CODE 4910-13-U