[Federal Register Volume 66, Number 219 (Tuesday, November 13, 2001)]
[Proposed Rules]
[Pages 56783-56785]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-28334]


 ========================================================================
 Proposed Rules
                                                 Federal Register
 ________________________________________________________________________
 
 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.
 
 ========================================================================
 

  Federal Register / Vol. 66, No. 219 / Tuesday, November 13, 2001 / 
Proposed Rules  

[[Page 56783]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2001-NM-251-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of two existing 
airworthiness directives (AD), applicable to certain Boeing Model 737 
series airplanes, that currently include replacing the main rudder 
power control unit (PCU) and PCU vernier control rod bolts; testing the 
main rudder PCU to detect certain discrepancies and to verify proper 
operation of the PCU; and revising the FAA-approved Airplane Flight 
Manual procedures to correct a jammed or restricted flight control 
condition. Instead, this new proposal would require installation of a 
new rudder control system and changes to the adjacent systems to 
accommodate that new rudder control system. This proposal is prompted 
by FAA determinations that the existing system design architecture is 
unsafe due to inherent failure modes, including single-jam modes and 
certain latent failures or jams, which, when combined with a second 
failure or jam, could cause an uncommanded rudder hardover event and 
consequent loss of control of the airplane. Additionally, the current 
rudder operational procedure is not effective throughout the entire 
flight envelope. The actions specified by the proposed AD are intended 
to prevent the identified unsafe condition.

DATES: Comments must be received by January 14, 2002.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 2001-NM-251-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9 a.m. and 3 p.m., Monday through Friday, except 
Federal holidays. Comments may be submitted via fax to (425) 227-1232. 
Comments may also be sent via the Internet using the following address: 
[email protected]. Comments sent via fax or the Internet must 
contain ``Docket No. 2001-NM-251-AD'' in the subject line and need not 
be submitted in triplicate. Comments sent via the Internet as attached 
electronic files must be formatted in Microsoft Word 97 for Windows or 
ASCII text.

FOR FURTHER INFORMATION CONTACT: Kenneth W. Frey, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington; 
telephone (425) 227-2673; 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 action may be changed in 
light of the comments received.
    Submit comments using the following format:
     Organize comments issue-by-issue. For example, discuss a 
request to change the compliance time and a request to change the 
service bulletin reference as two separate issues.
     For each issue, state what specific change to the proposed 
AD is being requested.
     Include justification (e.g., reasons or data) for each 
request.
    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 action must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 2001-NM-251-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-114, Attention: Rules 
Docket No. 2001-NM-251-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On June 23, 1997, the FAA issued AD 97-14-04, amendment 39-10061 
(62 FR 35068, June 30, 1997), applicable to certain Boeing Model 737-
100, -200, -300, -400, and ``500 series airplanes. That AD includes the 
following requirements:
     Replacement of the main rudder power control unit (PCU) 
with a newly designed unit.
     Tests of the main rudder PCU to detect excessive internal 
leakage of hydraulic fluid, stalling, or reversal, and to verify proper 
operation of the PCU.
     Replacement of the vernier control rod bolts with newly 
designed bolts.
    The actions of AD 97-14-04 were prompted by extensive laboratory 
testing indicating that a single jammed secondary slide in the main 
rudder PCU servo valve could result in an uncommanded rudder hardover 
event, opposite to the pilot-commanded input. That AD also was prompted 
by reports of fracturing of the vernier control rod bolts as a result 
of the shank of the bolt running into the threads on the nutplate 
during installation of the rod. The requirements of that AD are 
intended to prevent certain single jams in the dual concentric servo 
valve from causing uncommanded rudder hardovers, loss of hinge moment 
due to excessive internal leakage in the rudder control system, and 
fracturing of the vernier control rod bolts, all of which could reduce 
the controllability of the airplane.

[[Page 56784]]

    On October 20, 2000, the FAA issued AD 2000-22-02, amendment 39-
11948 (65 FR 64134, October 26, 2000), applicable to all Boeing Model 
737 series airplanes. That AD supersedes AD 96-26-07, amendment 39-9871 
(62 FR 15, January 2, 1997), to require revising the FAA-approved 
Airplane Flight Manual (AFM) procedure in AD 96-26-07 to simplify the 
instructions for correcting a jammed or restricted flight control 
condition. AD 2000-22-02 was prompted by an FAA determination that the 
procedure inserted in the AFM by AD 96-26-07 was not defined 
adequately. The actions specified in AD 2000-22-02 are intended to 
ensure that the flight crew is advised of the procedures necessary to 
address a condition involving a jammed or restricted rudder. To correct 
the format for certain AFM material described in AD 2000-22-02, on 
November 9, 2000, the FAA issued AD 2000-22-02 R1, amendment 39-11948 
(65 FR 69239, November 16, 2000).

Actions Since Issuance of Previous Rules

    Since the issuance of AD 97-14-04, the National Transportation 
Safety Board (NTSB) has identified the most probable cause of two major 
airplane accidents as a jammed secondary slide in the main rudder PCU 
servo valve in combination with overtravel of the primary slide. While 
that AD addressed what was considered to be the most likely cause of 
uncommanded rudder hardovers, the FAA recognized that other causes were 
still possible.
    Subsequently, the FAA determined that the existing system design 
architecture is unsafe due to inherent failure modes, including single-
jam modes and certain latent failures or jams, which, when combined 
with a second failure or jam, could cause an uncommanded rudder 
hardover event and consequent loss of control of the airplane. These 
failure modes remain even following accomplishment of the actions 
required by AD 97-14-04.
    In addition, the FAA has received information from the Independent 
737 Flight Controls Engineering Test and Evaluation Board (ETEB) 
verifying the existence of the failure modes described above in the 
rudder system of all Model 737 series airplanes that can cause an 
uncommanded rudder hardover.
    Because of the existing design architecture, the FAA issued the 
previously described AD 2000-22-02 R1 to include a special non-normal 
operational ``Uncommanded Rudder'' procedure, which provides necessary 
instructions to the flight crew for control of the airplane during an 
uncommanded rudder hardover event. The revised rudder procedure 
included in AD 2000-22-02 R1 is implemented to provide the flight crew 
with a means to recover control of the airplane following certain 
failures of the rudder control system. However, such a procedure, which 
is unique to the Model 737 series airplane, adds to the workload of the 
flight crew at a critical time when the flight crew is attempting to 
recover from an uncommanded rudder movement or other system 
malfunction. While that procedure effectively addresses certain rudder 
system failures, the FAA finds that such a procedure will not be 
effective in preventing an accident if the rudder control failure 
occurs during takeoff or landing.
    For these reasons, the FAA has determined that the need for a 
unique operational procedure and the inherent failure modes in the 
existing rudder control system, when considered together, present an 
unsafe condition. In light of these reasons, the FAA proposes to 
eliminate the unsafe condition by mandating incorporation of a newly 
designed rudder control system. The manufacturer is currently 
redesigning the rudder system to eliminate these rudder failure modes. 
The redesigned rudder control system will incorporate design features 
that will increase system redundancy, and will add an active fault 
monitoring system to detect and annunciate to the flight crew single 
jams in the rudder control system. If a single failure or jam occurs in 
the linkage aft of the torque tube, the new rudder design will allow 
the flight crew to control the airplane, using normal piloting skills, 
without operational procedures that are unique to this airplane model.

FAA's Conclusions

    The FAA has identified failure modes in the Model 737 rudder 
control system that could cause loss of control of the airplane if a 
single jam occurs, or if a single failure combined with a latent 
failure occurs. For these reasons, the FAA concludes that a full 
redesign of the rudder is warranted, based on the knowledge that single 
jams and single failures with latent failures in the flight control 
system can cause loss of control 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 supersede AD 97-14-04 and AD 2000-22-02 R1 to require 
installation of a new rudder control system and applicable changes to 
the adjacent systems to accommodate the new rudder control system on 
all Model 737 series airplanes. These actions would be required to be 
accomplished in accordance with a method approved by the FAA. Boeing 
indicates that a new rudder control system is currently being 
developed, which the FAA intends to evaluate for possible approval as 
an alternative method of compliance to this proposed AD.
    The new design for the Model 737 rudder control system located at 
the aft end of the airplane will include the installation of new or 
modified components for the rudder control system. Such components will 
include an aft torque tube, hydraulic actuators, and associated control 
rods; and additional wiring throughout the airplane to support failure 
annunciation of the rudder control system in the flight deck. The new 
design also will incorporate two separate inputs, each with an override 
mechanism, to two separate servo valves on the main rudder PCU. The 
input to the standby PCU also will include an override mechanism. In 
addition, changes to the adjacent systems will be necessary, such as 
changes to the flight deck indication and standby hydraulic system 
control.

Cost Impact

    There are approximately 4,500 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 2,000 
airplanes of U.S. registry would be affected by this proposed AD.
    The new installation action that is proposed in this AD would take 
approximately 700 hours per airplane to accomplish, at an average labor 
rate of $60 per work hour. Required parts would cost approximately 
$140,000 per airplane. Based on these figures, the cost impact of the 
currently required actions on U.S. operators is estimated to be 
$364,000,000 (over the proposed 5-year compliance time), or $182,000 
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 the action in the 
future if this AD were not adopted. The cost impact figures discussed 
in AD rulemaking actions represent only the time necessary to perform 
the specific actions actually required by the AD. These figures 
typically do not include incidental costs, such as the time required to 
gain access and close up, planning time, or time necessitated by other 
administrative actions.

[[Page 56785]]

Regulatory Impact

    The regulations proposed herein would not have a substantial direct 
effect 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, it 
is determined that this proposal would not have federalism implications 
under Executive Order 13132.
    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 removing amendment 39-10061 (62 FR 
35068, June 30, 1997) and amendment 39-11948 (65 FR 69239, November 16, 
2000), and by adding a new airworthiness directive (AD), to read as 
follows:

Boeing: Docket 2001-NM-251-AD. Supersedes AD 97-14-04, Amendment 39-
10061; and AD 2000-22-02 R1, Amendment 39-11948.

    Applicability: All Model 737 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 (b)(1) 
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 an uncommanded rudder hardover event and consequent 
loss of control of the airplane due to inherent failure modes, 
including single-jam modes, and certain latent failure or jams 
combined with a second failure or jam; accomplish the following:

Installation

    (a) Within 5 years after the effective date of this AD, do the 
actions required by paragraphs (a)(1) and (a)(2) of this AD, in 
accordance with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA.
    (1) Install a new rudder control system that includes new 
components such as an aft torque tube, hydraulic actuators, and 
associated control rods, and additional wiring throughout the 
airplane to support failure annunciation of the rudder control 
system in the flight deck. The system also must incorporate: two 
separate inputs, each with an override mechanism, to two separate 
servo valves on the main rudder power control unit (PCU); and an 
input to the standby PCU that will also include an override 
mechanism.
    (2) Make applicable changes to the adjacent systems to 
accommodate the new rudder control system.

Alternative Methods of Compliance

    (b)(1) 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. 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.
    (2) Alternative methods of compliance, approved previously in 
accordance with AD 97-14-04, amendment 39-10061, are not considered 
to be approved as alternative methods of compliance with this AD.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (c) 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 November 6, 2001.
Vi L. Lipski,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-28334 Filed 11-9-01; 8:45 am]
BILLING CODE 4910-13-U