AD 2002-20-07

[Federal Register Volume 67, Number 194 (Monday, October 7, 2002)]
[Rules and Regulations]
[Pages 62341-62347]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 02-25346]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2001-NM-251-AD; Amendment 39-12903; AD 2002-20-07]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment supersedes seven existing airworthiness 
directives (ADs), applicable to certain Boeing Model 737 series 
airplanes that, among other things, currently require 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 amendment requires installation 
of a new rudder control system and changes to the adjacent systems to 
accommodate that new rudder control system. This amendment 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: Effective November 12, 2002.

ADDRESSES: Information pertaining to this amendment may be obtained 
from or examined at the Federal Aviation Administration (FAA), 
Transport

[[Page 62342]]

Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, 
Washington, 98055-4056.

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: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) by superseding AD 97-14-04, 
amendment 39-10061 (62 FR 35068, June 30, 1997), which is applicable to 
certain Boeing Model 737-100, -200, -300, -400, and -500 series 
airplanes; and AD 2000-22-02 R1, amendment 39-11948 (65 FR 69239, 
November 16, 2000), which is applicable to all Boeing Model 737 series 
airplanes; was published in the Federal Register on November 13, 2001 
(66 FR 56783). The action proposed to require installation of a new 
rudder control system and changes to the adjacent systems to 
accommodate that new rudder control system.

Discussion of Background

    The National Transportation Safety Board (NTSB) has identified the 
most probable cause of two major accidents on Model 737 series 
airplanes as a jammed secondary slide in the main rudder power control 
unit (PCU) servo valve in combination with overtravel of the primary 
slide. While AD 97-14-04 addresses what was considered to be this most 
likely cause of uncommanded rudder hardovers, the FAA recognizes that 
other causes are still possible.
    Subsequently, we 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, amendment 39-10061 (62 FR 35068, June 30, 
1997).
    In addition, we 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, we issued AD 2000-22-
02 R1 to include a special non-normal operational ``Uncommanded 
Rudder'' procedure, which provides necessary instructions to the 
flightcrew 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 flightcrew 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 Model 737 
series airplanes, adds to the workload of the flightcrew at a critical 
time when the flightcrew is attempting to recover from an uncommanded 
rudder movement or other system malfunction. While that procedure 
effectively addresses certain rudder system failures, we find 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, we have 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 this, we proposed 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 flightcrew 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 flightcrew to control 
the airplane, using normal piloting skills, without operational 
procedures that are unique to this airplane model.

Actions Since Issuance of Proposed Rule

    Since the issuance of the notice of proposed rulemaking (NPRM), 
which proposed to require the supersedure of AD 97-14-04 and AD 2000-
22-02 R1, we have determined that this final rule needs to supersede 
five additional ADs, which are listed in the table below. Our decision 
to supersede these ADs was based on a number of factors. First, the new 
rudder control system required by this AD will better address the 
identified unsafe condition through redundancy in the system 
architecture, which will increase reliability. Second, the requirements 
of those ADs will no longer be relevant to or necessary for the new 
rudder control system, since the parts required by those ADs will not 
be included in the design for the new rudder control system. The five 
additional ADs are listed in the table below and described in the 
following paragraphs:

List of ADs To Be Superseded

----------------------------------------------------------------------------------------------------------------
                                              Amendment
                  AD No.                         No.                     Federal Register citation
----------------------------------------------------------------------------------------------------------------
95-06-53..................................  39-9199       60 FR 18981, April 14, 1995.
97-05-10..................................  39-9954       62 FR 9679, March 4, 1997.
97-09-15 R1...............................  39-10912      63 FR 64857, November 24, 1998.
98-02-01..................................  39-10283      63 FR 1903, January 13, 1998.
99-11-05 COR..............................  39-11175      64 FR 27905, May 24, 1999.
----------------------------------------------------------------------------------------------------------------

    [sbull] AD 95-06-53, applicable to all Boeing Model 737 series 
airplanes, requires identification of the part and serial numbers of 
the main rudder PCU; and replacement of certain PCUs with serviceable 
parts, if necessary. That AD corrects an unsafe condition caused by 
improper tooling used to torque the spring retaining nut in the servo 
valve of the main rudder PCU. However, the PCUs identified in AD 95-06-
53 will not be used in the configuration of the new rudder control 
system required by this AD.
    [sbull] AD 97-05-10, applicable to all Boeing Model 737 series 
airplanes, requires removal of the main rudder PCU and replacement with 
a serviceable unit. That AD corrects an unsafe condition due to an 
unapproved Hi-Lock bolt that was installed in the lever assembly 
bearing of the main rudder PCU instead of the correct bolt. However, 
the PCUs identified in AD 97-05-10 will not be used in the 
configuration of the new rudder control system required by this AD.

[[Page 62343]]

    [sbull] AD 97-09-15 R1, applicable to all Boeing Model 737-100, -
200, -300, -400, and -500 series airplanes, requires a one-time 
inspection to determine the part number of the engage solenoid valve of 
the yaw damper on the rudder PCU, and replacement of the valve with a 
valve having a different part number, if necessary. However, the engage 
solenoid valves specified in AD 97-09-15 R1 will not be used in the 
configuration of the new main rudder PCU required by this AD.
    [sbull] AD 98-02-01, applicable to all Boeing Model 737-100, -200, 
-300, -400, and -500 series airplanes, requires 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. However, that configuration of the 
yaw damper coupler, using mechanical rate gyroscopes, is no longer 
approved for installation on Model 737 series airplanes. Instead, AD 
97-14-03, amendment 39-10060 (62 FR 34623, June 27, 1997), requires, 
among other things, installation of a new yaw damper system that 
replaces the gyroscopes specified by AD 98-02-01. That new system is 
intended to prevent malfunction of the yaw damper system.
    [sbull] AD 99-11-05 COR, applicable to all Boeing Model 737 series 
airplanes, requires repetitive displacement tests of the secondary 
slide in the dual concentric servo valve of the PCU for the rudder; and 
replacement of the valve assembly with a modified valve assembly, if 
necessary. However, the dual concentric servo valve of the PCU for the 
rudder, which was specified in AD 99-11-05 COR, will not be used in the 
configuration of the main rudder PCU that will be installed as a 
component of the new rudder control system required by this AD.

Comments

    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. One commenter supports the proposed 
rule. Due consideration has been given to all comments received.

Request to Withdraw Proposal

    One commenter considers that an adequate level of safety has been 
achieved by the accomplishment of AD 97-14-04 and AD 2000-22-02 R1, 
which are referenced in the Discussion paragraph of the proposed rule, 
and by the accomplishment of ADs 95-06-53, 97-05-10, 97-06-09, 97-09-
14, 97-09-15, 97-14-03, 98-02-01, and 99-11-05. The commenter states 
that since accomplishing the modifications required by AD 97-14-03 and 
AD 97-14-04, no instances of uncommanded rudder movement have occurred. 
In addition, no discrepancies were found by the PCU manufacturer during 
numerous displacement tests conducted per AD 99-11-05. Further, the 
proposed rule identifies multiple conditions that only theoretically 
could occur with the existing rudder control system. After reviewing 
this information, we infer that the commenter is requesting withdrawal 
of the proposed rule.
    The FAA does not concur with the commenter's request to withdraw 
the proposed rule. As explained in the proposed rule, the unsafe 
condition is 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. Because the identified 
inherent failure modes have not been eliminated by the actions required 
by those previously issued ADs, we have determined that the actions 
required by this final rule are warranted. This determination was made 
after considering the existence of these failure modes and the need for 
a unique operational procedure (per AD 2000-22-02 R1). No change to the 
final rule is necessary in this regard.

Disagreement With Identified Unsafe Condition

    One commenter, the manufacturer, does not agree that the unsafe 
condition identified in the proposed AD exists in the current Model 737 
rudder control system for the following reasons:
    [sbull] The current rudder control system is safe and has been 
shown to meet all current regulations using accepted industry analysis 
and validation practices.
    [sbull] Service experience accumulated over 116 million flight 
hours demonstrates that the system is safe; the airplane has one of the 
lowest accident rates of airplanes in its class.
    [sbull] All issues identified as potential safety issues have been 
addressed by service bulletins mandated by the following airworthiness 
directives issued by the FAA: AD 97-14-03; AD 97-14-04; AD 97-26-01, 
amendment 39-10244 (62 FR 65597, December 15, 1997); and AD 98-13-12, 
amendment 39-10600 (63 FR 33246, June 18, 1998).
    [sbull] The 737 Flight Controls ETEB report did not identify any 
new significant failure modes or unsafe conditions that invalidate 
previous Model 737 certification documentation. All failure modes in 
the ETEB report had been previously identified and analyzed by the 
manufacturer. The existing rudder system is considered safe and meets 
federal regulations.
    While the manufacturer does not agree that the unsafe condition 
exists, it states that it is committed to a redesign of the Model 737 
rudder control system to further enhance an already safe system. The 
manufacturer also states that the new design will eliminate certain 
potential latent failures in the system, even though evaluation in 
accordance with federal regulations has shown such latencies to be 
acceptable. The elimination of such failures will enable the system to 
be functionally equivalent to a three-actuator system. The new system 
also will eliminate the need for the existing uncommanded rudder non-
normal operational procedure unique to Model 737 series airplanes.
    While the ADs identified by the manufacturer were issued to address 
previously identified unsafe conditions, we have determined that the 
inherent failure modes identified in this AD have not been eliminated 
by the actions required by those ADs. Therefore, we do not agree with 
the manufacturer's conclusion that the existing design of the rudder 
control system is safe. As described in the proposed AD, the unsafe 
condition is 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.
    Likewise, AD 2000-22-02 R1 provides instructions to the flightcrew 
for addressing certain rudder system failures, but those instructions 
will not be effective in preventing an accident if the rudder control 
failure occurs during takeoff or landing.
    After considering all of this information, we have determined that 
it is necessary to issue this AD to eliminate the unsafe condition by 
mandating the installation of a newly designed rudder control system. 
The new system will incorporate design features that will increase 
system redundancy, and will add an active fault monitoring system to 
detect and annunciate to the flightcrew single jams in the rudder 
control system. If a single failure or jam occurs in the linkage aft of 
the torque tube, the new system will allow the flightcrew to control 
the airplane using normal piloting skills, and without using 
operational procedures that are unique to this airplane model. In light 
of this, we consider that the actions specified in

[[Page 62344]]

this final rule are warranted. No change to the final rule is necessary 
in this regard.

Request for Information/Concerns About New Rudder Control System

    One commenter, the NTSB, requested more information on the system 
safety assessment (SSA) being conducted in support of the design 
changes for the proposed new rudder control system. To help evaluate 
the new design, the commenter would like to review the analyses being 
conducted for each design, the reliability benefits, and other rudder 
actuation system designs that were submitted.
    The commenter also stated the following concerns about the new 
system:
    [sbull] It does not provide full independence for the main PCU, and 
``it would appear that true redundancy would require two fully 
independent PCUs.''
    [sbull] The automatic activation system for the standby PCU may 
increase the number of possible failure modes compared to the 
installation of a third full-time independent PCU.
    [sbull] Without the SSA information, the commenter states that it 
is unable to determine if the revisions to the rudder actuation system 
of the Boeing Model 737 series airplanes will sufficiently address 
safety concerns.
    We cannot provide the requested SSA information or other requested 
design information because it is proprietary to The Boeing Company. 
However, we have sent the commenter's request to Boeing. Boeing has 
informed us that it has briefed the NTSB on the Rudder System 
Enhancement Program on January 16, 2001, and on March 18, 2002. To the 
extent that the commenter expresses an interest in certification 
documentation, Boeing will submit the SSA results to us for our 
approval as part of the certification of the new design.
    The commenter also expressed a concern that true redundancy would 
require two fully independent PCUs. During our reviews of the new 
rudder control system, we have found that the new main rudder PCU 
design is equivalent to two independent PCUs. The main rudder PCU is an 
assembly with two PCUs arranged in tandem. The new main rudder PCU will 
have two independent servo valves in lieu of the existing common dual 
concentric servo valve. Two separate input linkages will control the 
position of these valves on the main rudder PCU. The pilot can override 
each of these input linkages and also override the linkage for the 
standby PCU. The function of the override capability is to enable the 
pilot to control the airplane in the event of a jam in any one of the 
three input linkages or associated servo valves in the rudder control 
system.
    Finally, the commenter expressed concerns that the automatic 
activation system for the standby PCU may increase the number of 
failure modes, compared to the installation of a third full-time 
independent PCU. In addressing this concern, we note that introduction 
of a third full-time PCU for a single flight control surface would 
introduce latent failure modes. With three active PCUs, a single PCU 
failure (due to a valve jam or linkage failure) can remain latent while 
the other two PCUs control the rudder surface position. Typically, 
rudder control systems with three active PCUs require frequent periodic 
maintenance to detect a single failure, or require a fault-monitoring 
and annunciation system.
    The introduction of any fault-monitoring system will increase the 
number of failure modes due to increased system complexity. Although 
the fault-monitoring system for the new rudder control system slightly 
increases the number of failure modes, these failure modes would not 
have any adverse effect on the operation of the rudder control system. 
However, this new system will provide significant benefits in the 
capability to detect certain failures, provide crew annunciation, and 
activate the standby rudder PCU. When the standby rudder PCU is 
activated along with the main rudder PCU, there will be effectively 
three PCUs controlling the rudder surface position.
    In light of this information and based on our certification 
activities, the new rudder control system will adequately address the 
identified unsafe condition. No change to the final rule is necessary 
in this regard.

Suggestion Regarding the Identified Unsafe Condition

    One commenter suggested that electromagnetic interference may have 
contributed to reported events of uncommanded rudder movement on Boeing 
Model 737-100, -200, -300, -400, and -500 series airplanes. However, 
the commenter concluded that, if this is true, those airplanes have 
already been fixed by previously mandated changes to the yaw damper 
system.
    We do not concur with the commenter's suggestion or conclusion. The 
only electrical components in the rudder control system are in the yaw 
damper system. The existing rudder yaw damper system has mechanical 
stops that limit rudder movement to the yaw damper authority. In a 
normally functioning system, it is not possible for electrical 
interference to move the rudder beyond the mechanical stops. No change 
to the final rule is necessary in this regard.

Requests To Revise the Compliance Time

    Several commenters request revising the proposed compliance time of 
5 years, and two commenters suggest a new compliance time of September 
2008. In addition, several commenters recommend basing the compliance 
time on the completion of tests for the new main rudder PCU, receipt of 
service bulletins, operators' maintenance schedules, and parts 
availability. Additional recommendations and FAA responses are 
described as follows:
    [sbull] One commenter states that wiring kits should be available 
in the second quarter of 2002, but actual hardware won't be available 
until the year 2003. In addition, because of the number of affected 
airplanes (about 150) in the commenter's fleet, the proposed 5-year 
compliance time will not be sufficient to accomplish the required 
actions if receipt of the service bulletins and parts are delayed for 2 
years.
    [sbull] One commenter suggests extending the compliance time to 10 
years, and states that the extensive modifications required by the 
proposed rule are best suited for accomplishment at a D-check.
    [sbull] One commenter is concerned about parts availability and a 
possible schedule slide. The commenter states that the manufacturer 
projects a maximum production capacity of 100 PCUs per month, with 
about 75 of those units available for retrofit each month after 
airplane production line requirements are met. In addition, if PCU 
certification and production proceed on schedule, a maximum of 3,300 
airplanes could be retrofitted within 44 months, which would be 
insufficient to meet 27 percent of potential worldwide demands. The 
commenter is concerned that, if PCU certification or the production 
schedule should slide, the schedule for providing sufficient parts 
would be adversely affected.
    [sbull] One commenter, the manufacturer, justifies its request for 
a September 2008 compliance time by noting the benefits of a slower 
introduction to the retrofit program. The manufacturer states that the 
FAA made assumptions in the proposed AD based on estimates for 
retrofitting U.S.-registered airplanes (about 2,000). However, the 
manufacturer notes that it must plan for retrofitting the worldwide 
fleet (about

[[Page 62345]]

4,500 airplanes). In addition, because the proposed changes to the 
rudder control system will require modifications throughout the 
airplane, the manufacturer recommends the September 2008 compliance 
time to allow for a phased approach for the retrofit program, thereby 
providing the time necessary to correct any issues identified during 
the first retrofits.
    We partially concur with the commenters' requests to revise the 
compliance time. We have considered the commenters' suggestions and 
concerns, and have made the following determinations. We concur with 
the requests to revise the compliance time to the year 2008, but do not 
concur with the request to extend the compliance time to 10 years. We 
agree that the 5-year compliance time required by the proposed rule may 
not allow operators sufficient time to accomplish the required design 
modifications. We also agree that the new compliance time should take 
into consideration when the service bulletins will be issued and when 
the required parts will be made available to the operators.
    In addressing the concerns about delays in the issuance of service 
bulletins, insufficient parts, and sliding schedules, the manufacturer 
has established a firm schedule and has assured us that all service 
information and parts will be provided within the required 6-year 
compliance time to support the new rudder control system. The 
manufacturer also has established backup plans to further ensure that 
parts will be available to meet schedule deadlines. To date, the 
manufacturer has informed us that the necessary service information is 
being developed and will be issued according to schedule, and that all 
necessary parts are being manufactured and will be available per the 
schedule. Further, we will closely monitor the manufacturer's schedule 
to ensure that all service information and parts are provided to the 
operators on time.
    In making our determination to extend the compliance time from 5 to 
6 years, we also have taken into consideration the service record of 
Model 737 series airplanes since the accomplishment of the 
modifications required by AD 97-14-03 and AD 97-14-04. In light of all 
of this information, we have determined that a compliance time of 6 
years will provide sufficient time for affected operators to install 
the new rudder control system without adversely affecting safety. 
Paragraph (a) of the final rule is revised accordingly.

Requests To Delay Issuance of Proposed Rule

    Although several commenters support the intent of the proposed AD, 
the commenters request delaying issuance of the proposed rule. The 
specific comments are described as follows:
    [sbull] The Air Transport Association (ATA) of America, on behalf 
of some of its members, recommends delaying issuance of the proposed 
rule until after the new main rudder PCU is tested and certified, and 
after the service information is issued by the manufacturer and 
approved by the FAA. Although service bulletins for the wiring 
installations for certain airplanes were issued in February 2002, 
issuance of additional service bulletins are not expected until the 
third quarter of 2002. In addition, service information for PCU 
procedures is not expected until July 2003. ATA is concerned about the 
risks associated with mandating the proposed actions before completing 
test and evaluation procedures for the new rudder control system, and 
about the limited number of retrofit kits that will be available each 
month.
    [sbull] One commenter strongly recommends waiting to issue the 
proposed rule until the relevant Boeing service bulletins and required 
parts are available. As noted earlier in the ``Requests to Revise the 
Compliance Time'' paragraph of this AD, that same commenter stated 
that, although the wiring kits would be available in the second quarter 
of 2002, actual hardware would not be available until the year 2003.
    [sbull] Two commenters consider that the proposed rule should be 
issued after the new rudder control system has been tested and 
approved. Issuing the proposed rule before approval of the system does 
not allow operators the opportunity to evaluate and comment on the 
system. Requiring installation of an unknown system places an undue 
burden on operators, since procedures for the corrective action are not 
yet defined.
    We do not agree that issuance of this AD should be delayed. The 
manufacturer has assured us that the compliance time specified by this 
AD will allow sufficient time to design, test, and evaluate the new 
rudder control system. As described earlier, we are monitoring the 
manufacturer's schedule for issuing the required service information 
and providing parts, and we will strive to ensure that the parts and 
information will be provided to the operators so that they can meet the 
requirements of this AD.
    We infer from the commenters' requests to delay issuance of the 
final rule that the commenters are seeking more time to comply with the 
rule. In this regard, we partially concur, and, as described earlier in 
this AD, have extended the 5-year compliance time specified in the 
proposed AD to 6 years. The manufacturer has assured us that, in 
addition to the wiring service information issued in February 2002, it 
will provide all additional service information (including PCU 
procedures) and parts necessary to meet the requirements of this AD. In 
addition, the new rudder control system, including all necessary 
components for the system, will be thoroughly tested and evaluated 
prior to issuance of the service information. No change is made to the 
final rule in this regard. As described earlier, paragraph (a) of the 
final rule specifies the new compliance time of 6 years after the 
effective date of this AD.

Cost Concerns

    One commenter states that the proposed costs are substantial 
($184,000 per airplane, or $364 million for U.S. operators).
    We recognize that the costs for the new rudder control system are 
substantial. However, in determining the costs associated with the new 
rudder control system, we based our cost estimate on the manufacturer's 
estimate of 700 work hours per airplane for the installation of the new 
rudder control system, and our estimate of approximately $140,000 per 
airplane for parts. For reasons specified in the proposed AD, we have 
determined that an unsafe condition exists, and we consider that 
accomplishment of the requirements of this AD is necessary to address 
that identified unsafe condition. No change is made to the final rule 
in this regard.

Request To Supersede Certain ADs

    One commenter considers that any new proposed rule should supersede 
the ADs listed in the following table and described below:

                               Commenter's Suggested List of ADs To Be Superseded
----------------------------------------------------------------------------------------------------------------
                                              Amendment
                  AD No.                         No.                     Federal Register citation
----------------------------------------------------------------------------------------------------------------
95-06-53..................................  39-9199       60 FR 18981, April 14, 1995.
97-05-10..................................  39-9954       62 FR 9679, March 4, 1997.

[[Page 62346]]

 
97-06-09..................................  39-9966       62 FR 12739, March 18, 1997.
97-09-14*.................................  39-10010      62 FR 24008, May 2, 1997.
97-09-15*.................................  39-10011      62 FR 24325, May 5, 1997.
97-14-03..................................  39-10060      62 FR 34623, June 27, 1997.
97-14-04..................................  39-10061      62 FR 35068, June 30, 1997.
98-02-01..................................  39-10283      63 FR 1903, January 13, 1998.
99-11-05*.................................  39-11175      64 FR 27905, May 24, 1999.
2000-22-02 R1.............................  39-11948      65 FR 69239, November 16, 2000.
----------------------------------------------------------------------------------------------------------------

    [sbull] Asterisks in the preceding table indicate the following 
changes since the issuance of those ADs:
    [sbull] AD 97-09-14 was superseded by AD 2000-02-18, amendment 39-
11536 (65 FR 5238, February 3, 2000).
    [sbull] AD 97-09-15 was revised by AD 97-09-15 R1, amendment 39-
10912 (63 FR 64857, November 24, 1998).
    [sbull] AD 99-11-05 was corrected by AD 99-11-05 COR, amendment 39-
11175 (64 FR 27905, May 24, 1999).
    The commenter adds that incidents of uncommanded rudder movement 
were reported on airplanes prior to the accomplishment of AD 97-14-03 
and AD 97-14-04; however, no incidents have occurred since the 
accomplishment of those ADs. In addition, the manufacturer of the main 
rudder PCU has accomplished 361 displacement tests per AD 99-11-05, and 
no discrepancies occurred during those tests.
    We partially concur with the commenter's request. We have 
determined that the final rule should supersede the two ADs cited in 
the NPRM (AD 97-14-04 and AD 2000-22-02 R1) and only five of the ADs 
listed in the table above (AD 95-06-53, 97-05-10, 97-09-15 R1, 98-02-
01, and 99-11-05 COR). (Those five ADs were described in detail in this 
AD in ``Actions Since Issuance of Proposed Rule.'')
    However, we do not agree that this AD should supersede AD 97-06-09, 
AD 97-14-03, or AD 2000-02-18 (which supersedes 97-09-14) because the 
requirements of those ADs are necessary to correct unsafe conditions 
that are not addressed by the requirements of this AD. In addition, the 
components and system specified in AD 97-14-03 are compatible with the 
new rudder control system and are necessary for the operation of that 
system. The requirements of those three ADs are described as follows:
    [sbull] AD 97-06-09, applicable to certain Boeing Model 737-300, -
400, and -500 series airplanes, requires replacing certain aileron/
rudder trim control modules with an improved module that contains an 
improved rudder trim switch that precludes the problems of sticking 
associated with the existing switch. That AD is intended to prevent 
such sticking.
    [sbull] AD 97-14-03, applicable to all Boeing Model 737-100, -200, 
-300, -400, and -500 series airplanes, requires installation of a newly 
designed rudder-limiting device and yaw damper system. As described 
earlier in this AD in the ``Actions Since Issuance of Proposed Rule'' 
paragraph, AD 97-14-03 supersedes AD 98-02-01 (which requires 
mechanical rate gyroscopes that are no longer approved for installation 
on Model 737 series airplanes). The new yaw damper system required by 
AD 97-14-03 is intended to prevent excessive rudder authority and 
consequent reduced controllability of the airplane, and malfunctions of 
the yaw damper system.
    [sbull] AD 2000-02-18 (which supersedes AD 97-09-14), applicable to 
certain Boeing Model 737-100, -200, -300, -400, and -500 series 
airplanes, requires an inspection of reworked aileron/elevator PCUs and 
rudder PCUs to determine if reworked PCU manifold cylinder bores 
containing chrome plating are installed, and replacement of the 
cylinder bores with cylinder bores that have been reworked using the 
oversize method or the steel sleeve method if necessary. That AD is 
intended to prevent a reduced rate of movement of the elevator, 
aileron, or rudder due to contamination of hydraulic fluid from chrome 
plating chips. Such reduced rate of movement, if not corrected, could 
result in reduced controllability of the airplane.
    We have revised the final rule to supersede the five ADs listed and 
described in a previous paragraph, ``Actions Since Issuance of Proposed 
Rule.'' As discussed previously in this AD, the final rule also 
supersedes two other ADs.

Conclusion

    After careful review of the available data, including the comments 
noted above, we have determined that air safety and the public interest 
require the adoption of the rule with the changes previously described. 
We also have determined that these changes will neither increase the 
economic burden on any operator nor increase the scope of the AD.

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 will be affected by this AD.
    The new installation action that is required by this new AD will 
take approximately 700 work hours per airplane to accomplish, at an 
average labor rate of $60 per work hour. Required parts will cost 
approximately $140,000 per airplane. Based on these figures, the cost 
impact of the new requirements of this AD on U.S. operators is 
estimated to be $364,000,000 (over the proposed 6-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 requirements of this AD 
action, and that no operator would accomplish those actions 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.

Regulatory Impact

    The regulations adopted herein will 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 final rule does not have federalism 
implications under Executive Order 13132.

[[Page 62347]]

    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under DOT Regulatory Policies and 
Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action 
and it is contained in the Rules Docket. A copy of it may be obtained 
from 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.

Adoption of the Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration amends 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 39-9199 (60 FR 
18981, April 14, 1995); amendment 39-9954 (62 FR 9679, March 4, 1997); 
amendment 39-10061 (62 FR 35068, June 30, 1997); amendment 39-10283 (63 
FR 1903, January 13, 1998); amendment 39-10912 (63 FR 64857, November 
24, 1998); amendment 39-11175 (64 FR 27905, May 24, 1999); and 
amendment 39-11948 (65 FR 69239, November 16, 2000); and by adding a 
new airworthiness directive (AD), amendment 39-12903, to read as 
follows:

2002-20-07 Boeing: Amendment 39-12903. Docket 2001-NM-251-AD. 
Supersedes AD 95-06-53, Amendment 39-9199; AD 97-05-10, Amendment 
39-9954; AD 97-09-15 R1, Amendment 39-10912; AD 97-14-04, Amendment 
39-10061; AD 98-02-01, Amendment 39-10283; AD 99-11-05 COR, 
Amendment 39-11175; 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 6 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 also will 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 the ADs listed in the following table, are not 
considered to be approved as alternative methods of compliance with 
this AD:

                           Table--List of ADs
------------------------------------------------------------------------
                                                              Amendment
                          AD No.                                 No.
------------------------------------------------------------------------
95-06-53..................................................  39-9199
97-05-10..................................................  39-9954
97-09-15 R1...............................................  39-10912
97-14-04..................................................  39-10061
98-02-01..................................................  39-10283
99-11-05 COR..............................................  39-11175
2000-22-02 R1.............................................  39-11948
------------------------------------------------------------------------


    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.

Effective Date

    (d) This amendment becomes effective on November 12, 2002.

    Issued in Renton, Washington, on September 27, 2002.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 02-25346 Filed 10-4-02; 8:45 am]
BILLING CODE 4910-13-P