[Federal Register Volume 76, Number 75 (Tuesday, April 19, 2011)]
[Proposed Rules]
[Pages 21815-21820]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2011-9410]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2008-0415; Directorate Identifier 2007-NM-256-AD]
RIN 2120-AA64


Airworthiness Directives; The Boeing Company Model 737 Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Supplemental notice of proposed rulemaking (NPRM); reopening of 
comment period.

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SUMMARY: We are revising an earlier proposed airworthiness directive 
(AD) for certain Model 737 airplanes. The original NPRM would have 
required repetitive inspections, lubrications, and repetitive repairs/
overhauls of the ball nut and ballscrew and attachment (Gimbal) 
fittings for the trim actuator of the horizontal stabilizer; various 
installation(s); and corrective actions if necessary; as applicable. 
The original NPRM resulted from a report of extensive corrosion of a 
ballscrew used in the drive mechanism of the horizontal stabilizer trim 
actuator (HSTA). This action revises the original NPRM by adding 
airplanes to the applicability. We are proposing this supplemental NPRM 
to prevent an undetected failure of the primary load path for the 
ballscrew in the drive mechanism of the HSTA and subsequent wear and 
failure of the secondary load path, which could lead to loss of control 
of the horizontal stabilizer and consequent loss of control of the 
airplane.

DATES: We must receive comments on this supplemental NPRM by May 16, 
2011.

ADDRESSES: You may send comments by any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
     Fax: 202-493-2251.
     Mail: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue, SE., Washington, DC 20590.
     Hand Delivery: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
    For service information identified in this proposed AD, contact 
Boeing Commercial Airplanes, Attention: Data & Services Management, 
P.O. Box 3707, MC 2H-65, Seattle, Washington 98124-2207; telephone 206-
544-5000, extension 1, fax 206-766-5680; e-mail [email protected]; 
Internet https://www.myboeingfleet.com. You may review copies of the 
referenced service information at the FAA, Transport Airplane 
Directorate, 1601 Lind Avenue, SW., Renton, Washington. For information 
on the availability of this material at the FAA, call 425-227-1221.

Examining the AD Docket

    You may examine the AD docket on the Internet at http://www.regulations.gov; or in person at the Docket Management Facility 
between 9 a.m. and 5 p.m., Monday through Friday, except Federal 
holidays. The AD docket contains this proposed AD, the regulatory 
evaluation, any comments received, and other information. The street 
address for the Docket Office (telephone 800-647-5527) is in the 
ADDRESSES section. Comments will be available in the AD docket shortly 
after receipt.

FOR FURTHER INFORMATION CONTACT: Kelly McGuckin, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-
3356; telephone (425) 917-6490; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION: 

Comments Invited

    We invite you to send any written relevant data, views, or 
arguments about this proposed AD. Send your comments to an address 
listed under the ADDRESSES section. Include ``Docket No. FAA-2008-0415; 
Directorate Identifier 2007-NM-256-AD'' at the beginning of your 
comments. We specifically invite comments on the overall regulatory, 
economic, environmental, and energy aspects of this proposed AD. We 
will consider all comments received by the closing date and may amend 
this proposed AD because of those comments.
    We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We 
will also post a report summarizing each substantive verbal contact we 
receive about this proposed AD.

Discussion

    We issued a notice of proposed rulemaking (NPRM) (the ``original 
NPRM'') to amend 14 CFR part 39 to include an airworthiness directive 
(AD) that would apply to certain Boeing Model 737 airplanes. That 
original NPRM was published in the Federal Register on April 28, 2008 
(73 FR 22840). That original NPRM proposed to require repetitive 
inspections, lubrications, and repetitive repairs/overhauls of the ball 
nut and ballscrew and attachment (Gimbal) fittings for the trim 
actuator of the horizontal stabilizer; various installation(s); and 
corrective actions if necessary; as applicable.
    That original NPRM resulted from a report of extensive corrosion of 
a ballscrew used in the drive mechanism

[[Page 21816]]

of the horizontal stabilizer trim actuator (HSTA) on a Model 757 
airplane. Extensive corrosion of the primary load path ball bearings in 
the ballscrew assembly, if not corrected, could result in an undetected 
failure of the primary load path for the ballscrew in the drive 
mechanism of the HSTA and subsequent wear and failure of the secondary 
load path, which could lead to loss of control of the horizontal 
stabilizer and consequent loss of control of the airplane.
    The ballscrew assembly on Model 757 airplanes is similar to those 
on the affected Model 737 airplanes. Therefore, all of these models may 
be subject to the same unsafe condition.

Other Relevant Rulemaking

    We are considering additional rulemaking to address the identified 
unsafe condition on Model 757 airplanes.

Relevant Service Information

    We have reviewed Boeing Alert Service Bulletins 737-27A1277, 
Revision 2, dated January 8, 2010 (for Model 737-600, -700, -700C, -
800, -900, and -900ER series airplanes); and 737-27A1278, Revision 1, 
dated January 7, 2010 (for Model 737-100, -200, -200C, -300, -400, and 
-500 series airplanes). Boeing Alert Service Bulletins 737-27A1277, 
Revision 1, dated July 25, 2007; and 737-27A1278, dated May 24, 2007; 
were referred to in the original NPRM as the appropriate sources of 
service information for accomplishing the proposed actions. The 
revisions of the service information incorporate the following changes:
     Boeing Alert Service Bulletin 737-27A1277, Revision 2, 
dated January 8, 2010, adds Model 737-900ER airplanes to Group 2 of the 
effectivity, clarifies certain inspections necessary in Work Packages 1 
and 2, and contains certain editorial changes.
     Boeing Alert Service Bulletin 737-27A1278, Revision 1, 
dated January 7, 2010, corrects the work instructions for the 
horizontal stabilizer trim actuator (HSTA) name plate identification 
information in Work Package 4 and clarifies certain inspections 
necessary in Work Packages 1 and 2 and contains certain editorial 
changes. In addition, the Horizontal Stabilizer Gearbox End Play Test 
is added because the gearbox backlash inspection is only identified in 
the airplane maintenance manual for Model 737-600, -700, -800, and -900 
airplanes, but is also applicable to Model 737-100, -200, -300, -400, 
and -500 airplanes.

Actions Since Issuance of Original NPRM

    Since we issued the original NPRM, we have changed this 
supplemental NPRM to include the revised service information, which 
expands the applicability of the original NPRM. We have also revised 
paragraph (h) of the original NPRM (paragraph (g) of the supplemental 
NPRM) to include credit for actions accomplished before the effective 
date of the AD in accordance with previous revisions of the service 
information.

Comments

    We have considered the following comments on the original NPRM.

Request To Change Applicability

    Boeing asked that we revise the applicability in the original NPRM 
to specify that it applies to all Model 737 airplanes instead of 
listing the minor models associated with the referenced service 
information. Boeing stated that this would avoid possible supersedure 
of the AD or certification maintenance requirements on future type 
certification programs.
    We agree with the commenter for the reasons provided. We have 
changed paragraph (c) and the SUMMARY section of this supplemental NPRM 
to refer to all Model 737 airplanes.

Request To Clarify Procedures in Referenced Service Information

    Air Transport Association (ATA), on behalf of its member Air Tran 
Airways (Air Tran) stated that the referenced service information is 
very difficult to interpret and cites examples from the service 
information. Air Tran stated that the accomplishment instructions 
specified in the service information contain language that is not 
specific and can not be used to make definitive determinations with 
regard to serviceability. Air Tran cited an example in Section 
3.B.1.d.(2) of Boeing Alert Service Bulletin 737-27A1277, Revision 1, 
dated July 25, 2007, which specifies ``Large amounts of grease present 
* * *''. This language is not specific and open to a high degree of 
subjectivity. Air Tran added that other examples are in Section 
3.B.1.n.(1) of this service bulletin, which specifies ``majority of 
grease,'' and in several places in Figures 1 and 2 of this service 
bulletin. Air Tran notes that the work instructions in Section 3.B. of 
Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 
2007, do not exactly match the instructions provided with the figures. 
Air Tran stated that having two sets of work instructions makes if 
difficult to follow, and could result in missed or partially 
accomplished work steps. Air Tran adds that Section 3.B.1.d.(8)(c) of 
this service bulletin provides instructions to check for obvious 
differences in thread shape between thread grooves ``as given in CMM 
27-41-01.'' Air Tran noted that CMM 27-41-01 does not provide any 
procedure for checking for obvious differences. Air Tran also noted 
that the subject section should specify ``refer to'' rather than ``as 
given in.''
    Qantas has similar views to Air Tran and added that referring to 
the procedures specified by Air Tran for the on-wing inspection will be 
confusing to mechanics because the procedures are not designed to be 
completed on-wing. Qantas also suggested a better explanation and 
pictures be added to Section 3.B.1.n.(1) of Boeing Alert Service 
Bulletin 737-27A1277, Revision 1, dated July 25, 2007, to quantify what 
is normal and what is an indication of a failure. Qantas noted that 
where there is evidence of a grease seal starting to fail, but no 
metallic debris, replacement of the unit should be deferred for up to 
five days, this would ease the burden of excess airplane down time. 
Qantas also noted that Section 3.B.1(o) of the procedures is not 
specified in the requirement table in paragraph 1.E. of Boeing Alert 
Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007. Qantas 
suggested it be included in that paragraph. Qantas also asks that the 
detailed inspection criteria specified in Section 3.B.1.(d) of this 
service bulletin be clarified.
    We agree that the procedures in the referenced service information 
should be clarified. We asked Boeing to revise the subject service 
information to provide better guidance and further clarification of the 
tasks that are specified. Boeing revised the service information as 
requested, as noted under the ``Actions Since Original NPRM was 
Issued'' and ``Relevant Service Information,'' sections of this AD and 
further clarification of the procedures is provided in those revisions, 
as well as the deletion of unnecessary procedures. Some portions of the 
task descriptions were left open to allow operators some latitude in 
accomplishing the tasks. We have revised this AD to refer to the new 
service information.
    We agree that processes referred to by the commenters are not 
designed for on-wing or on-airplane inspections. Boeing provides 
clarification of the intent of these processes in Boeing Alert Service 
Bulletin 737-27A1277, Revision 2, dated January 8, 2010. Therefore, we 
have made no change to the

[[Page 21817]]

supplemental NPRM regarding this issue.
    Qantas also asked that Boeing Alert Service Bulletin 737-27A1277, 
Revision 1, dated July 25, 2007, be revised. Qantas stated that the 
footnote at the top of page 10 of that service bulletin specifies 
``Boeing recommends that operators continue to perform lubrication 
tasks for the Stabilizer Trim Actuator given in Maintenance Planning 
Document (MPD) Section 1 and 737 AMM 12-22-41.'' Qantas added that the 
MPD task requires lubrication every 1,600 flight hours or 8 months, and 
paragraph 3.B.1., of Boeing Alert Service Bulletin 737-27A1277, 
Revision 1, dated July 25, 2007, specifies doing the same task every 
1,600 flight hours or 12 months. Qantas noted that the Boeing 737 MPD 
and service bulletin tasks should not both be required. Qantas stated 
that the FAA or Boeing should clarify the lubrication tasks specified 
in that service bulletin, so operators can take credit for doing the 
task in accordance with that service bulletin.
    We agree with the commenter. Boeing revised the service information 
specified in the ``Relevant Service Information'' and ``Actions Since 
Original NPRM was Issued'' sections of this supplemental NPRM. The 
referenced note has been removed and a new note added to Table 1 of 
paragraph 1.E., Compliance, of both service bulletins, specifying that 
accomplishing the lubrication task in Boeing Alert Service Bulletin 
737-27A1277 or 737-27A1278 meets the intent of the lubrication task in 
the associated MPD.

Clarify Difference in Compliance Time Intervals

    Boeing and US Airways asked that the compliance time interval 
specified in the original NPRM for the repetitive repair/overhaul be 
changed from 20,000 or 25,000 flight cycles to 20,000 or 24,000 flight 
hours (depending on airplane configuration) for Model 737-100, -200, -
300, -400, and -500 series airplanes. Boeing stated that Tables 1 and 2 
of Boeing Alert Service Bulletin 737-27A1278, dated May 24, 2007, 
specify the correct interval. Boeing adds that the subsection, 
Repetitive Repair/Overhaul, should be changed from ``and thereafter at 
intervals not to exceed 20,000 or 25,000 flight cycles * * *'' to ``and 
thereafter at intervals not to exceed 20,000 or 24,000 flight hours * * 
*'' US Airways reiterated the Boeing comment and recommends the 
difference be clarified.
    We agree that clarification is necessary. The repetitive interval 
referred to in the original NPRM is incorrect. The correct interval of 
20,000 flight hours or 24,000 flight hours (depending on airplane 
configuration) is specified in Boeing Alert Service Bulletin 737-
27A1278, Revision 1, dated January 7, 2010. We have clarified the 
compliance time in this supplemental NPRM by referring to Boeing Alert 
Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010.

Clarify Difference in Secondary Service Information Reference

    US Airways asked that the secondary service information referenced 
in Note 1 of the original NPRM be clarified. US Airways stated that 
Note 1 refers to Linear Motion Service Bulletin 7901708, Revision A, 
dated July 26, 2005; however, the service bulletin supplied to US 
Airways from Linear Motion specifies Revision B.
    We agree with the commenter. Since Revision B merely corrects a 
typographical error, Linear Motion Service Bulletin 7901708, Revisions 
A and B, both dated July 26, 2005, are acceptable. We have revised Note 
1 of this supplemental NPRM accordingly.

Request for Credit for Accomplishing Previously Issued Service 
Information

    US Airways referenced paragraph (h) of the original NPRM which 
specified ``Actions done before the effective date of this AD in 
accordance with Boeing Alert Service Bulletin 737-27A1277, dated July 
21, 2005, are acceptable for compliance with the corresponding 
requirements of this AD.'' US Airways asked that a similar paragraph be 
added to give credit for previous accomplishment of Boeing Alert 
Service Bulletin 737-27A1278, dated May 24, 2007.
    We agree with the commenter and have changed paragraph (g) of this 
supplemental NPRM to give credit for certain actions done in accordance 
with Boeing Alert Service Bulletin 737-27A1278, dated May 24, 2007.

Request To Clarify Compliance Times

    Boeing asked that an additional statement be added to the 
compliance time in paragraph (g) of the original NPRM to clarify that 
it is dependent on the airplane configuration defined in the referenced 
service information. Boeing stated that the multiple recommended 
compliance times may be confusing to operators as there is no 
distinction of dependence on airplane configuration for the initial 
compliance times. Boeing suggested clarifying the compliance time by 
adding ``(depending upon airplane configuration called out in the SB)'' 
in parenthesis.
    We agree with the commenter for the reasons provided. We have 
changed paragraph (g) of the supplemental NPRM to include the phrase 
``depending on airplane configuration'' in parenthesis following the 
compliance time reference.

Request To Use Continuous Maintenance Program/Move Maintenance Planning 
Document (MPD) Tasks to Referenced Service Information

    ATA on behalf of its member American Airlines reiterated the 
American Airlines comment that, except for accomplishing the 
installation of the strengthened ballnut retainers, all remaining 
requirements are part of the Model 737-800 continuous maintenance 
program and are subject to the type certification maintenance program 
rules. American Airlines stated that there are no historical 
indications for Model 737-NG airplanes that warrant an AD. American 
Airlines did not agree that the requirements in the AD that pertain to 
different airplane models with different designs and component 
manufacturers are strong enough to suspend parts of a continuous 
maintenance program. American Airlines added that if we have data not 
cited in the NPRM that substantiates an AD then the specified tasks 
should be removed from the continuous maintenance program. American 
Airlines concluded that continuous maintenance tasks such as inspection 
and lubrication typically have no terminating action by definition.
    Air Tran supported the requirement to accomplish the installation 
of the strengthened ballnut retainers, but also requested that we allow 
the use of maintenance tasks and states that the lubrication 
requirements of Boeing Alert Service Bulletin 737-27A1277, Revision 1, 
dated July 25, 2007, are similar to those in Boeing 737NG MPD Task 27-
102-00 and the inspection requirements are similar to those in Boeing 
737NG MPD Task 27-110-00. Air Tran added that the full requirements of 
Boeing 737NG MPD Tasks 27-102-00 and 27-110-00 should be incorporated 
into the AD and the subject MPD tasks removed from the Boeing 737NG MPD 
to avoid confusion. Qantas also asked that Boeing 737NG MPD Task 27-
110-00-1 be incorporated into Boeing Alert Service Bulletin 737-
27A1277, Revision 1, dated July 25, 2007. Qantas stated that if this 
task is included operators will not perform duplicate tasks from the 
Boeing 737NG MPD and referenced service information.
    We infer that ATA, American Airlines, Air Tran, and Qantas are

[[Page 21818]]

asking that the Boeing 737NG MPD Tasks specified in the original NPRM 
be removed, except for accomplishing the installation of the 
strengthened ballnut retainers, because all remaining requirements are 
part of the maintenance program. We do not agree with the commenters. 
We proposed mandating the maintenance tasks and intervals because of 
the criticality of maintaining the horizontal stabilizer control 
system; the consequences of not performing the maintenance tasks; and 
the service history attributed to lack of adequate horizontal 
stabilizer system maintenance on other airplanes. These maintenance 
actions can affect the safety of the airplane if they are not performed 
in a timely manner. We approve the maintenance review board report 
(MRBR), which is the basis for the MPD; the MRBR is an industry 
document that can only be changed by the MRB. The overlap is noted in 
Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 
2007, which identifies the MPD tasks. No revision to the MRBR is 
currently planned. Failure to perform the actions in this supplemental 
NPRM can lead to an unsafe condition; therefore, we have made no change 
to the supplemental NPRM in this regard.
    Sun Country Airlines (Sun Country) stated that operators may need 
clarification on whether or not ``restore,'' as identified in Boeing 
737NG MPD Item 27-108-00, meets the intent of the actions in the 
original NPRM. Sun Country stated that the repetitive actions specified 
in Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 
25, 2007, are closely related to Boeing 737NG MPD Items 27-102-00, 27-
108-00, and 27-110-00, in procedure as well as interval. Sun Country 
asked if operators following these MPD items can take credit for those 
already established maintenance requirements in lieu of the actions in 
the original NPRM. Sun Country added that because these MPD items 
already exist it would be advisable to change them to certification 
maintenance requirements (CMR) instead of mandating AD action.
    We agree that certain requirements in Boeing Alert Service Bulletin 
737-27A1277, Revision 1, dated July 25, 2007, are similar to those 
tasks in the Boeing 737NG MPD. Boeing revised the referenced service 
information to address this issue. A note was added to the compliance 
tables in the service information stating that accomplishing the 
lubrication task in the service information meets the intent of Boeing 
737NG MPD lubrication Task 27-102-00. We do not agree that the MPD 
Items should be changed to CMR requirements, because CMR requirements 
are established as part of the type certification of an airplane and 
are not initiated due to in-service issues. There are certain 
differences between the MPD tasks and the proposed requirements in the 
supplemental NPRM (e.g., inspections of the cable drum and electrical 
connector are not part of the actions specified in the referenced 
service information). We have made no change to the supplemental NPRM 
in this regard.

Request To Include Serial Numbers for Ballnut Tube Retainer Units

    ATA on behalf of its member Air Tran noted that the identification 
of multiple airplane groups creates some confusion regarding which 
ballnut tube retainer units need to be installed. Air Tran asked that 
the AD identify the specific serial numbers of the units requiring 
modification to ensure that all affected units are covered.
    We do not agree with the commenters. Operators can determine if the 
modification has been incorporated by verifying the part number on the 
component or doing a visual inspection of the ballscrew assembly. The 
proposed requirements in this supplemental NPRM prohibit the 
installation of affected unmodified ballscrews on certain airplanes. As 
standard practice, the airplane manufacturer addresses affected 
airplanes in the delivered condition in the effectivity of its service 
information. We have made no change to the supplemental NPRM in this 
regard.

Request To Review Paragraph 1.E. of the Referenced Service Information

    Qantas asked that we review whether the desired level of inspection 
will be achieved using the current Boeing 737 CMM. Qantas stated that 
paragraph 1.E. of Boeing Alert Service Bulletin 737-27A1277, Revision 
1, dated July 25, 2007, specifies an overhaul every 25,000 flight 
hours; Boeing 737 CMM 27-45-12 recommends the unit to be tested and 
disassembled only to the extent necessary to repair test failures. 
Qantas required vendors to strip the unit and complete visual and 
magnetic particle inspections.
    We do not agree with the commenter. The intervals and tasks 
necessary for the lubrication, detailed inspection and overhaul/repair 
of the HSTA described in Boeing Alert Service Bulletin 737-27A1277, 
Revision 2, dated January 8, 2010, and proposed in this supplemental 
NPRM, address the unsafe condition of an undetected failure of the 
ballscrew primary load path and subsequent wear and failure of the 
secondary load path for affected airplanes. Due to these factors, we 
have determined that the desired level of inspection will be achieved 
when performing an HSTA overhaul. We have made no change to the 
supplemental NPRM in this regard.

Request To Extend Overhaul Life Limit

    Qantas stated that by making the overhaul life limit mandatory the 
airline loses any flexibility in escalating the overhaul life based on 
service experience. Qantas added that there is considerable safety 
benefit in doing thorough overhauls with feedback of findings; one of 
the incentives for doing this is it includes the possibility of an 
overhaul life extension. Qantas noted that the original NPRM indicates 
an overhaul cost of $3,200; however, a recent procurement exercise by 
Qantas indicated the overhaul costs are about $18,000 per unit, not 
including any parts replacements. Qantas concluded that there is a 
considerable burden if extending the overhaul life is not permitted.
    We do not agree to extend the intervals for maintenance tasks based 
on the commenter's service experience. In consideration of the safety 
implications, we determined that the compliance time for the 
maintenance tasks, as proposed, represents an appropriate interval in 
which the overhaul can be done in a timely manner within the fleet, 
while still maintaining an adequate level of safety. Although we 
acknowledge that the overhaul cost may be higher, the estimate in this 
supplemental NPRM is limited only to the cost of actions actually 
required by the AD, and is based on an estimate from the airplane 
manufacturer of the labor hours and subsequent cost necessary to 
accomplish those tasks. Therefore, we have made no change to the 
supplemental NPRM is this regard.

FAA's Determination and Proposed Requirements of the Supplemental NPRM

    We are proposing this supplemental NPRM because we evaluated all 
pertinent information and determined an unsafe condition exists and is 
likely to exist or develop on other products of the same type design. 
Certain changes described above expand the scope of the original NPRM. 
As a result, we have determined that it is necessary to reopen the 
comment period to provide additional opportunity for the public to 
comment on this supplemental NPRM.

[[Page 21819]]

Explanation of Changes to This Supplemental NPRM

    We have added a new paragraph (d) to this supplemental NPRM to 
provide the Air Transport Association (ATA) of America subject code 27; 
flight controls. This code is added to make this supplemental NPRM 
parallel with other new AD actions. We have reidentified subsequent 
paragraphs accordingly.
    We have removed Table 1 of the NPRM from this supplemental NPRM. 
Instead, we have provided the full service bulletin citations 
throughout this supplemental NPRM.
    Since issuance of the original NPRM, we have increased the labor 
rate used in the Costs of Compliance from $80 per work-hour to $85 per 
work-hour. The Costs of Compliance information, below, reflects this 
increase in the specified hourly labor rate.

Costs of Compliance

    We estimate that this proposed AD would affect 1,641 airplanes of 
U.S. registry. The following table provides the estimated costs for 
U.S. operators to comply with this proposed AD.

                                                                     Estimated Costs
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                      Number of U.S.-
           Action \1\                    Work hours \1\          Average labor        Parts        Cost per product     registered      Fleet cost \1\
                                                                 rate per hour                            \1\            airplanes
--------------------------------------------------------------------------------------------------------------------------------------------------------
Detailed inspections............  2 or 4......................             $85  None............  $170 or $340, per            1,641  Between $278,970,
                                                                                                   inspection cycle.                   and $557,940 per
                                                                                                                                       inspection cycle.
Lubrications....................  1 or 3......................              85  None............  $85 or $255, per             1,641  Between $139,485,
                                                                                                   lubrication cycle.                  and $418,455 per
                                                                                                                                       lubrication
                                                                                                                                       cycle.
Repairs/overhauls...............  40..........................              85  None............  $3,400 per repair/           1,641  $5,579,400 per
                                                                                                   overhaul.                           repair/overhaul
                                                                                                                                       cycle.
Installations...................  Between 1 and 3.............              85  $2,200..........  Between $2,285 and           1,352  Between $3,089,320
                                                                                                   $2,455.                             and $3,319,160.
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Depending on airplane configuration.

    The number of work hours, as indicated above, is presented as if 
the accomplishment of the actions in this proposed AD is to be 
conducted as new ``stand alone'' actions. However, in actual practice, 
the lubrications, detailed inspections, and overhauls are currently 
being done as part of normal airplane maintenance. The repair can be 
done coincidentally or in combination with the normally scheduled HSTA 
and ballscrew overhaul. Therefore, the actual number of necessary 
additional work hours will be minimal in many instances. Additionally, 
any costs associated with special airplane scheduling will be minimal.
    We estimate the following costs to do any necessary repairs/
replacements that would be required based on the results of the 
proposed inspection. We have no way of determining the number of 
aircraft that might need these repairs/replacements:

                                               On-Condition Costs
----------------------------------------------------------------------------------------------------------------
                  Action                            Labor cost           Parts cost        Cost per product
----------------------------------------------------------------------------------------------------------------
Remove/replace HSTA......................  Between 3 and 8 work hours            $0  Between $418,455 and
                                            x $85 per hour = between                  $1,115,880.
                                            $255 and $680.
----------------------------------------------------------------------------------------------------------------

Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to 
issue rules on aviation safety. Subtitle I, section 106, describes the 
authority of the FAA Administrator. ``Subtitle VII: Aviation 
Programs,'' describes in more detail the scope of the Agency's 
authority.
    We are issuing this rulemaking under the authority described in 
``Subtitle VII, Part A, Subpart III, Section 44701: General 
requirements.'' Under that section, Congress charges the FAA with 
promoting safe flight of civil aircraft in air commerce by prescribing 
regulations for practices, methods, and procedures the Administrator 
finds necessary for safety in air commerce. This regulation is within 
the scope of that authority because it addresses an unsafe condition 
that is likely to exist or develop on products identified in this 
rulemaking action.

Regulatory Findings

    We determined that this proposed AD would not have federalism 
implications under Executive Order 13132. This proposed AD 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.
    For the reasons discussed above, I certify 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. 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.
    You can find our regulatory evaluation and the estimated costs of 
compliance in the AD Docket.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

[[Page 21820]]

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. The FAA amends Sec.  39.13 by adding the following new AD:

The Boeing Company: Docket No. FAA-2008-0415; Directorate Identifier 
2007-NM-256-AD.

Comments Due Date

    (a) We must receive comments by May 16, 2011.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to all Model 737 airplanes; certificated in 
any category.

Subject

    (d) Air Transport Association (ATA) of America Code 27: Flight 
controls.

Unsafe Condition

    (e) This AD results from a report of extensive corrosion of a 
ballscrew in the drive mechanism of the horizontal stabilizer trim 
actuator (HSTA). We are issuing this AD to prevent an undetected 
failure of the primary load path for the ballscrew in the drive 
mechanism of the HSTA and subsequent wear and failure of the 
secondary load path, which could lead to loss of control of the 
horizontal stabilizer and consequent loss of control of the 
airplane.

Compliance

    (f) You are responsible for having the actions required by this 
AD performed within the compliance times specified, unless the 
actions have already been done.

Inspections, Lubrications, Repairs/Overhauls, and Applicable Corrective 
Actions

    (g) At the applicable compliance time and repeat intervals 
listed in Tables 1 and 2 of paragraph 1.E., ``Compliance,'' of 
Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 
7, 2010; or Boeing Alert Service Bulletin 737-27A1277, Revision 2, 
dated January 8, 2010; as applicable (depending on airplane 
configuration): Do the inspections, lubrications, repairs/overhauls, 
installation(s), and applicable corrective actions, by accomplishing 
all the applicable actions specified in the Accomplishment 
Instructions of Boeing Alert Service Bulletin 737-27A1278, Revision 
1, dated January 7, 2010; or Boeing Alert Service Bulletin 737-
27A1277, Revision 2, dated January 8, 2010; as applicable; except as 
provided by paragraphs (g)(1) and (g)(2) of this AD.

    Note 1: Boeing Alert Service Bulletin 737-27A1278, Revision 1, 
dated January 7, 2010; refers to Umbra Cuscinetti Service Bulletin 
07322-27-01, dated December 21, 2004; Linear Motion Service Bulletin 
7901708, Revision A, or Revision B, both dated July 26, 2005; Boeing 
737 Service Bulletin 27-1046, Revision 1, dated April 5, 1974; and 
Skytronics Service Bulletin 93004, dated September 1, 2005; as 
applicable; as additional sources of service information for 
accomplishing the applicable specified actions.


    Note 2: Boeing Alert Service Bulletin 737-27A1277, Revision 2, 
dated January 8, 2010; refers to Umbra Cuscinetti Service Bulletin 
07322-27-01, dated December 21, 2004; as an additional source of 
service information for accomplishing the applicable specified 
actions.

    (1) Where paragraph 1.E., ``Compliance,'' of Boeing Alert 
Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010; or 
Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 
8, 2010; as applicable; specifies an initial compliance time for 
accomplishing the initial inspection, lubrication, or repair/
overhaul, this AD requires doing the applicable initial action(s) at 
the later of the times specified in paragraphs (g)(1)(i) and 
(g)(1)(ii) of this AD.
    (i) At the applicable compliance time specified in paragraph 
1.E, ``Compliance,'' of Boeing Alert Service Bulletin 737-27A1278, 
Revision 1, dated January 7, 2010; or Boeing Alert Service Bulletin 
737-27A1277, Revision 2, dated January 8, 2010; as applicable.
    (ii) Within the applicable compliance time specified in 
paragraph (g)(1)(ii)(A), (g)(1)(ii)(B), or (g)(1)(ii)(C) of this AD.
    (A) For the initial detailed inspection and lubrication: Within 
6 months after the effective date of this AD.
    (B) For the initial repair/overhaul: Within 12 months after the 
effective date of this AD.
    (C) For the installation(s): Within 12 months after the 
effective date of this AD.
    (2) Where Table 2 of paragraph 1.E., ``Compliance,'' of Boeing 
Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 
2010, specifies a compliance time of ``* * * within 25,000 Flight 
Hours since the latest horizontal stabilizer trim actuator (HSTA) 
Overhaul from the date of Revision 1 of this Service Bulletin * * 
*,'' this AD requires compliance within 25,000 flight hours since 
the last overhaul of the trim actuator of the horizontal stabilizer.

Credit for Actions Accomplished in Accordance With Previous Service 
Information

    (h) Actions accomplished before the effective date of this AD in 
accordance with Boeing Alert Service Bulletins 737-27A1277, Revision 
1, dated July 25, 2007; or 737-27A1278, dated May 24, 2007; as 
applicable; are considered acceptable for compliance with the 
corresponding actions specified in this AD.

Parts Installation

    (i) As of the effective date of this AD, no person may install a 
ballscrew assembly in the drive mechanism of the HSTA on any 
airplane, unless it has been inspected and modified, as applicable, 
in accordance with paragraph (g) of this AD.

Alternative Methods of Compliance (AMOCs)

    (j)(1) The Manager, Seattle Aircraft Certification Office (ACO), 
FAA, has the authority to approve AMOCs for this AD, if requested 
using the procedures found in 14 CFR 39.19. In accordance with 14 
CFR 39.19, send your request to your principal inspector or local 
Flight Standards District Office, as appropriate. If sending 
information directly to the manager of the ACO, send it to the 
attention of the person identified in the Related Information 
section of this AD. Information may be e-mailed to: [email protected].
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the local flight standards district office/certificate holding 
district office.
    (3) An AMOC that provides an acceptable level of safety may be 
used for any repair required by this AD if it is approved by the 
Boeing Commercial Airplanes Organization Designation Authorization 
(ODA) that has been authorized by the Manager, Seattle ACO to make 
those findings. For a repair method to be approved, the repair must 
meet the certification basis of the airplane.

Related Information

    (k) For more information about this AD, contact Kelly McGuckin, 
Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., 
Renton, Washington 98057-3356; telephone (425) 917-6490; fax (425) 
917-6590.

    Issued in Renton, Washington, on April 13, 2011.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2011-9410 Filed 4-18-11; 8:45 am]
BILLING CODE 4910-13-P