[Federal Register Volume 62, Number 31 (Friday, February 14, 1997)]
[Rules and Regulations]
[Pages 6861-6864]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-3267]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 96-NM-153-AD; Amendment 39-9925; AD 97-04-01]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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

SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 737 series airplanes, that requires 
modification of the aileron centering spring and trim mechanism. This 
amendment is prompted by a review of the design of the flight control 
systems on Model 737 series airplanes. The actions specified by this AD 
are intended to prevent jamming of the aileron control system during 
flight due to fracturing of the springs in the aileron centering units; 
this condition, if not corrected, could result in reduced lateral 
control of the airplane.

DATES: Effective March 21, 1997.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of March 21, 1997.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the Federal 
Aviation Administration (FAA), Transport Airplane Directorate, Rules 
Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of 
the Federal Register, 800 North Capitol Street, NW., Suite 700, 
Washington, DC.

FOR FURTHER INFORMATION CONTACT: Don Kurle, Senior Engineer, Systems 
and Equipment Branch, ANM-130S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (206) 227-2798; fax (206) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to certain Boeing Model 737 series 
airplanes was published in the Federal Register on August 28, 1996 (61 
FR 44247). That action proposed to require modification

[[Page 6862]]

of the aileron centering spring and trim mechanism.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

Request To Revise Statement of Findings of Critical Design Review 
Team

    One commenter requests the second paragraph of the Discussion 
section that appeared in the preamble to the proposed rule be revised 
to accurately reflect the findings of the Critical Design Review (CDR) 
team. The commenter asks that the FAA delete the one sentence in that 
paragraph, which read: ``The recommendations of the team include 
various changes to the design of the flight control systems of these 
airplanes, as well as correction of certain design deficiencies.'' The 
commenter suggests that the following sentences should be added: ``The 
team did not find any design issues that could lead to a definite cause 
of the accidents that gave rise to this effort. The recommendations of 
the team include various changes to the design of the flight control 
systems of these airplanes, as well as incorporation of certain design 
improvements in order to enhance its already acceptable level of 
safety.''
    The FAA does not find that a revision to this final rule in the 
manner suggested by the commenter is necessary, since the Discussion 
section of a proposed rule does not reappear in a final rule. The FAA 
acknowledges that the CDR team did not find any design issue that could 
lead to a definite cause of the accidents that gave rise to this 
effort. However, as a result of having conducted the CDR of the flight 
control systems on Boeing Model 737 series airplanes, the team 
indicated that there are a number of recommendations that should be 
addressed by the FAA for each of the various models of the Model 737. 
In reviewing these recommendations, the FAA has concluded that they 
address unsafe conditions that must be corrected through the issuance 
of AD's. Therefore, the FAA does not concur that these design changes 
merely ``enhance [the Model 737's] already acceptable level of 
safety.''

Request To Withdraw the Proposal

    One commenter contends that the proposal is not justified since it 
cannot be supported by data. The commenter does not consider that the 
proposal contributes to improving the safety aspects of Model 737 
airplanes. The commenter states that the Critical Design Review (CDR) 
team's report does not indicate that there is any evidence to tie the 
referenced service documents to any in-service problems or accidents. 
The commenter adds that the FAA has not indicated that it has reviewed 
any routine component tear-down reports that would support the proposed 
actions. The commenter concludes that the FAA does not understand the 
enormity of the proposed action. The FAA infers from these remarks that 
the commenter requests the proposed rule be withdrawn.
    The FAA does not concur. The FAA has received at least 26 reports 
from two operators of Model 737 series airplanes indicating that 
fractured springs were found in the aileron centering units. The cause 
of the fracturing was attributed to fatigue cracking. Two of the 
reports indicated that the fractured springs had become lodged in a 
centering cam hole, which caused binding of the aileron control system. 
The FAA's position is that this condition is a potential unsafe 
condition that must be corrected in order to ensure the safety of the 
affected fleet.

Request To Delay Issuance of the Final Rule

    The Air Transport Association (ATA) of America, on behalf of two of 
its members, requests that the FAA postpone issuing the final rule 
until Boeing revises the service bulletin cited in the proposal to 
incorporate the three Notice of Status Change documents referenced in 
the proposed AD. The ATA indicates that this will ensure no confusion 
exists concerning service bulletin recommendations.
    The FAA does not concur with the commenter's request to delay 
issuance of the final rule. The FAA has been advised that Boeing has no 
plans to revise the referenced service bulletin to incorporate the 
Notice of Status Change documents. To delay this action would be 
inappropriate, since the FAA has determined that an unsafe condition 
exists and that the required modification must be accomplished to 
ensure continued safety.

Requests To Revise Compliance Time

    One commenter requests that the proposed compliance time be 
shortened from 18 months to 12 months to provide an acceptable level of 
safety. The commenter provides no data in support of its request.
    A second commenter requests that the proposed compliance time be 
extended beyond 18 months to ensure that adequate parts and trained 
personnel are available to accomplish the modification. The commenter 
did not submit data to substantiate its request.
    The FAA does not concur with the commenters' requests to revise the 
compliance time. As explained in the preamble to the proposal, the 
FAA's intent is that the modification be performed during a regularly 
scheduled maintenance visit for the majority of the affected fleet when 
the airplanes would be located at a base where special equipment and 
trained personnel would be readily available, if necessary. The FAA 
finds that 18 months corresponds closely to the interval representative 
of most of the affected operators' normal maintenance schedules. The 
FAA considers that this interval will provide an acceptable level of 
safety.

Request To Allow Measurement of Thickness of Aileron Centering 
Spring

    The ATA, on behalf of one of its members, requests that operators 
be allowed to measure the thickness of the aileron centering spring in 
lieu of determining the part number. The ATA indicates that the part 
number of the aileron centering spring cannot be determined by 
inspecting the part because it is impossible to read the part number on 
the spring. However, the difference in diameter between the spring 
having part number 69-39429-2 and the spring having part number 69-
39429-3 can be distinguished by measurement. The ATA states that if a 
part has a thickness greater than 0.13 inch, this should constitute 
compliance with the AD. One ATA member indicates that drawings show 
that the spring having part number 69-39429-2 is made from 0.125-inch 
diameter wire, and that the spring having part number 69-39429-3 is 
made from 0.135-inch diameter wire.
    The FAA does not concur. The FAA acknowledges that, except for a 
removable tag, the spring is not marked with a part number. However, it 
is not necessary to read the part number of the spring. If an operator 
previously has performed the actions described in the referenced 
service bulletin, the correct spring should be installed on the 
airplane; if not, an incorrect spring would have been installed. In the 
unlikely event that the spring has been changed due to a maintenance 
action apart from incorporation of the referenced service bulletin, it 
is difficult to determine which spring is installed. The only way to 
ensure that the proper spring is installed is to perform the actions of 
the referenced service bulletin. Further, the FAA does not agree that 
the springs having part numbers 69-39429-2 and 69-39429-3 are made from 
different diameter wire;

[[Page 6863]]

the FAA has determined that both springs are made from 0.135-inch 
diameter wire.

Conclusion

    After careful review of the available data, including the comments 
noted above, the FAA has determined that air safety and the public 
interest require the adoption of the rule as proposed.

Cost Impact

    There are approximately 1,631 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 830 
airplanes of U.S. registry will be affected by this AD.
    The FAA estimates that 485 Group 1 airplanes will be affected by 
this AD. For Group 1 airplanes, the FAA estimates that it will take 
approximately 2 work hours per airplane to accomplish the required 
actions, and that the average labor rate is $60 per work hour. Required 
parts will cost approximately $707 per airplane. Based on these 
figures, the cost impact of the AD on U.S. operators of Group 1 
airplanes is estimated to be $401,095, or $827 per airplane.
    The FAA estimates that 345 Group 2 airplanes will be affected by 
this AD. For Group 2 airplanes, the FAA estimates that it will take 
approximately 2 work hours per airplane to accomplish the required 
actions, and that the average labor rate is $60 per work hour. Required 
parts will cost approximately $224 per airplane. Based on these 
figures, the cost impact of the AD on U.S. operators of Group 2 
airplanes is estimated to be $118,680, or $344 per airplane.
    The cost impact figures discussed above are 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.

Regulatory Impact

    The regulations adopted herein will not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    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, Incorporation by 
reference, 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 adding the following new 
airworthiness directive:

97-04-01  Boeing: Amendment 39-9925. Docket 96-NM-153-AD.

    Applicability: Model 737 series airplanes; as listed in Boeing 
Service Bulletin 737-27-1155, dated October 26, 1989; as revised by 
Notices of Status Change No. 737-27-1155NSC1, dated January 25, 
1990, No. 737-27-1155NSC2, dated February 15, 1990, and No. 737-27-
1155NSC3, dated May 17, 1990; certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (c) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent jamming of the aileron control system during flight, 
which could result in reduced lateral control of the airplane, 
accomplish the following:
    (a) Within 18 months after the effective date of this AD, 
accomplish the requirements of paragraphs (a)(1), (a)(2), and (a)(3) 
of this AD, as applicable, in accordance with Boeing Service 
Bulletin 737-27-1155, dated October 26, 1989; as revised by Notice 
of Status Change No. 737-27-1155NSC1, dated January 25, 1990, and 
Notice of Status Change No. 737-27-1155NSC2, dated February 15, 
1990, and Notice of Status Change No. 737-27-1155NSC3, dated May 17, 
1990.
    (1) For Groups 1 and 2 airplanes: Replace the aileron centering 
springs, part number (P/N) 69-39429-2, with improved springs, P/N 
69-39429-3, in accordance with the service bulletin and Notices of 
Status Change.
    (2) For Groups 1 and 2 airplanes: Install a two-piece plug, P/N 
69-78072-1, in the weight reduction hole in the feel cam in 
accordance with the service bulletin and Notices of Status Change.
    (3) For Group 1 airplanes: Replace the two eyebolts, P/N 69-
39423-1, of the aileron centering spring attachment with new 
eyebolts, P/N 69-74646-1, in accordance with the service bulletin 
and Notices of Status Change.
    (b) As of the effective date of this AD, no person shall install 
the items specified in paragraphs (b)(1) and (b)(2) of this AD on 
any airplane, as specified:
    (1) For Groups 1 and 2 airplanes: Aileron centering springs 
having P/N 69-39429-2 shall not be installed.
    (2) For Group 1 airplanes: Eyebolts, P/N 69-39423-1, of the 
aileron centering spring attachment shall not be installed.
    (c) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle Aircraft Certification 
Office (ACO), FAA, Transport Airplane Directorate. Operators shall 
submit their requests through an appropriate FAA Principal 
Maintenance Inspector, who may add comments and then send it to the 
Manager, Seattle ACO.

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

    (d) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.
    (e) The replacement and installation shall be done in accordance 
with Boeing Service Bulletin 737-27-1155, dated October 26, 1989; as 
revised by Notice of Status Change No. 737-27-1155NSC1, dated 
January 25, 1990, and Notice of Status Change No. 737-27-1155NSC2, 
dated February 15, 1990, and Notice of Status Change No. 737-27-
1155NSC3, dated May 17, 1990. This incorporation by reference was 
approved by the Director of the Federal Register in accordance with 
5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from 
Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 
98124-2207. Copies may be inspected at the FAA, Transport Airplane 
Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the 
Office of the Federal Register, 800 North Capitol Street, NW., suite 
700, Washington, DC.

[[Page 6864]]

    (f) This amendment becomes effective on March 21, 1997.

    Issued in Renton, Washington, on February 4, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-3267 Filed 2-13-97; 8:45 am]
BILLING CODE 4910-13-U