[Federal Register Volume 63, Number 199 (Thursday, October 15, 1998)]
[Proposed Rules]
[Pages 55343-55345]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-27603]


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 Proposed Rules
                                                 Federal Register
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
 
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 

  Federal Register / Vol. 63, No. 199 / Thursday, October 15, 1998 / 
Proposed Rules  

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-258-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-600, -700, and -800 
Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-600, -
700, and -800 series airplanes. This proposal would require repetitive 
inspections to detect damage of the aft strut insulation blanket. This 
proposal also would require eventual replacement of the insulation 
blankets with new, improved blankets, which would constitute 
terminating action for the requirements of this AD. This proposal is 
prompted by reports of damaged aft strut insulation blankets. The 
actions specified by the proposed AD are intended to prevent such 
damage, which could result in exposure of the lower surface of the 
strut to extreme high temperatures, consequent creation of a source of 
fuel ignition, and increased risk of a fuel tank explosion and fire.

DATES: Comments must be received by November 30, 1998.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-258-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except 
Federal holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Bernie Gonzalez, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2682; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 98-NM-258-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 98-NM-258-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports indicating that during an evaluation 
of the aft strut insulation blankets that were installed on three 
Boeing Model 737 series flight test airplanes, cracks were found in the 
face sheets of the insulation blankets. Inspections on five in-service 
airplanes revealed two additional airplanes with such cracked 
insulation blankets. At the time these damaged insulation blankets were 
detected, the two in-service airplanes had accumulated 730 flight hours 
and 946 flight hours, respectively. Damage of these insulation 
blankets, which are located between the engine exhaust nozzle and the 
underside of the aft compartment of the engine strut, could cause the 
temperature on the bottom of that compartment to exceed normal limits 
during engine operation. That compartment is located immediately below 
the wing fuel tank and contains hydraulic lines and components where 
fuel leaks may occur. Such damage, if not corrected, could result in 
exposure of the lower surface of the strut to extreme high 
temperatures, consequent creation of a source of fuel ignition, and 
increased risk of a fuel tank explosion and fire.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
737-54A1038, dated May 7, 1998, as revised by Notice of Status Change 
737-54A1038 NSC 01, dated June 18, 1998, which describes procedures for 
repetitive visual and borescope inspections to detect cracks in and/or 
separation of the face sheet of the aft strut insulation blanket. The 
alert service bulletin also describes procedures for replacement of the 
aft strut insulation blanket with a new, improved blanket, which would 
eliminate the need for the repetitive inspections. Accomplishment of 
the actions specified in the alert service bulletin is intended to 
adequately address the identified unsafe condition.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require accomplishment of the actions

[[Page 55344]]

specified in the alert service bulletin described previously, except as 
discussed below.

Differences Between Proposed Rule and Alert Service Bulletin

    Operators should note that this AD proposes to mandate, within 18 
months, the replacement of the aft strut insulation blankets that is 
described in Boeing Alert Service Bulletin 737-54A1038, as revised by 
Notice of Status Change 737-54A1038 NSC 01, as terminating action for 
the repetitive inspections.
    The FAA has determined that long-term continued operational safety 
will be better assured by design changes to remove the source of the 
problem, rather than by repetitive inspections. Long-term inspections 
may not be providing the degree of safety assurance necessary for the 
transport airplane fleet. This, coupled with a better understanding of 
the human factors associated with numerous continual inspections, has 
led the FAA to consider placing less emphasis on inspections and more 
emphasis on design improvements. The proposed replacement requirement 
is in consonance with these conditions.

Cost Impact

    There are approximately 33 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 26 airplanes of U.S. registry 
would be affected by this proposed AD.
    It would take approximately 1 work hour per airplane to accomplish 
the proposed inspection, at an average labor rate of $60 per work hour. 
Based on these figures, the cost impact of the inspection proposed by 
this AD on U.S. operators is estimated to be $1,560, or $60 per 
airplane, per inspection cycle.
    It would take approximately 1 work hour per airplane to accomplish 
the proposed replacement, at an average labor rate of $60 per work 
hour. Required parts would be provided by the manufacturer at no cost 
to the operators. Based on these figures, the cost impact of the 
replacement proposed by this AD on U.S. operators is estimated to be 
$1,560, or $60 per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:
    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

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

Boeing: Docket 98-NM-258-AD.

    Applicability: Model 737-600, -700, and -800 series airplanes, 
line numbers 1 through 64 inclusive, 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 (d) 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 damage of the aft strut insulation blankets, which 
could result in exposure of the lower surface of the strut to 
extreme high temperatures, consequent creation of a source of fuel 
ignition, and increased risk of a fuel tank explosion and fire, 
accomplish the following:
    (a) Within 500 flight hours since date of manufacture of the 
airplane, or within 30 days after the effective date of this AD, 
whichever occurs later, perform a visual or borescope inspection to 
detect damage (cracks greater than 2.00 inches and/or separation of 
the face sheet) of the aft strut insulation blanket, part number (P/
N) S315A213-42, in accordance with Boeing Alert Service Bulletin 
737-54A1038, dated May 7, 1998, as revised by Notice of Status 
Change 737-54A1038 NSC 01, dated June 18, 1998. Thereafter, repeat 
the visual or borescope inspection at intervals not to exceed 250 
flight hours.
    (b) If damage (cracks greater than 2.00 inches and/or separation 
of the face sheet) of any aft strut insulation blanket is detected 
during any inspection required by paragraph (a) of this AD, prior to 
further flight, accomplish either paragraph (b)(1) or (b)(2) of this 
AD.
    (1) Replace any damaged insulation blanket having P/N S315A213-
42 with a new insulation blanket having P/N S315A213-42, in 
accordance with Boeing Alert Service Bulletin 737-54A1038, dated May 
7, 1998, as revised by Notice of Status Change 737-54A1038 NSC 01, 
dated June 18, 1998. Thereafter, repeat the visual or borescope 
inspection required by paragraph (a) of this AD at intervals not to 
exceed 250 flight hours. Or
    (2) Replace any damaged insulation blanket having P/N S315A213-
42 with a new, improved insulation blanket having P/N S315A213-47, 
in accordance with Boeing Alert Service Bulletin 737-54A1038, dated 
May 7, 1998, as revised by Notice of Status Change 737-54A1038 NSC 
01, dated June 18, 1998. Accomplishment of this replacement 
constitutes terminating action for the repetitive inspection 
requirements of this AD.
    (c) Within 18 months after the effective date of this AD, 
replace any aft strut insulation blanket having P/N S315A213-42 with 
a new, improved insulation blanket having P/N S315A213-47, in 
accordance with Boeing Alert Service Bulletin 737-54A1038, dated May 
7, 1998, as revised by Notice of Status Change 737-54A1038 NSC 01, 
dated June 18, 1998. Accomplishment of this replacement constitutes 
terminating action for the requirements of this AD.
    (d) 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.


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

    (e) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on October 5, 1998.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-27603 Filed 10-14-98; 8:45 am]
BILLING CODE 4910-13-U