[Federal Register Volume 66, Number 84 (Tuesday, May 1, 2001)]
[Proposed Rules]
[Pages 21700-21703]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-10729]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-367-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737 series 
airplanes. This proposal would require initial and repetitive 
inspections of certain areas of the wing spars to detect cracking or 
corrosion; and follow-on corrective actions and repair, if necessary. 
This proposal is prompted by reports of cracks and corrosion in the 
upper chord of the front and rear spars of the wing and reports of 
cracks propagating from previously repaired areas. The actions 
specified in the proposed AD are intended to detect and correct such 
cracking or corrosion of the upper and lower chords of the wing spars, 
which could result in reduced structural integrity of the wing.

DATES: Comments must be received by June 15, 2001.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), ANM-114, Attention: Rules Docket No. 99-NM-367-
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. Comments may be submitted via 
fax to (425) 227-1232. Comments may also be sent via the Internet using 
the following address: [email protected]. Comments sent via fax 
or the Internet must contain ``Docket No. 99-NM-367-AD'' in the subject 
line and need not be submitted in triplicate. Comments sent via the 
Internet as attached electronic files must be formatted in Microsoft 
Word 97 for Windows or ASCII text.

[[Page 21701]]

    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: Nenita Odesa, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 
227-2557; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this action may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this action must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-367-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. 99-NM-367-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received numerous reports of cracking and corrosion in 
the upper chord of both the front and rear spars of the wing. Cracks 
were reported by 18 operators in the upper and rear spar chord on 38 
airplanes. In addition, 5 operators reported cracks propagating from 
repairs that were accomplished previously on 6 airplanes per Boeing 
Service Bulletin 737-57-1067, Revision 3, dated May 24, 1990, or 
earlier revisions. Findings indicate that 2 of those cracks were found 
in the front spar upper chord, and 4 cracks in the rear spar upper 
chord. Corrosion also was found in the external surfaces of the upper 
and lower chords of the front and rear spars on 64 airplanes. Such 
cracking and corrosion, if not corrected, could result in reduced 
structural integrity of the wing.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 737-57-
1067, Revision 4, dated November 7, 1991. Revision 4 adds initial and 
repetitive inspections for airplanes on which a previous repair to the 
upper chord of the front or rear spar was made per Revision 3, or 
earlier revisions, of the service bulletin. Revision 4 includes the 
following procedures:
     An initial (detailed) visual inspection for cracks of the 
external surfaces of the upper and lower chords of the front spar 
outboard of the engine nacelle, upper and lower chords of the rear 
spar, and the lower chord of the front spar inboard of the engine 
nacelle.
     An initial eddy current inspection for cracks of the 
external surfaces of the vertical legs of the upper chords of the front 
and rear spars.
     Repetitive close (detailed) visual inspections for cracks 
and corrosion of the external surfaces of the upper and lower chords of 
the front and rear spars.
     Repetitive eddy current inspections for cracks of the 
external surfaces of the vertical legs of the upper chords of the front 
and rear spars.
     Follow-on corrective actions that include cleaning the 
exposed front and rear spar cavities, removing corrosion by blending 
out the damaged surface areas, and applying a corrosion-inhibiting 
compound to the accessible areas of the upper and lower chords of the 
front and rear spars.
     Crack and corrosion repair that includes removing 
corrosion; inspecting the rework area for cracks, and repairing any 
cracks found in the specific chord surfaces of the front and rear 
spars, which includes installing a nesting angle if necessary and 
refinishing the blend out area; and applying a corrosion-inhibiting 
compound.

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

Differences Between Proposed Rule and Service Bulletin

    Operators should note that this proposed AD differs from the 
service bulletin in that it would NOT allow the following actions:
    1. Repair of certain damage (that exceeds the limits specified in 
the service bulletin) to be accomplished by contacting Boeing for 
repair instructions; rather, it would require that such repairs be 
accomplished per a method approved by the FAA.
    2. Flight with a horizontal crack in the upper chords of the front 
or rear spars; rather, it would require repair per a method approved by 
the FAA.
    3. ``Close visual inspections''; rather, it would require 
``detailed visual inspections.'' A note has been added following 
paragraph (a) of this proposed AD to clarify this.
    Operators also should note that Part II of the service bulletin 
does not include repair procedures if a horizontal crack is found in 
the upper chords of the front or rear spars. However, paragraph (d)(3) 
of this proposed AD requires repair of such cracking per a method 
approved by the FAA, as cited in paragraph (f) of this AD.
    Operators also should note that the service bulletin specifies 
initial detailed visual and eddy current inspections ``upon the 
accumulation of 20 years airframe age or within 1 year after receipt of 
Revision 3 of the service bulletin.'' However, since all airplanes in 
the applicability of this AD are over 20 years old, the FAA has 
determined that it is unnecessary to include the specification for the 
airframe age in this proposed AD.

Clarification of Action Required for Previous Repair

    The Accomplishment Instructions of the previously referenced 
service bulletin do not specifically include procedures for repetitive 
eddy current inspections for airplanes on which a previous repair to 
the upper chord of the front or rear spar was made per Boeing Service 
Bulletin 737-57-1067, Revision 3, or earlier revisions. However, such 
action is specified in the service bulletin in an ``Action'' paragraph 
of the Summary, and in paragraph C., ``Description.'' Paragraphs 
(d)(3), (d)(4)(ii), and (e) of this AD specify repair per a method 
approved by the FAA, which is cited in paragraph (f) of this AD.

[[Page 21702]]

Cost Impact

    There are approximately 168 Boeing Model 737 series airplanes of 
the affected design in the worldwide fleet. The FAA estimates that 45 
airplanes of U.S. registry would be affected by this proposed AD.
    The FAA estimates that it would take approximately 30 work hours 
per airplane to do the initial detailed visual and eddy current 
inspections, and that the average labor rate is $60 per work hour. 
Based on these figures, the cost impact of the initial inspections on 
U.S. operators is estimated to be $81,000, or $1,800 per airplane.
    The FAA estimates that it would take approximately 30 work hours 
per airplane to do the repetitive inspections, and that the average 
labor rate is $60 per work hour. Based on these figures, the cost 
impact of the proposed AD on U.S. operators is estimated to be $81,000, 
or $1,800 per airplane, per inspection cycle.
    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 do those actions in the 
future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would not have a substantial direct 
effect on the States, on the relationship between the national 
Government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, it 
is determined that this proposal would not have federalism implications 
under Executive Order 13132.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

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

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

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

Boeing:  Docket 99-NM-367-AD.

    Applicability: Model 737 series airplanes, line numbers 1 
through 310 inclusive, and 323; 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 per paragraph (g) 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 detect and correct cracking or corrosion of the upper and 
lower chords of the front and rear spars of the wing, which could 
result in reduced structural integrity of the wing, do the 
following:

Initial Detailed Visual and Eddy Current Inspections (Part I)

    (a) Within 12 months after the effective date of this AD: Do an 
initial detailed visual inspection to detect cracking or corrosion 
of the upper and lower chords of the front and rear spars, and an 
eddy current inspection to detect cracking of the vertical legs of 
the upper chords of the front and rear spars, per Part I of the 
Accomplishment Instructions of Boeing Service Bulletin 737-57-1067, 
Revision 4, dated November 7, 1991. Before further flight following 
the inspections, do the follow-on corrective actions required by 
paragraph (d) of this AD.

    Note 2: For the purposes of this AD, a detailed visual 
inspection is defined as: ``An intensive examination of a specific 
structural area, system, installation, or assembly to detect damage, 
failure, or irregularity. Available lighting is normally 
supplemented with a direct source of good lighting at an intensity 
deemed appropriate by the inspector. Inspection aids such as 
mirrors, magnifying lenses, etc. may be used. Surface cleaning and 
elaborate access procedures may be required.''

Repetitive Detailed Visual and Eddy Current Inspections (Part II)

    (b) Repeat the initial detailed visual inspection required by 
paragraph (a) of this AD at intervals not to exceed 12 months per 
Part II of the Accomplishment Instructions of Boeing Service 
Bulletin 737-57-1067, Revision 4, dated November 7, 1991. Before 
further flight following the inspection, do the follow-on corrective 
actions required by paragraph (d) of this AD.
    (c) Repeat the initial eddy current inspection required by 
paragraph (a) of this AD at intervals not to exceed 48 months per 
Part II of the Accomplishment Instructions of Boeing Service 
Bulletin 737-57-1067, Revision 4, dated November 7, 1991. Before 
further flight following the inspection, do the follow-on corrective 
actions required by paragraph (d) of this AD.

Follow-on Corrective Actions (Parts I, II, and III)

    (d) Do the follow-on corrective actions (including cleaning spar 
cavities, removing corrosion, and applying corrosion-inhibiting 
compound) required by paragraphs (d)(1), (d)(2), (d)(3), and (d)(4) 
of this AD, as applicable.
    (1) If no cracking or corrosion is found, apply a corrosion-
inhibiting compound to the accessible areas of the upper and lower 
chords of both the front and rear spars per Part I or Part II of the 
Accomplishment Instructions of Boeing Service Bulletin 737-57-1067, 
Revision 4, dated November 7, 1991, as applicable.
    (2) If any corrosion is found, repair per Part III of the 
Accomplishment Instructions of Boeing Service Bulletin 737-57-1067, 
Revision 4, dated November 7, 1991.
    (3) If a horizontal crack is found in the upper chords of the 
front or rear spars, repair per paragraph (f) of this AD.
    (4) If any cracking is found other than that identified in 
paragraph (d)(3) of this AD, repair per paragraph (d)(4)(i) or 
(d)(4)(ii) of this AD, as applicable.
    (i) If damage of the chords of the front or rear spar is within 
the limits specified in the service bulletin, before further flight, 
repair per Part III of the Accomplishment Instructions of Boeing 
Service Bulletin 737-57-1067, Revision 4, dated November 7, 1991.
    (ii) If damage of the chords of the front or rear spar exceeds 
the limits specified in the service bulletin, before further flight, 
repair per paragraph (f) of this AD.

Initial and Repetitive Eddy Current Inspections of Previous Repairs

    (e) For airplanes on which a previous repair to the upper chord 
of the front or rear spar was made per Boeing Service Bulletin 737-
57-1067, Revision 3, dated May 24, 1990, or earlier revisions: 
Within 12 months after the effective date of this AD, do an eddy 
current inspection of the repair area to detect cracking per a 
method approved by the Manager, Seattle Aircraft Certification 
Office (ACO), FAA. Repeat this inspection thereafter at intervals 
not to exceed 12

[[Page 21703]]

months. If any discrepancy is found, before further flight, repair 
per paragraph (f) of this AD. For a repair method to be approved by 
the Manager, SACO, as required by this paragraph, the approval 
letter must specifically reference this AD.

Repair

    (f) Repair (including removing corrosion; inspecting the rework 
area for cracks; refinishing the blend-out area; installing a 
nesting angle repair; and applying chemical film treatment, primer, 
sealant, and corrosion-inhibiting compound) any discrepancy 
specified in paragraphs (d)(3), (d)(4)(ii), and (e) of this AD, per 
a method approved by the Manager, Seattle ACO; or per data meeting 
the type certification basis of the airplane approved by a Boeing 
Designated Engineering Representative who has been authorized by the 
Manager, Seattle ACO, to make such findings. For a repair method to 
be approved by the Manager, Seattle ACO, as required by this 
paragraph, the approval letter must specifically reference this AD.

Alternative Methods of Compliance

    (g) 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, FAA. 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 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permit

    (h) Special flight permits may be issued per Secs. 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 April 24, 2001.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-10729 Filed 4-30-01; 8:45 am]
BILLING CODE 4910-13-U