[Federal Register Volume 64, Number 79 (Monday, April 26, 1999)]
[Proposed Rules]
[Pages 20224-20226]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-10347]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-21-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, and -200C 
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 737-100, -
200, and -200C series airplanes. This proposal would require 
inspections to detect corrosion and cracking of the inboard track of 
each outboard flap where the track attaches to the rear spar, and 
repair, if necessary. For certain airplanes, this proposal also 
provides for optional terminating action for the repetitive inspections 
required for those airplanes. This proposal is prompted by several 
reports of cracking of the inboard track of the outboard flap. The 
actions specified by the proposed AD are intended to detect and correct 
corrosion and cracking of the inboard track of the outboard flap, which 
could result in loss of the outboard trailing edge flap and consequent 
reduced controllability of the airplane.

DATES: Comments must be received by June 10, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-21-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: Rick Kawaguchi, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-1153; 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 99-NM-21-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-21-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports indicating that cracking of the 
inboard track of the outboard flap where the track attaches to the rear 
spar has been found on several airplanes. Such cracking has been 
attributed to stress corrosion. Corrosion in that area can be 
accelerated if a phenolic rub strip is installed at the interface 
between the flap track and wing skin. (The rub strip is intended to 
protect the surface of the wing skin from abrasion.) The phenolic rub 
strip may draw moisture into the interface, which could result in 
corrosion. Also, inadequate clamp-up of the attachment bolts can make 
the area where the flap track attaches to the rear spar more vulnerable 
to moisture absorption and, consequently, to corrosion. Such corrosion, 
if not corrected, could result in cracking of the inboard flap track, 
which could result in loss of the outboard trailing edge flap and 
consequent reduced controllability of the airplane.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 737-57-
1065, Revision 3, dated December 17, 1982. That service bulletin 
describes, among other things, procedures for a preventive modification 
of the interface between the inboard track of the outboard flap and the 
rear spar. The modification involves replacing the existing rub strip 
with an aluminum rub strip; replacing the existing shim, if necessary; 
and replacing certain attachment bolts with new attachment bolts. 
Accomplishment of the modification specified in the 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, for certain airplanes, repetitive visual 
inspections to detect corrosion, and repetitive high frequency eddy 
current (HFEC) inspections to detect cracking, of the inboard track of 
each outboard flap where the track attaches to the rear spar, and 
repair, if necessary. For certain other airplanes, the proposed AD 
would require a one-time visual inspection to detect corrosion, and a 
one-time HFEC inspection to detect cracking, of the inboard track of 
each outboard flap where the track attaches to the rear spar, and 
repair, if necessary. The HFEC inspections would be required to be 
accomplished in accordance with the Boeing 737 Nondestructive Test 
Manual.
    For certain airplanes, the proposed AD also provides an optional 
terminating action for the repetitive inspection requirement. This 
action would be required to be accomplished in accordance with the 
service bulletin described previously, except as discussed below.

[[Page 20225]]

Differences Between the Service Bulletin and the Proposed AD

    Boeing Service Bulletin 737-57-1065, Revision 3, describes visual 
inspections of the outboard flap to detect looseness, gaps, and missing 
or damaged rub strips and shims. Operators should note that the 
proposed AD would not require these inspections. This decision is based 
on the fact that the intent of this proposed AD is to detect and 
correct corrosion and cracking of the inboard track of the outboard 
flap where the track attaches to the rear spar. The FAA finds that the 
visual inspections described in the service bulletin were not intended 
to detect corrosion or cracks, and therefore may not ensure that any 
corrosion or cracking is detected in a timely manner. Therefore, this 
proposed AD would require repetitive visual inspections to detect 
corrosion, and repetitive HFEC inspections to detect cracking, of the 
inboard track of each outboard flap in order to ensure that any 
corrosion cracking is detected in a timely manner.
    In addition, the service bulletin describes a one-time visual 
inspection to determine if the inboard attachment bolt holes are 
aligned properly. Operators should note that this proposed AD does not 
require that inspection because the FAA finds that it is not relevant 
to detection of cracks.
    Operators also should note that, although the actions described in 
the service bulletin are specified for both the inboard and outboard 
tracks of each outboard flap, this proposed AD is applicable only to 
the inboard track of each outboard flap. This decision is based upon 
the fact that the inboard track of the outboard flap is more heavily 
loaded than the outboard track, and corrosion cracking has been 
reported only on the inboard track.
    Operators also should note that the effectivity listing of the 
service bulletin specifies only Boeing Model 737 series airplanes 
having line numbers (L/N) 1 through 869 inclusive. This AD is 
applicable to Boeing Model 737-100, -200, and -200C series airplanes 
having L/N's 1 through 869 inclusive; as well as Boeing Model 737-100, 
-200, and -200C series airplanes having L/N's 870 through 1585 
inclusive, on which the #2 or #7 flap track has been replaced with a 
part having certain Boeing part numbers. The subject flap tracks may 
have been removed from an airplane having a L/N 1 through 869 and re-
installed, without being inspected, on another airplane having a L/N 
870 through 1585. Therefore, to ensure that cracking on the subject 
flap tracks is detected in a timely manner, the FAA finds it necessary 
to expand the applicability of this AD by mandating one-time 
inspections of airplanes with L/N's 870 through 1585 inclusive on which 
certain flap tracks have been installed.

Cost Impact

    There are approximately 1,020 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 394 airplanes of U.S. 
registry would be affected by this proposed AD.
    It would take approximately 16 work hours per airplane to 
accomplish the proposed inspections, 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 
$378,240, or $960 per airplane, per inspection cycle.
    The cost impact figure discussed above is 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.
    Should an operator elect to accomplish the optional terminating 
action that would be provided by this AD action, it would take 
approximately 96 work hours to accomplish it, at an average labor rate 
of $60 per work hour. The cost of required parts would be approximately 
$548 per airplane. Based on these figures, the cost impact of the 
optional terminating action would be $6,308 per airplane.

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 99-NM-21-AD.

    Applicability: Model 737-100, -200, and -200C series airplanes, 
line numbers (L/N) 1 through 869 inclusive; and Model 737-100, -200, 
and -200C series airplanes, L/N 870 through 1585 inclusive, on which 
the #2 or #7 flap track has been replaced with a part having a part 
number (P/N) listed in Table 1 of this AD; certificated in any 
category.

             Table 1.--Boeing Flap Tracks Subject to this AD
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                          Name                               Part No.
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Boeing..................................................      65-67158-2
                                                              65-67158-3
                                                              65-46428-2
                                                              65-46428-3
                                                              65-46428-5
                                                              65-46428-7
                                                              65-46428-9
                                                             65-46428-11
                                                             65-46428-15
                                                             65-46428-17
                                                             65-46428-19
                                                             65-46428-21
                                                             65-46428-23
                                                             65-46428-25
                                                             65-46428-27
                                                             65-46428-33
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    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 (f) 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

[[Page 20226]]

eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To detect and correct corrosion or cracking of the inboard track 
of each outboard flap where the track attaches to the rear spar, 
which could result in loss of the outboard trailing edge flap and 
consequent reduced controllability of the airplane, accomplish the 
following:

Inspections

    (a) Within 18 months after the effective date of this AD, 
accomplish the requirements of paragraphs (a)(1) and (a)(2) of this 
AD.
    (1) Perform a detailed visual inspection to detect corrosion on 
the surface and edges of the inboard track of each outboard flap 
where the track attaches to the rear spar.
    (2) Perform a high frequency eddy current (HFEC) inspection to 
detect cracking on the surface and edges of the inboard track of 
each outboard flap where the track attaches to the rear spar, in 
accordance with Subject 51-00-00, Figure 13, of the Boeing 737 
Nondestructive Test (NDT) Manual (Boeing Document D6-37239); and 
remove the attachment bolts and perform an open-hole HFEC inspection 
of the bolt holes for cracking, in accordance with Subject 51-00-00, 
Figure 2 or 19, of the Boeing 737 NDT Manual.
    (b) For airplanes having L/N 1 through 869 inclusive, on which 
no corrosion or cracking is detected during the inspections required 
by paragraph (a) of this AD: Prior to further flight, re-install the 
attachment bolts. Repeat both inspections thereafter at intervals 
not to exceed 18 months.
    (c) For airplanes having L/N 870 through 1585 inclusive, on 
which replacement flap tracks are installed, and on which no 
corrosion or cracking is detected during the inspections required by 
paragraph (a) of this AD: No further action is required by this AD.

Repair

    (d) If any corrosion or cracking is detected during any 
inspection required by paragraph (a) or (b) of this AD, prior to 
further flight, repair in accordance with a method approved by the 
Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport 
Airplane Directorate; or in accordance with data meeting the type 
certification basis of the airplane approved by a Boeing Company 
Designated Engineering Representative who has been authorized by the 
Manager, Seattle ACO, to make such findings. For a repair method to 
be approved, as required by this paragraph, the approval letter must 
specifically reference this AD.

Optional Terminating Action

    (e) Modification of the interface between the inboard track of 
each outboard flap and the rear spar in accordance with Boeing 
Service Bulletin 737-57-1065, Revision 3, dated December 17, 1982, 
constitutes terminating action for the repetitive inspection 
requirement of paragraph (b) of this AD.

Alternative Methods Of Compliance

    (f) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle ACO. Operators shall submit 
their requests through an appropriate FAA Principal Maintenance 
Inspector, who may add comments and then send it to the Manager, 
Seattle ACO.

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

Special Flight Permits

    (g) 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 April 20, 1999.
D. L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-10347 Filed 4-23-99; 8:45 am]
BILLING CODE 4910-13-P