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[Federal Register Volume 62, Number 4 (Tuesday, January 7, 1997)]
[Proposed Rules]
[Pages 945-947]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-254]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 95-NM-215-AD]

Airworthiness Directives; Boeing Model 737-100 and -200 Series 
Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing 
airworthiness directive (AD), applicable to certain Boeing Model 737-
100 and -200 series airplanes, that currently requires various 
inspections for cracks in the outboard chord of the frame at body 
station (BS) 727 and in the outboard chord of stringer 18A; and repair 
or replacement of cracked parts. That AD was prompted by reports of 
fatigue cracks in those outboard chords. This action would add 
inspections for certain airplanes, and would revise certain compliance 
times for all airplanes. The actions specified by the proposed AD are 
intended to detect and correct fatigue cracking, which could result in 
reduced structural integrity of the outboard chords, and subsequent 
rapid decompression of the airplane.

DATES: Comments must be received by February 18, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 95-NM-215-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: Della Swartz, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2785; 
fax (206) 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 95-NM-215-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-103, Attention: Rules 
Docket No. 95-NM-215-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On June 5, 1995, the FAA issued AD 95-12-17, amendment 39-9268 (60 
FR 36981, July 19, 1995), applicable to certain Boeing Model 737-100 
and -200 series airplanes, to require various inspections for cracks in 
the outboard chord of the frame at body station (BS) 727 and in the 
outboard chord of stringer 18A; and repair or replacement of cracked 
parts. That AD also provides for an optional terminating action for the 
required inspections. That action was prompted by reports of fatigue 
cracks in those outboard chords. The requirements of that AD are 
intended to detect and correct such fatigue cracking, which could 
result in reduced structural integrity of the outboard chords, and 
subsequent rapid decompression of the airplane.

[[Page 946]]

Actions Since Issuance of Previous Rule

    Since the issuance of that AD, the FAA has become aware that 
certain airplanes that should be subject to the requirements of that AD 
were omitted inadvertently. At the time AD 95-12-17 was issued, the 
Boeing service bulletins cited in the AD did not describe initial or 
repetitive inspections for unmodified airplanes that had accumulated 
less than 27,000 total flight cycles. The FAA has determined that 
airplanes that have accumulated less than 27,000 total flight cycles as 
of August 18, 1995, (the effective date of AD 95-12-17) are subject to 
the addressed unsafe condition. The FAA finds that these airplanes also 
must be inspected to detect cracking in the outboard chords in order to 
address the identified unsafe condition in a timely manner.
    Additionally, several operators have expressed their concern with 
the complexity of the compliance times of AD 95-12-17. The operators 
have advised the FAA that the currently required ``progressive'' or 
``sliding'' compliance times are difficult to track and to schedule. 
These operators maintain that the complexity of the compliance times, 
in itself, will increase the risk and likelihood of a missed inspection 
occurring because of an inadvertent scheduling oversight.
    The FAA acknowledges the commenters' concern. Since the issuance of 
AD 95-12-17, the FAA has held further discussions with the manufacturer 
in an effort to clarify and simplify the compliance times. For 
airplanes on which the upper outboard chord has been replaced, the 
compliance times of this proposal reflect a revised initial threshold 
of ``prior to the accumulation of 50,000 flight cycles since 
replacement of the upper outboard chord, or within 4,500 flight cycles 
as of the effective date of this AD, whichever occurs later.'' For all 
other airplanes, the compliance times of this proposal reflect a 
revised initial threshold of ``prior to the accumulation of 50,000 
total flight cycles, or within 4,500 flight cycles after the effective 
date of this AD, whichever occurs later.'' The repetitive inspections 
would be required at intervals not to exceed 4,500 flight cycles for 
all affected airplanes. The FAA has determined that the revised 
compliance times will address the unsafe condition in a timely manner.

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 supersede AD 95-12-17 to continue to require various 
inspections to detect cracking in the outboard chord of the frame at BS 
727 and in the outboard chord of stringer 18A; and repair or 
replacement of cracked parts. This action would add inspections for 
certain airplanes. This action also would revise the threshold for 
accomplishment of the initial inspection and would revise the 
repetitive inspection interval for all affected airplanes. This action 
also continues to provide for an optional terminating action for the 
required inspections. The actions would be required to be accomplished 
in accordance with Boeing Alert Service Bulletin 737-53A1166, which is 
cited in AD 95-12-17 as the appropriate source of service information.

Cost Impact

    There are approximately 999 Model 737-100 and -200 series airplanes 
of the affected design in the worldwide fleet. The FAA estimates that 
296 airplanes of U.S. registry would be affected by this proposed AD.
    The actions that are currently required by AD 95-12-17 take 
approximately 4 work hours per airplane to accomplish, at an average 
labor rate of $60 per work hour. Based on these figures, the cost 
impact on U.S. operators of the actions currently required is estimated 
to be $71,040, or $240 per airplane, per inspection cycle.
    This proposed AD specifies inspection requirements for airplanes 
that were omitted inadvertently from the existing AD. However, the 
costs associated with the inspections for those airplanes were included 
previously in the cost impact on U.S. operators for accomplishment of 
AD 95-12-17. Therefore, the FAA estimates that no additional costs 
would be required for accomplishment of the proposed requirements of 
this AD.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the current or 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 will be provided by this AD action, it will take 
approximately 50 work hours to accomplish it, at an average labor rate 
of $60 per work hour. Required parts will cost approximately $3,680 per 
airplane. Based on these figures, the cost impact of this optional 
terminating action is estimated to be $6,680 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 removing amendment 39-9268 (60 FR 
36981, July 19, 1995), and by adding a new airworthiness directive 
(AD), to read as follows:

Boeing: Docket 95-NM-215-AD. Supersedes AD 95-12-17, Amendment 39-
9268.

    Applicability: Model 737-100 and -200 series airplanes; line 
numbers 1 through 999 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 
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

[[Page 947]]

of the requirements of this AD is affected, the owner/operator must 
use the authority provided in paragraph (f) of this AD to request 
approval from the FAA. This approval may address either no action, 
if the current configuration eliminates the unsafe condition; or 
different actions necessary to address the unsafe condition 
described in this AD. Such a request should include an assessment of 
the effect of the changed configuration on the unsafe condition 
addressed by this AD. In no case does the presence of any 
modification, alteration, or repair remove any airplane from the 
applicability of this AD.

    Compliance: Required as indicated, unless accomplished 
previously.
    To detect and correct fatigue cracking, which could result in 
reduced structural integrity of the outboard chords, and subsequent 
rapid decompression of the airplane, accomplish the following:
    (a) For airplanes on which the body station (BS) 727 frame upper 
outboard chord has been replaced in accordance with Boeing Service 
Bulletin 737-53-1088: Prior to the accumulation of 50,000 flight 
cycles since replacement of the upper outboard chord, or within 
4,500 flight cycles after the effective date of this AD, whichever 
occurs later, perform close visual, pulse echo shear wave (PESW), 
and high frequency eddy current (HFEC) inspections to detect cracks 
in the outboard chord of the frame at BS 727 and in the outboard 
chord of stringer 18A. Perform the inspections in accordance with 
Part I of the Accomplishment Instructions of either Boeing Alert 
Service Bulletin 737-53A1166, dated June 30, 1994; or Boeing Service 
Bulletin 737-53A1166, Revision 1, dated May 25, 1995. Thereafter, 
repeat these inspections at intervals not to exceed 4,500 flight 
cycles.
    (b) For airplanes on which the BS 727 frame outboard chord has 
not been replaced or on which only the lower outboard chord has been 
replaced in accordance with Boeing Service Bulletin 737-53-1088: 
Prior to the accumulation of 50,000 total flight cycles, or within 
4,500 flight cycles after the effective date of this AD, whichever 
occurs later, perform close visual, PESW, and HFEC inspections to 
detect cracks in the outboard chord of the frame at BS 727 and in 
the outboard chord of stringer 18A. Perform the inspections in 
accordance with Part I of the Accomplishment Instructions of either 
Boeing Alert Service Bulletin 737-53A1166, dated June 30, 1994; or 
Boeing Service Bulletin 737-53A1166, Revision 1, dated May 25, 1995. 
Thereafter, repeat these inspections at intervals not to exceed 
4,500 flight cycles.
    (c) If any crack is found in the outboard chord of stringer 18A 
during any inspection required by this AD, prior to further flight, 
repair in accordance with either paragraph (c)(1) or (c)(2) of this 
AD.
    (1) Repair in accordance with Boeing Service Bulletin 737-
53A1166, Revision 1, dated May 25, 1995; or
    (2) Repair in accordance with a method approved by the Manager, 
Seattle Aircraft Certification Office, (ACO) FAA, Transport Airplane 
Directorate.
    (d) If any crack is found in the outboard chord of the frame at 
BS 727 during any inspection required by this AD: Accomplish 
paragraph (d)(1) or (d)(2) of this AD, as applicable, in accordance 
with either Boeing Alert Service Bulletin 737-53A1166, dated June 
30, 1994; or Boeing Service Bulletin 737-53A1166, Revision 1, dated 
May 25, 1995. Thereafter, repeat the inspections required by either 
paragraph (a) or (b) of this AD, as applicable, at intervals not to 
exceed 4,500 flight cycles.
    (1) If any crack extends from the forward edge of the chord or 
from the forward fastener hole, but does not extend past the second 
fastener hole, accomplish either paragraph (d)(1)(i) or (d)(1)(ii) 
of this AD.
    (i) Prior to further flight, install the time-limited repair. 
Prior to the accumulation of 4,500 flight cycles or within 18 months 
after accomplishment of the repair, whichever occurs first, replace 
the outboard chord. Or
    (ii) Prior to further flight, replace the outboard chord.

    Note 2: Boeing Alert Service Bulletin 737-53A1166 references 
Boeing Service Bulletin 737-53-1088 as an additional source of 
service information for procedures to replace the chord.

    (2) If any crack extends from the forward edge of the chord, or 
from the forward fastener hole, and extends past the second fastener 
hole, prior to further flight, replace the outboard chord in 
accordance with either the original issue or Revision 1 of the 
service bulletin.
    (e) Accomplishment of the following actions in accordance with 
either Boeing Alert Service Bulletin 737-53A1166, dated June 30, 
1994, or Boeing Service Bulletin 737-53A1166, Revision 1, dated May 
25, 1995, constitutes terminating action for the requirements of 
this AD.
    (1) For airplanes on which no crack is found: Install the 
preventative modification in accordance with either the original 
issue or Revision 1 of the service bulletin.
    (2) For airplanes on which any crack is found: Prior to further 
flight, replace the cracked chord and install the preventative 
modification in accordance with either the original issue or 
Revision 1 of the service bulletin.
    (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 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (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 December 31, 1996.
S. R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-254 Filed 1-6-97; 8:45 am]
BILLING CODE 4910-13-U
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