[Federal Register Volume 63, Number 191 (Friday, October 2, 1998)]
[Proposed Rules]
[Pages 52992-52994]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-26354]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-189-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 supersedure of an existing 
airworthiness directive (AD), applicable to all Boeing Model 737-100, -
200, and -200C series airplanes, that currently requires periodic 
inspections to detect missing nuts and/or damaged secondary support 
hardware adjacent to the aft engine mount, and replacement, if 
necessary. That AD also provides for optional terminating action for 
certain inspections and a torque check. This action would mandate 
accomplishment of the previously optional terminating action. This 
proposal is prompted by the FAA's determination that the repetitive 
inspections required by the existing AD may not be providing the degree 
of safety assurance necessary for the transport airplane fleet. The 
actions specified by the proposed AD are intended to prevent failure of 
the secondary support to sustain engine loads in the event of failure 
of the aft engine mount cone bolt, which could result in the separation 
of the engine from the wing.

DATES: Comments must be received by November 16, 1998.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-189-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: Greg Schneider, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2028; 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

[[Page 52993]]

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-189-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-189-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On April 4, 1994, the FAA issued AD 91-09-14 R1, amendment 39-8876 
(59 FR 18294, April 18, 1994), applicable to all Boeing Model 737-100, 
-200, and -200C series airplanes, to require periodic inspections to 
detect missing nuts and/or damaged secondary support hardware adjacent 
to the aft engine mount, and replacement, if necessary. That AD also 
provides for optional installation of a new, modified support, which 
would constitute terminating action for certain inspections and a 
torque check. That action was prompted by the development of a 
modification that will prevent wearing of the secondary support. The 
requirements of that AD are intended to prevent failure of the 
secondary support to sustain engine loads in the event of failure of 
the aft engine mount cone bolt, which could result in the separation of 
the engine from the wing.

Actions Since Issuance of Previous Rule

    Since the issuance of AD 91-09-14 R1, Boeing has informed the FAA 
that, based on testing conducted by Boeing, significant cracks of the 
aft engine mount cone bolts may not be detected using the current 
ultrasonic inspection procedures. There have been two occurrences of 
failure of aft engine mount cone bolts after the bolts had been 
subjected to ultrasonic inspections. In light of this information, the 
FAA has determined that the repetitive inspections required by the 
existing AD may not be providing the degree of safety assurance 
necessary for the fleet of Boeing Model 737-100, -200, and -200C series 
airplanes.

Explanation of Relevant Service Information

    The FAA previously reviewed and approved Boeing Service Bulletin 
737-71-1289, dated August 19, 1993. That service bulletin describes 
procedures for replacement of the existing secondary support with a 
new, improved secondary support. Since the issuance of AD 91-09-14 R1, 
the FAA has reviewed and approved Boeing Notices of Status Change (NSC) 
737-71-1289 NSC 1, dated September 2, 1993; 737-71-1289 NSC 2, dated 
January 26, 1995; and 737-71-1289 NSC 03, dated October 3, 1996. These 
NSC's contain certain minor editorial changes to the service bulletin.

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 91-09-14 R1, to continue to require 
periodic inspections to detect missing nuts and/or damaged secondary 
support hardware, and replacement, if necessary. The proposed AD would 
require accomplishment of the previously optional terminating action, 
which, when accomplished, would constitute terminating action for 
certain inspections and for a torque check required by this AD.

Cost Impact

    There are approximately 1,045 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 382 airplanes of U.S. 
registry would be affected by this proposed AD.
    The inspections that are currently required by AD 91-09-14 R1 take 
approximately 3 work hours per airplane to accomplish, at an average 
labor rate of $60 per work hour. Based on these figures, the cost 
impact of the currently required actions on U.S. operators is estimated 
to be $68,760, or $180 per airplane, per inspection cycle.
    The replacement that is proposed in this AD would take 
approximately 60 work hours per airplane to accomplish, at an average 
labor rate of $60 per work hour. Required parts would cost 
approximately $7,000 per airplane. Based on these figures, the cost 
impact of the replacement proposed by this AD on U.S. operators is 
estimated to be $4,049,200, or $10,600 per airplane.
    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.

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 39-8876 (59 FR 
18294, April 18, 1994), and by adding a new airworthiness directive 
(AD), to read as follows:

Boeing: Docket 98-NM-189-AD. Supersedes AD 91-09-14 R1, amendment 
39-8876.

    Applicability: All Model 737-100, -200, and -200C series 
airplanes; 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)(1) 
of this AD. The request should include an assessment of

[[Page 52994]]

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 failure of the secondary support to sustain engine 
loads in the event of failure of the aft engine mount cone bolt, 
which could result in the separation of the engine from the wing, 
accomplish the following:
    (a) Within the next 45 landings after May 20, 1991 (the 
effective date of AD 91-09-14, amendment 39-6972), accomplish the 
following:
    (1) Inspect the aft mount cone bolt indicator for proper 
alignment. Improper alignment indicates a broken aft cone bolt. 
Broken cone bolts must be replaced, prior to further flight, with 
bolts that have been inspected in accordance with Boeing Alert 
Service Bulletin 737-71A1212, dated December 22, 1987, using 
magnetic particle inspection techniques. Repeat the inspection of 
the indicator at intervals thereafter not to exceed 45 landings.
    (2) Unless previously accomplished within the last 255 landings, 
inspect the aft mount cone bolt improved secondary support for 
missing nuts, evidence of bolt wear, and disbonded honeycomb core; 
in accordance with Boeing Service Bulletin 737-71-1250, dated June 
14, 1990. Except as provided in paragraph (b) of this AD, missing 
nuts, bolts worn outside the limits specified in the service 
bulletin, or disbonded honeycomb core must be replaced, prior to 
further flight, with new or repaired identical parts. Repeat the 
inspection at intervals not to exceed 300 landings.
    (b) Perform the following inspections if discrepant hardware is 
found during the inspections required by paragraph (a)(2) of this 
AD, and replacement hardware is not immediately available:
    (1) Prior to further flight, and thereafter at intervals not to 
exceed 300 landings, inspect for cracks in the aft engine mount cone 
bolt, in accordance with Boeing Alert Service Bulletin 737-71A1212, 
dated December 22, 1987, using ultrasonic inspection techniques. 
Replace cracked cone bolts, prior to further flight, with bolts that 
have been inspected in accordance with the service bulletin, using 
magnetic particle inspection techniques. Replacement (newly 
installed) cone bolts must be ultrasonically inspected for internal 
cracking in accordance with the provisions of this paragraph at 
intervals not to exceed 300 landings.
    (2) At the next ultrasonic inspection, as required by paragraph 
(b)(1) of this AD, unless previously accomplished within 150 to 300 
landings after cone bolt installation, accomplish a torque check to 
verify that the cone bolt is torqued to the proper torque limit 
specified in the appropriate Boeing maintenance manual. This check 
is to be accomplished without loosening the bolt. After each cone 
bolt installation, accomplish the torque check procedure required by 
this paragraph between 150 landings and 300 landings following 
installation. Replacement of discrepant hardware in accordance with 
paragraph (a)(2) of this AD constitutes terminating action for the 
requirements of this paragraph.
    (i) If the cone bolt torque is below one-half the specified 
torque, prior to further flight, remove the cone bolt and replace it 
with a serviceable bolt.
    (ii) If the cone bolt torque is equal to, or above one-half the 
specified torque, but below the specified torque, re-torque to the 
specified level and re-check the torque within the next 150 to 300 
landings. If, at that time, the torque is below 90 percent of the 
specified torque, replace the cone bolt with a serviceable bolt.
    (c) At next engine removal, or within 8,000 flight hours after 
the effective date of this AD, whichever occurs first, replace the 
secondary support of the aft engine mount with a new, improved 
secondary support, Kit Number 65C37057-1; in accordance with Boeing 
Service Bulletin 737-71-1289, dated August 19, 1993; as revised by 
Notices of Status Change 737-71-1289 NSC 1, dated September 2, 1993, 
737-71-1289 NSC 2, dated January 26, 1995, and 737-71-1289 NSC 03, 
dated October 3, 1996. Accomplishment of such replacement 
constitutes terminating action for the repetitive inspection 
requirements of paragraphs (a)(2) and (b)(1) of this AD, and for the 
torque check requirement of paragraph (b)(2) of this AD.
    (d)(1) 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.
    (d)(2) Alternative methods of compliance, approved previously in 
accordance with AD 91-09-14 R1, amendment 39-8876, are approved as 
alternative methods of compliance with paragraph (a)(1) of this AD.

    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 September 25, 1998.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-26354 Filed 10-1-98; 8:45 am]
BILLING CODE 4910-13-U