[Federal Register Volume 59, Number 74 (Monday, April 18, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-8418]


[[Page Unknown]]

[Federal Register: April 18, 1994]



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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 93-NM-170-AD; Amendment 39-8876; AD 91-09-14 R1]

 

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

AGENCY: Federal Aviation Administration, DOT.


ACTION: Final rule.

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SUMMARY: This amendment revises 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 
engine aft mount, and replacement, if necessary. This amendment 
provides for the optional installation of a new, modified support, 
which, if accomplished, constitutes terminating action for certain 
required inspections. This amendment is prompted by the development of 
a modification that will prevent wearing of the secondary support. The 
actions specified by this 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: Effective May 18, 1994.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of May 18, 1994.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the Federal 
Aviation Administration (FAA), Transport Airplane Directorate, Rules 
Docket, 1601 Lind Avenue SW., Renton, Washington; or at the Office of 
the Federal Register, 800 North Capitol Street NW., suite 700, 
Washington, DC.

FOR FURTHER INFORMATION CONTACT: Thomas Rodriguez, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office (ACO), 1601 Lind Avenue SW., Renton, 
Washington 98055-4056; telephone (206) 227-2779; fax (206) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations by revising AD 91-09-14, Amendment 39-6972 (56 FR 
18696, April 24, 1991), which is applicable to all Boeing Model 737-
100, -200, and -200C series airplanes, was published in the Federal 
Register on December 29, 1993 (58 FR 68787). Among other things, AD 91-
09-14 currently requires periodic inspections to detect missing nuts 
and/or damaged secondary support hardware, and replacement, if 
necessary. The notice proposed to revise AD 91-09-14 to provide for the 
optional replacement of the existing aft engine mount secondary support 
with a new, modified secondary support. If accomplished, such 
replacement would constitute terminating action for certain of the 
currently required inspections.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.
    All of the commenters support the proposal.
    One commenter, Boeing, notes that the number of work hours 
necessary to accomplish the optional modification is closer to 60 work 
hours rather than 30 work hours, as was indicated in the cost impact 
information presented in the preamble to the notice. The FAA 
acknowledges this updated figure and has revised the cost impact 
information, below, to reflect it.
    After careful review of the available data, including the comments 
noted above, the FAA has determined that air safety and the public 
interest require the adoption of the rule as proposed.
    There are approximately 1,144 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 432 
airplanes of U.S. registry will be affected by this AD.
    The actions currently required by AD 91-09-14 take approximately 3 
work hours per airplane to accomplish, at an average labor rate of $55 
per work hour. Based on these figures, the total cost impact of the 
currently required actions on U.S. operators is estimated to be 
$71,280, or $165 per airplane, per inspection cycle.
    This revision of AD 91-09-14 adds no new additional costs to 
operators, since it merely provides for an optional installation that 
would provide terminating action for certain requirements. Should an 
operator elect to accomplish the installation, the associated actions 
will take approximately 60 work hours per airplane to accomplish, at an 
average labor rate of $55 per work hour. Required parts will cost 
approximately $6,818 per airplane. Based on these figures, the total 
cost of accomplishing the optional installation is estimated to be 
$10,118 per airplane.
    The regulations adopted herein will 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 final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under DOT Regulatory Policies and 
Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action 
and it is contained in the Rules Docket. A copy of it may be obtained 
from the Rules Docket at the location provided under the caption 
ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety. Adoption of the Amendment.

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

PART 39--AIRWORTHINESS DIRECTIVES

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

    Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 
106(g); and 14 CFR 11.89.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by removing amendment 39-6972 (56 FR 
18696, April 24, 1991), and by adding a new airworthiness directive 
(AD), amendment 39-8876, to read as follows:

91-09-14 R1 Boeing: Amendment 39-8876. Docket 93-NM-170-AD. Revises 
AD 91-09-14, Amendment 39-6972.

    Applicability: All Model 737-100, -200, and -200C series 
airplanes, certificated in any category.
    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 engine separation 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 above 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 every 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, 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) Replacement of the existing aft engine mount secondary 
support with a new, modified secondary support, Kit Number 65C37057-
1, in accordance with Boeing Service Bulletin 737-71-1289, dated 
August 19, 1993, constitutes terminating action for the inspections 
required by paragraphs (a)(2), (b), (b)(1), and (b)(2) 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.

    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 
Federal Aviation Regulations (FAR) 21.197 and 21.199 to operate the 
airplane to a location where the requirements of this AD can be 
accomplished.
    (f) The optional replacement shall be done in accordance with 
Boeing Service Bulletin 737-71-1289, dated August 19, 1993. This 
incorporation by reference was approved by the Director of the 
Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 
51. Copies may be obtained from Boeing Commercial Airplane Group, 
P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be 
inspected at the FAA, Transport Airplane Directorate, 1601 Lind 
Avenue SW., Renton, Washington; or at the Office of the Federal 
Register, 800 North Capitol Street NW., suite 700, Washington, DC.
    (g) This amendment becomes effective on May 18, 1994.

    Issued in Renton, Washington, on April 4, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-8418 Filed 4-15-94; 8:45 am]
BILLING CODE 4910-13-U