[Federal Register Volume 64, Number 243 (Monday, December 20, 1999)]
[Rules and Regulations]
[Pages 70997-71000]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-32509]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-189-AD; Amendment 39-11466; AD 99-26-07]
RIN 2120-AA64


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 supersedes 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 amendment requires accomplishment of the previously 
optional terminating action. This amendment 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 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 January 24, 2000.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of January 24, 2000.
    The incorporation by reference of Boeing Service Bulletin 737-71-
1289, dated August 19, 1993, as listed in the regulations, was approved 
previously by the Director of the Federal Register as of May 18, 1994 
(59 FR 18294, April 18, 1994).

ADDRESSES: The service information referenced in this AD may be 
obtained

[[Page 70998]]

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: 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: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) by superseding AD 91-09-14 R1, 
amendment 39-8876 (59 FR 18294, April 18, 1994), which is applicable to 
all Boeing Model 737-100, -200, and -200C series airplanes, was 
published in the Federal Register on October 2, 1998 (63 FR 52992). The 
action proposed to continue to require periodic inspections to detect 
missing nuts and/or damaged secondary support hardware adjacent to the 
aft engine mount, and replacement, if necessary. The action also 
proposed to mandate accomplishment of the previously optional 
terminating action.

Comments

    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

Support for the Proposed Rule

    Two commenters support the proposed rule.

Requests to Revise Compliance Time of Paragraph (c) of the Proposed 
AD

    Two commenters request that the compliance time in paragraph (c) of 
the proposed AD be revised by removing the threshold ``at next engine 
removal'' and setting the threshold simply to ``within 8,000 flight 
hours after the effective date of this AD.'' One commenter states that 
the requirement to accomplish the terminating action (i.e., 
installation of Boeing Secondary Support, Kit Number 65C37057-1) is 
overly restrictive. Operators would have to be prepared to modify the 
secondary support (i.e., install the secondary support kit) at any 
unscheduled engine change, even though the conditions that lead to an 
unscheduled engine removal are not likely to affect safety of the 
secondary support. Another commenter states that the threshold of ``at 
next engine removal'' in paragraph (c) of the proposed rule is too 
harsh. The commenter states that it accomplishes a magnetic particle 
inspection of the aft engine mount cone bolt during each engine 
removal, and that these inspections are more than adequate to ensure 
the integrity of the aft mount cone bolt until the modification is 
accomplished at 8,000 flight hours.
    The FAA partially concurs with the commenters' request to revise 
the compliance time specified in paragraph (c) of the AD. The FAA's 
intent was to require installation at the next ``scheduled'' engine 
removal, or within 8,000 flight hours after the the effective date of 
this AD, whichever occurs first, which is the typical interval between 
scheduled engine changes/overhauls. The FAA agrees that the threshold 
should not be subject to ``unscheduled'' engine removals, but does not 
agree that the threshold should be set solely to ``within 8,000 flight 
hours,'' as suggested by the commenters. The FAA has determined that a 
compliance time at the next ``scheduled'' engine removal, or within 
8,000 flight hours after the effective date of the AD, whichever occurs 
first, will provide operators adequate time to procure and install the 
secondary support kit, and will not be an unnecessary burden on 
operators.
    In addition, the FAA does not agree with the second commenter that 
a magnetic particle inspection of the cone bolt during the engine 
removal will ensure that cracks will not initiate prior to the next 
engine removal. The magnetic inspection only ensures that the bolts 
being installed have no detectable cracks. In light of the results of 
testing conducted by Boeing and the two occurrences of failure of the 
aft engine mount cone bolts after the bolts had been subjected to 
ultrasonic inspections, the FAA finds that installation of a new, 
improved secondary support at the next scheduled engine removal, or 
within 8,000 flight hours after the effective date of this AD, 
whichever occurs first, is necessary to address the identified unsafe 
condition.
    Therefore, the FAA has revised the compliance time of paragraph (c) 
of the final rule accordingly.
    One commenter requests that the compliance time in paragraph (c) of 
the proposed AD coincide with its hush kit installation schedule. The 
commenter states that its hush kit schedule will occur prior to the 
proposed 8,000-flight hour threshold, but may not occur prior to the 
next engine removal. The commenter also states that aligning the 
compliance time with the hush kit installation will avoid the dual cost 
of installing the Boeing secondary support kit at the next engine 
removal at a cost of $10,600 per aircraft, and replacing it within one 
year as part of the NORDAM hush kit installation.
    The FAA partially concurs with the commenter's request to revise 
the subject compliance time. The FAA finds that a threshold of ``at the 
next engine removal'' may result in the unnecessary installation and 
removal of the Boeing secondary support kit for those operators 
currently working to a schedule for incorporation of the NORDAM hush 
kit. However, the FAA finds that a compliance time of at the next 
``scheduled'' engine removal, or within 8,000 flight hours after the 
effective date of the AD, whichever occurs first, will preclude any 
unnecessary installation and removal of the Boeing secondary support 
kit. The FAA based its determination on an expectation that operators 
will not schedule an engine change/overhaul within 12 months prior to 
installing a hush kit, but rather will schedule both to coincide in 
order to minimize down time. As discussed previously, the FAA has 
revised the threshold of paragraph (c) to at the next ``scheduled'' 
engine removal.

Requests to Allow an Alternative Method of Compliance (AMOC)

    Two commenters request that paragraph (c) of the proposed AD be 
revised to include a statement that installation of certain NORDAM hush 
kits is an AMOC to the requirement to install the Boeing secondary 
support, Kit Number 65C37057-1. The commenters state that they are 
currently installing a certain NORDAM hush kit, and that this hush kit 
has been approved by the Seattle Aircraft Certification Office (SACO), 
FAA, Transport Airplane Directorate, as an AMOC to AD 91-09-14 R1. 
Specifically, the installation of NORDAM Low Gross Weight (LGW) Hush 
Kit [i.e., Supplementary Type Certificate (STC) ST00131SE] has been 
approved by the FAA as terminating action for the inspections mandated 
by AD 91-09-14 R1, with the exception of the repetitive inspections of 
the aft cone bolt failure indicator required in paragraph (a)(1) of AD 
91-09-14 R1. The commenters state that this approval indicates that the 
secondary support that is installed as part of the NORDAM hush kit 
should provide an acceptable level of safety and meet the intent of the 
proposed rule.
    The FAA concurs with the commenters' request to include a statement 
in paragraph (c) of the final rule to clarify this point. The FAA has 
revised the final rule to include a new

[[Page 70999]]

NOTE to specify that installation of certain NORDAM hush kits is 
considered an acceptable AMOC to the requirements of this AD, and is 
considered terminating action for the inspections mandated by this AD, 
except for the repetitive inspections of the aft cone bolt failure 
indicator required in paragraph (a)(1) of this AD. The repetitive 
inspections of the aft cone bolt failure indicator specified in 
paragraph (a)(1) are still required. In addition, the FAA finds that 
paragraph (d)(2) of the final rule also must be revised to clarify this 
point.

Requests to Not Mandate Replacement of Secondary Support

    One commenter requests that the FAA continue to require the current 
inspections required by AD 91-09-14 R1 and continue to provide the 
optional terminating action (i.e., replacement of the secondary support 
of the aft engine mount with a new, improved secondary support) rather 
than mandating it. Another commenter questions the necessity of the 
proposed rule based upon existing mandates that will provide an 
equivalent means of compliance with a similar time period. One 
commenter states that it has been inspecting the aft mount cone bolt 
indicator for alignment during every over-night check in accordance 
with its maintenance policy and has been inspecting the secondary 
support hardware (i.e., the aft mount cone bolt and nut) in accordance 
with AD 91-09-14 R1. The commenter also states that it has been 
replacing the forward and aft mount cone bolt, nut, and vibration 
isolator every 6,000 flight hours or engine hard time, or at any engine 
removal, whichever occurs first. The commenter notes that it has not 
detected a failure of the secondary support hardware in the aft mount 
cone bolt, or detected loosening of the nut.
    The FAA does not concur with the commenter's request to not mandate 
accomplishment of the previously optional terminating action. As 
discussed in the preamble of the proposed rule, 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 transport 
airplane fleet. The 45-day inspection interval of the aft cone bolt 
failure indicator, as specified in the existing AD, may not detect a 
broken aft cone bolt in a timely manner, as cracks in the aft cone bolt 
may go undetected using the current ultrasonic inspection procedures. 
Worn secondary support components that exceed the wear limits allowed 
in the AD 91-09-14 R1 may not be reliably detected due to human factors 
and may, in the event of the failure of an aft cone bolt, render the 
secondary support incapable of supporting the aft end of the engine 
until the next inspection of the aft cone bolt failure indicator. 
Therefore, the FAA has determined that the repetitive inspections may 
not be adequate to preclude an engine separation, and finds that 
installation of the new Boeing secondary support kit should be 
mandated.

Conclusion

    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 with the changes previously 
described. The FAA has determined that these changes will neither 
increase the economic burden on any operator nor increase the scope of 
the AD.

Cost Impact

    There are approximately 1,045 Model 737-100, -200, and -200C series 
airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 382 airplanes of U.S. registry will be affected by this 
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 inspections on U.S. operators is 
estimated to be $68,760, or $180 per airplane, per inspection cycle.
    The replacement that is required by this AD will take approximately 
60 work hours per airplane to accomplish, at an average labor rate of 
$60 per work hour. Required parts will cost approximately $7,000 per 
airplane. Based on these figures, the cost impact of the new 
requirements of 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 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 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 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), amendment 39-11466, to read as follows:

99-26-07  Boeing: Amendment 39-11466. Docket 98-NM-189-AD. 
Supersedes AD 91-09-14 R1, Amendment 39-8876.

    Applicability: All Model 737-100, -200, and -200C 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 (e)(1) 
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.


[[Page 71000]]


    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:

Restatement of Requirements of AD 91-09-14, Amendment 39-6972

Repetitive Inspections and Replacement, If Necessary

    (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.

Follow-On Inspections, Replacement, and Torque Check

    (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.

New Actions Required by This AD

Replacement

    (c) At the next scheduled 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.

Optional Installation

    (d) Installation of Nordam hush kits modified in accordance with 
the following Supplemental Type Certificate is considered acceptable 
for compliance with the requirements of paragraphs (a)(2), (b), and 
(c) of this AD, but are not considered acceptable for compliance 
with the requirements of paragraph (a)(1) of this AD.
     SA5730NM, issued on June 26, 1992 and amended on 
October 2, 1992; or
     ST00131SE, issued on November 8, 1994, and amended on 
January 26, 1995, May 13, 1996, September 13, 1996, and February 20, 
1997.

Alternative Methods of Compliance

    (e)(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.

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

    (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 the requirements of this AD, 
except for the requirements of paragraph (a)(1) of this AD.

Special Flight Permits

    (f) 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.

Incorporation by Reference

    (g) The inspection required by paragraph (a)(2) of this AD shall 
be done in accordance with Boeing Service Bulletin 737-71-1250, 
dated June 14, 1990. The inspection required by paragraph (b)(1) of 
this AD shall be done in accordance with Boeing Alert Service 
Bulletin 737-71A1212, dated December 22, 1987. The replacement 
required by paragraph (c) of this AD shall be done in accordance 
with Boeing Service Bulletin 737-71-1289, dated August 19, 1993, as 
revised by Notice of Status Change 737-71-1289 NSC 1, dated 
September 2, 1993, Notice of Status Change 737-71-1289 NSC 2, dated 
January 26, 1995, and Notice of Status Change 737-71-1289 NSC 03, 
dated October 3, 1996.
    (1) The incorporation by reference of Boeing Service Bulletin 
737-71-1250, dated June 14, 1990; Boeing Alert Service Bulletin 737-
71A1212, dated December 22, 1987, Boeing Service Bulletin Notice of 
Status Change 737-71-1289 NSC 1, dated September 2, 1993, Boeing 
Service Bulletin Notice of Status Change 737-71-1289 NSC 2, dated 
January 26, 1995, and Boeing Service Bulletin Notice of Status 
Change 737-71-1289 NSC 03, dated October 3, 1996; is approved by the 
director of the Federal Register in accordance with 5 U.S.C. 552(a) 
and 1 CFR part 51.
    (2) The incorporation by reference of Boeing Service Bulletin 
737-71-1289, dated August 19, 1993, as listed in the regulations, 
was approved previously by the Director of the Federal Register as 
of May 18, 1994 (59 FR 18294, April 18, 1994).
    (3) 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.
    (h) This amendment becomes effective on January 24, 2000.

    Issued in Renton, Washington, on December 9, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-32509 Filed 12-17-99; 8:45 am]
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