[Federal Register Volume 63, Number 222 (Wednesday, November 18, 1998)]
[Proposed Rules]
[Pages 64013-64016]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-30767]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-251-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, 
and -500 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 all Boeing Model 737-100, -200, -
300, -400, and -500 series airplanes. This proposal would require a 
one-time inspection of the main landing gear (MLG) wheel assemblies to 
determine whether certain parts are installed, and follow-on corrective 
actions, if necessary. For certain airplanes, this proposal also would 
require eventual modification of MLG wheel assemblies, which would 
terminate the requirements of this AD. This proposal is prompted by 
incidents of multiple tie bolt failures on certain BFGoodrich wheel 
assemblies. The actions specified by the proposed AD are intended to 
prevent failure of multiple tie bolts of MLG wheel assemblies, which 
could result in failure of the wheel rim, rapid release of tire 
pressure, and possible consequent damage to the airplane and injury to 
passengers and flightcrew.

DATES: Comments must be received by January 4, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-251-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 BFGoodrich Aerospace, Aircraft Wheels and Brakes, P.O. 
Box 340, Troy, Ohio 45373. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Don Kurle, Senior Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane 
Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, 
SW., Renton, Washington 98055-4056; telephone (425) 227-2798; 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 98-NM-251-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-251-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports indicating that tie bolts have failed 
on certain BFGoodrich wheel assemblies that are installed on the main 
landing gear (MLG) of Boeing Model 737-100, -200, -300, -400, and -500 
series airplanes. Most of the incidents of

[[Page 64014]]

failure of multiple tie bolts (that is, failure of more than one bolt 
on a single wheel) resulted only in flat tires. However, since 1989, 
there have been several incidents that resulted in high-energy release 
of the wheel rim and consequent damage to the airplane. In one 
incident, failure of both tires on the left MLG resulted in a rejected 
takeoff (RTO). Failure of the wheel tie bolts has been attributed to 
fatigue, which may be caused by improper torquing of the tie bolts. 
Although the specific cause of failure has not been identified on a few 
wheel tie bolts, other causes of failure have been identified as 
improper maintenance, wear, corrosion, or a combination of several 
factors. Failure of multiple wheel tie bolts, if not corrected, could 
result in failure of the wheel rim, rapid release of tire pressure, and 
possible consequent damage to the airplane and injury to passengers and 
flightcrew.

Explanation of Relevant Service Information

    The FAA has reviewed and approved BFGoodrich Aerospace Service 
Bulletins 3-1439-32-13 and 3-1398-32-16, both dated August 20, 1993. 
The service bulletins describe procedures for corrective actions if 
certain wheel assemblies are installed on the MLG. The corrective 
actions include modification of the wheel assembly by replacement of 
existing tie bolts, nuts, and washers with new, improved Inconel tie 
bolts and nuts, and new, thicker washers. The service bulletins also 
describe new torque values, procedures for inspecting the new tie bolts 
to ensure that they did not crack during torquing, and a procedure for 
stamping a new part number on the wheel assembly once it has been 
modified. Accomplishment of the actions specified in the service 
bulletins 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 a one-time visual inspection of the MLG wheel 
assemblies to determine whether certain part numbers are installed on 
the airplane, and follow-on corrective actions, if necessary.
    If certain part numbers are installed, the proposed AD would 
require repetitive replacement of all tie bolts, nuts, and washers of 
the MLG wheel assembly with new parts; or repetitive visual inspections 
to detect fractures of the tie bolts of the MLG wheel assembly, and 
replacement of discrepant parts with new parts. Alternatively, the 
proposed AD would require revisions to the FAA-approved maintenance 
program to require one of those actions. If those certain part numbers 
are installed, the proposed AD also would require eventual 
accomplishment of corrective actions specified in the service bulletins 
described previously, except as discussed below. Accomplishment of 
these corrective actions would terminate the requirements of this AD.

Differences Between Proposed Rule and Service Bulletins

    Operators should note that the service bulletins specify 
replacement of wheel tie bolts with new parts only when broken wheel 
tie bolts have been found. This proposed AD would require, at every 
fifth tire change, replacement of the existing wheel tie bolts, 
washers, and nuts with parts having the same part number, or repetitive 
visual inspections at intervals not to exceed 100 flight cycles; or 
alternatively, revisions to the FAA-approved maintenance program to 
require one of these actions.
    The service bulletins also specify that existing parts can continue 
to be used if there are no discrepancies in those parts. This proposed 
AD would require eventual modification of affected wheel assemblies by 
replacement of existing wheel tie bolts, washers, and nuts with new, 
improved parts, which would constitute terminating action for the 
requirements of this AD. The FAA has determined that long-term 
continued operational safety would be better assured by design changes 
to remove the source of the problem, rather than by repetitive 
inspections. Long-term inspections may not provide the degree of safety 
assurance necessary for the transport airplane fleet. This, coupled 
with a better understanding of the human factors associated with 
numerous continual inspections, has led the FAA to consider placing 
less emphasis on inspections and more emphasis on design improvements. 
The proposed modification is in consonance with these conditions.

Explanation of the Applicability of the Rule

    The FAA notes that its general policy is that, when an unsafe 
condition results from the installation of an appliance or other item 
that is installed in only one particular make and model of airplane, an 
AD is issued so that it is applicable to the airplane, rather than the 
item. The reason for this is simple: making the AD applicable to the 
airplane model on which the item is installed ensures that operators of 
those airplanes will be notified directly of the unsafe condition and 
the action required to correct it. While it is assumed that an operator 
will know the models of airplanes that it operates, there is a 
potential that the operator will not know or be aware of specific items 
that are installed on its airplanes. Therefore, calling out the 
airplane model as the subject of the AD prevents ``unknowing non-
compliance'' on the part of the operator.

Cost Impact

    There are approximately 460 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 118 airplanes of U.S. registry 
would be affected by this proposed AD.
    It would take approximately 1 work hour per airplane to accomplish 
the proposed one-time inspection, at an average labor rate of $60 per 
work hour. Based on these figures, the cost impact of the one-time 
inspection proposed by this AD on U.S. operators is estimated to be 
$7,080, or $60 per airplane.
    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 repetitive visual 
inspection, it would take approximately 1 work hour per airplane to 
accomplish, at an average labor rate of $60 per work hour. Based on 
these figures, the cost impact of the repetitive inspections, if 
accomplished, is estimated to be $60 per airplane, per inspection 
cycle.
    Should an operator elect to accomplish the replacement, such 
replacement would require no additional work hours if accomplished 
during a regularly scheduled tire change. Required parts would cost 
$2,840 per airplane ($710 per wheel). Based on these figures, the cost 
impact of the replacement, if accomplished, is estimated to be $2,840 
per airplane, per replacement cycle.
    Should an operator elect to accomplish the revisions to the FAA-
approved maintenance program, it would take approximately 1 work hour 
per airplane to accomplish, at an average labor rate of $60 per work 
hour. Based on these figures, the cost impact of the maintenance 
program revision, if accomplished, is estimated to be $60 per airplane.
    Should an operator be required to accomplish the necessary 
modification of the wheel assembly, it would require no additional work 
hours per airplane,

[[Page 64015]]

if the modification is accomplished during a regularly scheduled tire 
change. Required parts would cost $4,848 per airplane ($1,212 per 
wheel). Based on these figures, the cost impact of any necessary 
modification is estimated to be $4,848 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 98-NM-251-AD.
    Applicability: All Model 737-100, -200, -300, -400, and -500 
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 (e) 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.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent failure of multiple tie bolts of main landing gear 
(MLG) wheel assemblies, which could result in failure of the wheel 
rim, rapid release of tire pressure, and possible consequent damage 
to the airplane and injury to passengers and flightcrew, accomplish 
the following:
    (a) Within 60 days after the effective date of this AD, perform 
a one-time visual inspection of the MLG wheel assemblies to 
determine the part number (P/N) of each assembly. If no wheel 
assembly manufactured by BFGoodrich Aerospace and having P/N 3-1398-
1, 3-1439-2, or 3-1439-3 is installed on the airplane, no further 
action is required by this AD.
    (b) Except as provided by paragraph (d) of this AD, if any MLG 
wheel assembly manufactured by BFGoodrich Aerospace and having P/N 
3-1398-1, 3-1439-2, or 3-1439-3 is installed on the airplane, within 
60 days after the effective date of this AD, accomplish the actions 
specified by paragraph (b)(1) or (b)(2) of this AD.
    (1) Accomplish the actions specified by (b)(1)(i) or (b)(1)(ii) 
of this AD.
    (i) Replace all tie bolts, nuts, and washers of the MLG wheel 
assembly with parts having the same P/N's, in accordance with the 
BFGoodrich component maintenance manual. Thereafter, repeat the 
replacement of tie bolts, nuts, and washers, at intervals not to 
exceed 5 tire changes, until the actions specified by paragraph 
(b)(2) or paragraph (c) of this AD have been accomplished. Or
    (ii) Perform a visual inspection to detect fractures of any of 
the 16 tie bolts on each MLG wheel assembly, in accordance with the 
Boeing 737 airplane maintenance manual. Thereafter, repeat the 
inspection at intervals not to exceed 100 flight cycles until the 
actions specified by paragraph (b)(2) or paragraph (c) of this AD 
have been accomplished. If any fracture of any tie bolt is found 
during any inspection performed in accordance with this requirement, 
prior to further flight, replace the tie bolt, nut, and washer, in 
accordance with the BFGoodrich component maintenance manual, with 
new parts having the same P/N's.
    (2) Revise the FAA-approved maintenance program as specified in 
paragraph (b)(2)(i) or (b)(2)(ii) of this AD.
    (i) Revise the FAA-approved maintenance program to require 
replacement of all tie bolts, nuts, and washers of the MLG wheel 
assembly with parts having the same P/N's, in accordance with the 
BFGoodrich component maintenance manual, at intervals not to exceed 
5 tire changes. Or
    (ii) Revise the FAA-approved maintenance program to require a 
visual inspection to detect fractures of any of the 16 tie bolts on 
each MLG wheel assembly, in accordance with the Boeing 737 airplane 
maintenance manual, at intervals not to exceed 100 flight cycles. If 
any fracture of any tie bolt is found during any inspection 
performed in accordance with this requirement, prior to further 
flight, replace the tie bolt, nut, and washer, in accordance with 
the BFGoodrich component maintenance manual, with new parts having 
the same P/N's.

    Note 2: After the maintenance program has been revised to 
include the procedures specified in paragraph (b)(2)(i) or 
(b)(2)(ii) of this AD, operators are not required to subsequently 
record AD compliance each time the replacement or inspection is 
performed.

    (c) If any MLG wheel assembly manufactured by BFGoodrich 
Aerospace and having P/N 3-1398-1, 3-1439-2, or 3-1439-3 is 
installed on the airplane: Except as provided by paragraph (d) of 
this AD, within 2 years after the effective date of this AD, modify 
any BFGoodrich Aerospace wheel assembly, having P/N 3-1398-1, 3-
1439-2, or 3-1439-3; by replacing all existing tie bolts, nuts, and 
washers, with new, improved parts; and by converting the P/N of the 
MLG wheel assembly to 3-1398-2 (for BFGoodrich wheel assemblies 
having the old P/N 3-1398-1), 3-1439-5 (for BFGoodrich wheel 
assemblies having the old P/N 3-1439-2), or 3-1439-6 (for BFGoodrich 
wheel assemblies having the old P/N 3-1439-3), as applicable; in 
accordance with BFGoodrich Aerospace Service Bulletin 3-1439-32-13, 
or BFGoodrich Aerospace Service Bulletin 3-1398-32-16, both dated 
August 20, 1993, as applicable. Such modification constitutes 
terminating action for the requirements of this AD, and the FAA-
approved maintenance program procedures specified by paragraph 
(b)(2) of this AD may be removed following accomplishment of the 
requirements of this paragraph.
    (d) Airplanes on which the modification required by paragraph 
(c) of this AD is accomplished within the compliance time specified 
in paragraph (b) of this AD are not required to accomplish the 
actions required by paragraph (b).
    (e) 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 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (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.


[[Page 64016]]


    Issued in Renton, Washington, on November 10, 1998.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-30767 Filed 11-17-98; 8:45 am]
BILLING CODE 4910-13-P