Airworthiness Directives; Boeing Model 737 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-148-AD]

RIN 2120-AA64

Airworthiness Directives; Boeing Model 737 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 certain Boeing Model 737 series

airplanes. This proposal would require repetitive ultrasonic

inspections to detect broken bolts that attach the terminal support

fittings to the upper part of the Body Station 1088 bulkhead, and

corrective actions, if necessary. This proposal also would require

eventual replacement of the existing bolts with new, improved bolts,

which, when accomplished, would terminate the requirements of the AD.

This proposal is prompted by reports that bolts that attach the

terminal support fittings to the upper part of the bulkhead were found

broken. The actions specified by the proposed AD are intended to

prevent such broken bolts, which could result in reduced structural

integrity of the vertical fin installation and possible loss of the

vertical fin.

DATES: Comments must be received by August 31, 1998.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-114,

Attention: Rules Docket No. 98-NM-148-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: Rick Kawaguchi, Aerospace Engineer,

Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle

Aircraft Certification Office, 1601 Lind Avenue, SW., Renton,

Washington 98055-4056; telephone (425) 227-1153; 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-148-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-148-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

The FAA has received reports indicating that broken bolts were

found in the terminal support fittings that attach the aft spar of the

vertical fin to the upper part of the bulkhead at Body Station 1088 on

Boeing Model 737 series airplanes. The broken bolts were made of H-11

steel alloy. Bolts made of such material are susceptible to stress

corrosion cracking. Such broken bolts, if not corrected, could result

in reduced structural integrity of the vertical fin installation, and

multiple broken bolts could result in loss of the vertical fin.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Service Bulletin 737-53-

1107, Revision 3, dated August 26, 1993; as revised by Notices of

Status Change 737-53-1107 NSC 3, dated June 9, 1994, and 737-53-1107

NSC 4, dated September 22, 1994; and Boeing Service Bulletin 737-53-

1107, Revision 4, dated February 8, 1996. These service bulletins

describe procedures for repetitive ultrasonic inspections to detect

broken bolts that attach the terminal support fittings to the upper

part of the Body Station 1088 bulkhead, and replacement of the existing

bolts with new, improved bolts. The replacement includes removing the

bolts, performing an eddy current inspection to detect cracking or

corrosion of the bolt holes, oversizing the bolt holes, and installing

new Inconel bolts. Installation of the new Inconel bolts would

eliminate the need for the repetitive inspections described previously.

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 accomplishment of the actions specified in

the service bulletins and notices of status change described

previously, except as discussed below.

Differences Between Proposed Rule and Service Bulletin

Operators should note that, although the service bulletins specify

that the

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manufacturer may be contacted for disposition of certain repair

conditions, this proposal would require the repair of those conditions

to be accomplished in accordance with a method approved by the FAA.

Cost Impact

There are approximately 1,485 airplanes of the affected design in

the worldwide fleet. The FAA estimates that 630 airplanes of U.S.

registry would be affected by this proposed AD.

It would take approximately 3 work hours per airplane to accomplish

the proposed inspection, at an average labor rate of $60 per work hour.

Based on these figures, the cost impact of the inspection proposed by

this AD on U.S. operators is estimated to be $113,400, or $180 per

airplane, per inspection cycle.

It would take approximately 9 work hours per airplane to accomplish

the proposed replacement, at an average labor rate of $60 per work

hour. Required parts would cost approximately $471 per airplane. Based

on these figures, the cost impact of the replacement proposed by this

AD on U.S. operators is estimated to be $636,930, or $1,011 per

airplane.

The cost impact figures discussed above are 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.

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-148-AD.

Applicability: Model 737 series airplanes, line numbers 1

through 1485 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

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 (c) 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 broken bolts that attach the terminal support

fittings to the upper part of the Body Station (BS) 1088 bulkhead,

which could result in reduced structural integrity of the vertical

fin installation and possible loss of the vertical fin, accomplish

the following:

(a) Within 18 months after the effective date of this AD,

perform an ultrasonic inspection to detect broken bolts that attach

the terminal support fittings to the upper part of the BS 1088

bulkhead, in accordance with Boeing Service Bulletin 737-53-1107,

Revision 3, dated August 26, 1993; as revised by Notice of Status

Change 737-53-1107 NSC 3, dated June 9, 1994, and Notice of Status

Change 737-53-1107 NSC 4, dated September 22, 1994; or Boeing

Service Bulletin 737-53-1107, Revision 4, dated February 8, 1996.

(1) If no broken bolt is found, repeat the ultrasonic inspection

thereafter at intervals not to exceed 18 months.

(2) If any broken bolt is found, prior to further flight,

perform the actions specified in paragraph (b) of this AD.

(b) Prior to the accumulation of 20 years since date of

manufacture of the airplane, or within 18 months after the effective

date of this AD, whichever occurs later, remove all 16 H-11 steel

alloy bolts that attach the terminal support fittings to the upper

part of the bulkhead, and perform an eddy current inspection to

detect cracking or corrosion of the bolt holes, in accordance with

Figure 2 of Boeing Service Bulletin 737-53-1107, Revision 3, dated

August 26, 1993; as revised by Notice of Status Change 737-53-1107

NSC 3, dated June 9, 1994, and Notice of Status Change 737-53-1107

NSC 4, dated September 22, 1994; or Boeing Service Bulletin 737-53-

1107, Revision 4, dated February 8, 1996.

(1) If no cracking or corrosion is found, prior to further

flight, oversize all 16 bolt holes and install new Inconel bolts, in

accordance with Figure 2 of the service bulletin. Accomplishment of

this installation constitutes terminating action for the repetitive

inspection requirements of this AD.

(2) If any corrosion is found, prior to further flight, oversize

the bolt hole within the limits specified in Figure 2, Step 4, of

the service bulletin, and install a new Inconel bolt, in accordance

with Figure 2 of the service bulletin. Accomplishment of the

installation for all 16 bolt holes constitutes terminating action

for the repetitive inspection requirements of this AD. If corrosion

does not clean up within the limits specified in Figure 2, Step 4,

of the service bulletin, prior to further flight, repair in

accordance with a method approved by the Manager, Seattle Aircraft

Certification Office (ACO), FAA, Transport Airplane Directorate.

(3) If any cracking is found, prior to further flight, oversize

the bolt hole within the limits specified in Figure 2, Step 5, of

the service bulletin, and perform another eddy current inspection to

ensure cracks have been removed, in accordance with Figure 2 of the

service bulletin.

(i) If, after oversizing, no cracking is found, prior to further

flight, oversize the bolt hole again, and install a new Inconel

bolt, in accordance with Figure 2 of the service bulletin.

Accomplishment of the installation for all 16 bolt holes constitutes

terminating action for the repetitive inspection requirements of

this AD.

(ii) If, after oversizing, any cracking is found, prior to

further flight, repair in accordance with a method approved by the

Manager, Seattle ACO.

Note 2: Replacement of all H-11 steel alloy bolts accomplished

prior to the effective date of this AD, in accordance with Boeing

Service Bulletin 737-53-1107, dated October 15, 1987; Revision 1,

dated June 22, 1989; or Revision 2, dated September 10, 1992; is

considered acceptable for compliance with the applicable actions

specified in paragraph (b) of this AD.

(c) 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.

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Note 3: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Seattle ACO.

(d) 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 July 8, 1998.

S.R. Miller,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 98-18779 Filed 7-14-98; 8:45 am]

BILLING CODE 4910-13-U