Airworthiness Directives; Boeing Model 747-100, -200 and 747SP Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-339-AD]

RIN 2120-AA64

Airworthiness Directives; Boeing Model 747-100, -200 and 747SP

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 747-100, -200

and 747SP series airplanes. This proposal would require repetitive

detailed visual and ultrasonic inspections to detect missing, damaged,

or broken taperlock bolts in the diagonal brace underwing fittings; and

corrective actions, if necessary. This proposal also would require

eventual replacement of the aft 10 taperlock bolts with new bolts,

which would constitute terminating action for the repetitive

inspections. This proposal is prompted by reports of damaged, broken,

and corroded taperlock bolts of the diagonal brace underwing fittings

on the outboard strut due to stress corrosion cracking. The actions

specified by the proposed AD are intended to prevent loss of the

underwing fitting load path due to missing, damaged, or broken

taperlock bolts, which could result in separation of the engine and

strut from the airplane.

DATES: Comments must be received by October 15, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

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

Attention: Rules Docket No. 98-NM-339-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: Tamara L. Anderson, Aerospace

Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane

Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue,

SW., Renton, Washington 98055-4056; telephone (425) 227-2771; 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

[[Page 47441]]

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-339-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-339-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

The FAA has received reports indicating that damaged, broken, and

corroded taperlock bolts were found on Boeing Model 747-100 and -200

series airplanes. The cause of the broken taperlock bolts is stress

corrosion. The bolts are located on the diagonal brace underwing

fittings on the outboard strut at the Number 1 and Number 4 pylon

engine positions. This condition, if not corrected, could result in

separation of the engine and strut from the airplane.

The subject taperlock bolts on Boeing Model 747SP series airplanes

are identical to those on the affected Boeing Model 747-100 and -200

series airplanes. Therefore, all of these airplanes may be subjected to

the same unsafe condition.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletin

747-57A2308, dated August 6, 1998, which describes procedures for

repetitive detailed visual and ultrasonic inspections to detect

missing, damaged, or broken taperlock bolts; and corrective actions, if

necessary. The corrective actions involve performing an open hole high

frequency eddy current inspection to detect cracks at the bolt hole

locations; and replacing missing, damaged, or broken taperlock bolt

with a new bolt. This service bulletin also describes procedures for an

optional terminating action for the repetitive inspections.

Accomplishment of the actions specified in the service bulletin 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 bulletin described previously, except as discussed below.

Differences Between Proposed Rule and Service Bulletin

Operators should note that, although incorporation of the

terminating action specified in the referenced service bulletin is

optional, this AD proposes to mandate, within 48 months after the

effective date of this AD, the open hole inspection and replacement of

the aft 10 taperlock bolts with new bolts specified in the referenced

service bulletin as terminating action for the repetitive inspections.

The FAA has determined that long-term continued operational safety

will be better assured by design changes to remove the source of the

problem, rather than by repetitive inspections. Long-term inspections

may not be providing the degree of safety assurance necessary for the

transport airplane fleet. This, coupled with a better understanding of

the human factors associated with numerous continued inspections, has

led the FAA to consider placing less emphasis on inspections and more

emphasis on design improvements. The proposed replacement requirement

is in consonance with these conditions.

In addition, operators should note that, although the service

bulletin specifies that the manufacturer must be contacted for

disposition of certain conditions, this proposal would require the

repair of those conditions to be accomplished in accordance with a

method approved by the FAA; or in accordance with data meeting the type

certification basis of the airplane approved by a Boeing Company

Designated Engineering Representative who has been authorized by the

FAA to make such findings. For a method to be approved, the approval

letter must specifically reference this AD.

Cost Impact

There are approximately 274 airplanes of the affected design in the

worldwide fleet. The FAA estimates that 122 airplanes of U.S. registry

would be affected by this proposed AD, that it would take approximately

1 work hour 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 proposed inspection on U.S. operators is estimated

to be $7,320, or $60 per airplane, per inspection cycle.

It would take approximately 8 work hours per airplane to accomplish

the proposed terminating action, at an average labor rate of $60 per

work hour. Required parts would cost approximately $8,008 per airplane.

Based on these figures, the cost impact of the proposed terminating

action on U.S. operators is estimated to be $1,035,536, or $8,488 per

airplane.

The cost impact figures discussed above are based on the assumption

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.

[[Page 47442]]

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-339-AD.

Applicability: Model 747-100, -200, and 747SP series airplanes,

line numbers 1 through 567 inclusive; equipped with aluminum

diagonal brace underwing fittings; certificated in any category.

Note 1: This AD applies to each airplane identified in the

preceding applicability provision, regardless of whether it has been

otherwise 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 (f) 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 loss of the underwing fitting load path due to

missing, damaged, or broken taperlock bolts, which could result in

separation of the engine and strut from the airplane, accomplish the

following:

Repetitive Inspections

(a) Prior to the accumulation of 9,000 total flight cycles, or

within 18 months after the effective date of this AD, whichever

occurs later, accomplish the actions required by paragraphs (a)(1)

and (a)(2) of this AD in accordance with Boeing Alert Service

Bulletin 747-57A2308, dated August 6, 1998. Thereafter, repeat the

inspections at intervals not to exceed 18 months until

accomplishment of the actions specified in paragraph (d) of this AD.

(1) Perform a detailed visual inspection to detect missing

taperlock bolts in the diagonal brace underwing fitting at the

Number 1 and Number 4 pylons.

Note 2: For the purposes of this AD, a detailed visual

inspection is defined as: ``An intensive visual examination of a

specific structural area, system, installation, or assembly to

detect damage, failure, or irregularity. Available lighting is

normally supplemented with a direct source of good lighting at

intensity deemed appropriate by the inspector. Inspection aids such

as mirror, magnifying lenses, etc., may be used. Surface cleaning

and elaborate access procedures may be required.''

(2) Perform an ultrasonic inspection to detect damaged or broken

taperlock bolts in the diagonal brace underwing fitting at the

Number 1 and Number 4 pylons.

Corrective Actions

(b) If any missing, damaged, or broken taperlock bolt is

detected during any inspection required by paragraph (a) of this AD,

prior to further flight, perform the applicable corrective actions

(i.e., inspection, drill/ream, and replacement) in accordance with

Boeing Alert Service Bulletin 747-57A2308, dated August 6, 1998;

except as provided in paragraph (c) of this AD. Replacement of any

taperlock bolt with a new bolt in accordance with this paragraph

constitutes terminating action for the repetitive inspections

required by paragraph (a) of this AD for that bolt only.

(c) If any crack is detected during the inspection required by

paragraph (b) of this AD and the damage to a bolt hole exceeds first

oversize (for 0.5-inch bolts) or second oversize (for 0.4375-inch

bolts); and the service bulletin specifies to contact Boeing for

appropriate Action: Prior to further flight, repair in accordance

with a method approved by the Manager, Seattle Aircraft

Certification Office (ACO), FAA, Transport Airplane Directorate; or

in accordance with a Boeing Company Designated Engineering

Representative who has been authorized by the Manager, Seattle ACO,

to make such findings. For a repair method to be approved by the

Manager, Seattle ACO, as required by this paragraph, the Manager's

approval letter must specifically reference this AD.

Terminating Action

(d) Within 48 months after the effective date of this AD,

accomplish the actions required by paragraphs (d)(1) and (d)(2) of

this AD in accordance with Boeing Alert Service Bulletin 747-

57A2308, dated August 6, 1998. Accomplishment of the actions

specified in this paragraph constitutes terminating action for the

repetitive inspection requirements of this AD.

(1) Prior to accomplishing the replacement required by paragraph

(d)(2) of this AD, perform an open hole high frequency eddy current

inspection to detect cracks at the bolt hole locations of the aft 10

taperlock bolts. If any cracking is detected, prior to further

flight, perform applicable corrective actions in accordance with

paragraph (c) of this AD.

(2) Replace the aft 10 taperlock bolts with new bolts in the

diagonal brace underwing fitting at the Number 1 and Number 4

pylons.

Spares

(e) As of the effective date of this AD, no person shall install

a bolt, part number BACB30PE( ) * ( ), or any other bolt made of

4340, 8740, or PH13-8 Mo steel, in the locations specified in this

AD, on any airplane.

Alternate Method of Compliance

(f) 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.

Note 3: Information concerning the existence of approved

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

obtained from the Seattle ACO.

Special Flight Permits

(g) 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 August 24, 1999.

Vi L. Lipski,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 99-22529 Filed 8-30-99; 8:45 am]

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