Airworthiness Directives; Boeing Model 747 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-56-AD]

RIN 2120-AA64

Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

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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 series

airplanes. This proposal would require repetitive inspections or checks

to detect broken H-11 steel bolts at the wing rear spar side-of-body on

the lower chord splice plate and kick fitting; and corrective actions,

if necessary. This proposal also would require eventual replacement of

the existing bolts with new inconel bolts, which would constitute

terminating action for the repetitive inspections. This proposal is

prompted by a report of broken bolts at the wing rear spar side-of-body

on the lower chord splice plate. The actions specified by the proposed

AD are intended to prevent cracking of the bolts due to stress

corrosion, which could result in reduced structural integrity of the

wing-to-body joint structure.

DATES: Comments must be received by October 18, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

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

Attention: Rules Docket No. 99-NM-56-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. 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 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 99-NM-56-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. 99-NM-56-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

The FAA has received a report indicating that an operator found

four broken high strength H-11 steel bolts on a Boeing Model 747 series

airplane. The broken bolts were on one side of the wing rear spar side-

of-body on the lower chord splice plate. The broken bolts were

attributed to stress corrosion cracking. This condition, if not

detected, could result in reduced structural integrity of the wing-to-

body joint structure.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletin

747-57A2309, dated February 25, 1999. The service bulletin describes

procedures for repetitive detailed visual inspections, or

alternatively, ultrasonic inspections or torque checks, to detect

broken H-11 steel bolts common to the rear spar lower chord splice

plate and H-11 steel bolts on the wing rear spar lower kick fitting;

and corrective actions, if necessary. The corrective actions involve

performing either an ultrasonic inspection or torque check for broken

bolts, if necessary; an open hole high frequency eddy current (HFEC)

inspection to detect cracks at the broken bolt hole location; and

installing an inconel bolt, which would eliminate the need for the

repetitive inspections at this bolt location, as applicable. The

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

specified in the referenced service bulletin as terminating action for

the repetitive inspections.

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 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 continual 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 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, 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 repair method to be approved, the

approval letter must specifically reference this AD.

Cost Impact

There are approximately 523 airplanes of the affected design in the

worldwide fleet. The FAA estimates that

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115 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 inspection of the wing

rear spar side-of-body lower chord splice plate and kick fitting high

strength H-11 steel bolts proposed by this AD on U.S. operators is

estimated to be $6,900, or $60 per airplane, per inspection cycle.

It would take approximately 13 (Groups 1, 3, 4, and 5 airplanes)

and 10 (Group 2 airplanes) work hours per airplane to accomplish the

proposed open hole HFEC inspection and replacement, at an average labor

rate of $60 per work hour. Required parts would cost approximately

$4,500 per airplane. Based on these figures, the cost impact of the

open hole HFEC inspection and replacement proposed by this AD on U.S.

operators is estimated to be $5,280 (Groups 1, 3, 4, and 5 airplanes)

and $5,100 (Group 2 airplanes) 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 99-NM-56-AD.

Applicability: Model 747 series airplanes, as listed in Boeing

Alert Service Bulletin 747-57A2309, dated February 25, 1999,

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 (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 detect and prevent cracking of the high strength H-11 steel

bolts on the wing rear spar side-of-body on the lower chord splice

plate and kick fitting due to stress corrosion, which could result

in reduced structural integrity of the wing-to-body joint structure,

accomplish the following:

Repetitive Inspections

(a) Within 12 months after the effective date of this AD,

perform a detailed visual inspection, or alternatively, an

ultrasonic inspection or torque check, to detect broken H-11 steel

bolts common to the rear spar lower chord splice plate and the H-11

steel bolts common to the wing rear spar lower chord kick fitting,

in accordance with Boeing Alert Service Bulletin 747-57A2309, dated

February 25, 1999. Thereafter, repeat the applicable inspection or

torque check at intervals not to exceed 18 months, until

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

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

Corrective Actions

(b) If there is any detection or indication that any bolt is

broken during the inspection required by paragraph (a) of this AD,

prior to further flight, perform the applicable corrective action

[i.e., ultrasonic inspection, torque check, high frequency eddy

current (HFEC) inspection, repair, and replacement] in accordance

with Boeing Alert Service Bulletin 747-57A2309, dated February 25,

1999; except as provided in paragraph (c) of this AD. Replacement of

a broken bolt with a new inconel bolt in accordance with the service

bulletin constitutes terminating action for the repetitive

inspection requirements of paragraph (a) of this AD for that bolt

only.

(c) If any crack is detected during any corrective action

required by paragraph (b) of this AD; 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 data meeting the type

certification basis of the airplane approved by 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-

57A2309, dated February 25, 1999. 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 HFEC inspection to detect

cracks at the bolt hole location for the eight high strength H-11

steel bolts common to the rear spar lower chord splice plate and the

four high strength H-11 steel bolts common to the wing rear spar

lower chord kick fitting. If any crack is detected, prior to further

flight, perform applicable corrective actions in accordance with

paragraph (c) of this AD.

(2) Replace all eight high strength H-11 steel bolts common to

the rear spar lower chord splice plate and all four high strength H-

11 steel bolts common to the wing rear spar lower chord kick fitting

with new inconel bolts.

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Spares

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

an H-11 steel bolt having part number (P/N) BACB30MT ( ) * ( ) or

BACB30TR ( ) * ( ), or any other H-11 steel bolt in the locations

specified in this AD, on any airplane.

Alternative Methods 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

Secs. 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 27, 1999.

Vi L. Lipski,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 99-22921 Filed 9-1-99; 8:45 am]

BILLING CODE 4910-13-P