Airworthiness Directives; Boeing Model 747 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 93-NM-183-AD]

Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing

airworthiness directive (AD), applicable to certain Boeing Model 747

series airplanes, that currently requires inspecting to detect cracking

in certain lower lobe lap joints, and repair, if necessary; reporting

any findings of discrepancies; replacing certain countersunk fasteners

with protruding head fasteners; and verifying that the airplanes do not

have certain countersunk fasteners. This action would increase the area

to be inspected, delete the reporting requirement, and expand the

applicability. This proposal is prompted by reports of fuselage skin

cracking in certain areas and findings of additional countersunk

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

prevent reduced structural integrity of the fuselage.

DATES: Comments must be received by March 30, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-103,

Attention: Rules Docket No. 93-NM-183-AD, 1601 Lind Avenue, SW.,

Renton, Washington 98055-4056. Comments may be inspected at this

location between 9 a.m. and 3 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: Steven C. Fox, Aerospace Engineer,

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

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

Washington 98055-4056; telephone (206) 227-2777; fax (206) 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 93-NM-183-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-103, Attention: Rules

Docket No. 93-NM-183-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

On December 19, 1989, the FAA issued AD 90-01-07, Amendment 39-6440

(55 FR 255, January 4, 1990), applicable to Boeing Model 747 series

airplanes, having line numbers 201 through 765, inclusive, to require:

1. Repetitively inspecting to detect cracking in certain lower lobe

lap joints, and repair, if necessary;

2. Reporting any findings of discrepancies;

3. Replacing certain countersunk fasteners with protruding head

fasteners; and

4. Verifying that airplanes do not have certain countersunk

fasteners.

That action was prompted by reports of cracking in the lap joint of

stringer 34 near the interface with the wing-to-body fairing. The

requirements of that AD are intended to prevent in-flight

depressurization due to undetected cracks in the skin of the airplane.

Since the issuance of that AD, the FAA has received additional

reports of cracking in the upper row of countersunk fasteners in the

lap splice in the area adjacent to the wing-to-body fairing

intersection on Model 747 series airplanes. Additionally, several

airplanes were found to have more than the necessary number of

countersunk fasteners, which were installed during production at the

upper row of the lap splice at stringer 34. These countersunk fasteners

were found in the upper row of fasteners in the lap splice near the

wing-to-body fairing and skin intersection between body station (BS)

768 and the circumferential skin joint at BS 741.

Cracking in locations where countersunk fasteners were installed,

if not corrected, could result in reduced structural integrity of the

fuselage.

The FAA has reviewed and approved Boeing Service Bulletin 747-

53A2312, Revision 2, dated October 8, 1992, that describes procedures

for visually inspecting to determine the number of countersunk

fasteners in the upper row of the lap splice.

If more than the necessary number of countersunk fasteners were

installed during production, this service bulletin specifies conducting

an external high frequency eddy current (HFEC) inspection to detect

cracking in the skin lap splices at the wing-to-body fairing

intersection where countersunk fasteners were found in the upper row of

fasteners. If cracking is found, the service bulletin describes

procedures for modifying the locations where countersunk fasteners were

found by replacing the countersunk fasteners with oversized protruding

head fasteners and repairing the skin. These actions were accomplished,

prior to delivery, on airplanes having line numbers 815 through 919,

inclusive.

If the proper number of countersunk fasteners were installed during

production, repetitive inspections are specified in the service

bulletin until the locations where countersunk fasteners were installed

have been modified.

The service bulletin describes procedures for eventual modification

of all airplanes at the location where countersunk fasteners were

installed, and repetitive inspections following modification.

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 supersede AD 90-01-07 to:

1. Continue to require inspections to detect cracking in certain

lower lobe lap joints, and repair, if necessary;

2. Require visual inspections to determine if countersunk fasteners

had been installed between body stations (BS) 741 and 1000 at Stringers

(S-)34L, S-34R, S-39L, S-39R, and S-44L, S-44R, and between BS 1480 and

1741 at S-34L, S-34R, S-40L, and S-40R on airplanes having line numbers

201 through 814, inclusive;

3. Require HFEC inspections to detect cracking at all locations

where countersunk fasteners were found in the upper row of the lap

splice, and repair, if necessary; and

4. Require modification of all locations where countersunk

fasteners were found.

Although the actions and compliance times of this proposed AD would

differ from the manufacturer's recommendations specified in the service

bulletin, the actions themselves would be required to be accomplished

in accordance with the procedures of the service bulletin described

previously.

There are approximately 723 Boeing Model 747 series airplanes of

the affected design in the worldwide fleet. The FAA estimates that 183

airplanes of U.S. registry would be affected by this AD.

The inspections that were previously required by AD 90-01-07, and

retained in this AD, take approximately 14 workhours per airplane to

accomplish, at an average labor rate of $55 per work hour. Based on

these figures, the total cost impact of these inspection requirements

of this AD on U.S. operators is estimated to be $140,910 or $770 per

airplane, per inspection cycle.

The additional new inspections that would be required by this AD

would take approximately 82 work hours per airplane to accomplish, at

an average labor rate of $55 per work hour. Based on these figures, the

total cost impact of these inspection requirements of this AD on U.S.

operators is estimated to be $825,330, or $4,510 per airplane

The modification required by this AD would take approximately 124

work hours per airplane to accomplish, at an average labor rate of $55

per work hour. Required parts would be nominal in cost. Based on these

figures, the total cost impact of the modification requirements of this

AD on U.S. operators is estimated to be $1,248,060, or $6,820 per

airplane.

Based on the above figures, the total cost impact of the inspection

and modification requirements of this AD on U.S. operators is estimated

to be $2,214,300, or $11,407 per airplane. This total cost figure

assumes that no operator has yet accomplished the proposed requirements

of this AD action.

The FAA recognizes that the proposed modification would require a

large number of work hours to accomplish. However, the 20,000-flight

cycle compliance time specified in paragraph (j) of this proposed AD

should allow ample time for the modification of all locations where

countersunk fasteners were found to be accomplished coincidentally with

scheduled major airplane inspection and maintenance activities, thereby

minimizing the costs associated with special airplane scheduling.

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 14

CFR part 39 of the Federal Aviation Regulations as follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C.

106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by removing amendment 39-6440 (55 FR

255, January 4, 1990), and by adding a new airworthiness directive

(AD), to read as follows:

Boeing: Docket 93-NM-183-AD. Supersedes AD 90-01-07, Amendment 39-

6440.

Applicability: Model 747 series airplanes, having line numbers

201 through 814 inclusive, certificated in any category.

Compliance: Required as indicated, unless accomplished

previously.

To prevent reduced structural integrity of the fuselage,

accomplish the following:

Restatement of Requirements of AD 90-01-07, Amendment 39-6440

(a) For airplanes having line numbers 201 through 765: Conduct a

high frequency eddy current (HFEC) inspection to detect cracking of

the lower lobe lap joints in the vicinity of the wing-to-body

fairing in accordance with Boeing Alert Service Bulletin 747-

53A2312, dated June 12, 1989; or Revision 1, dated March 29, 1990;

or Revision 2, dated October 8, 1992; at the time specified in

paragraph (a)(1), (a)(2), (a)(3), or (a)(4) of this AD, as

applicable. Repeat this inspection thereafter at intervals not to

exceed 4,000 landings until the inspection required by paragraph (e)

of this AD is accomplished.

(1) For airplanes that have accumulated less than 11,200 total

landings as of February 5, 1990 (the effective date of AD 90-01-07):

Prior to the accumulation of 11,000 landings or within the next

1,000 landings after February 5, 1990, whichever occurs later.

(2) For airplanes that have accumulated 11,200 or more total

landings but less than 15,201 total landings as of February 5, 1990

(the effective date of AD 90-01-07): Within the next 1,000 landings

after February 5, 1990, or prior to the accumulation of 15,500 total

landings, whichever occurs earlier.

(3) For airplanes that have accumulated 15,201 or more total

landings but less than 18,200 total landings as of February 5, 1990:

Within the next 300 landings after February 5, 1990, or prior to the

accumulation of 18,250 total landings, whichever occurs earlier.

(4) For airplanes that have accumulated 18,200 or more landings

as of February 5, 1990: Within the next 50 landings after February

5, 1990.

(b) For airplanes having line numbers 201 through 765:

Accomplish the requirements of paragraphs (b)(1) and (b)(2) of this

AD.

(1) If any cracking is detected, prior to further flight, repair

in accordance with Boeing Alert Service Bulletin 747-53A2312, dated

June 12, 1989; or Revision 1, dated March 29, 1990; or Revision 2,

dated October 8, 1992.

(2) Prior to the accumulation of 20,000 total landings or within

the next 3,000 landings after February 5, 1990 (the effective date

of AD 90-01-07), whichever occurs later, modify the airplane by

replacing countersunk fasteners in the upper row of the lower lobe

lap joints in the vicinity of the wing-to-body fairing with

protruding head fasteners, in accordance with the procedures

described in the Boeing Alert Service Bulletin 747-53A2312, dated

June 12, 1989; or Revision 1, dated March 29, 1990; or Revision 2,

dated October 8, 1992.

(c) For purposes of complying with paragraphs (a) and (b) of

this AD, the number of landings may be determined to equal the

number of pressurization cycles where the cabin pressure

differential was greater than 2.0 p.s.i.

(d) For Model 747SR airplanes only: Based on continued mixed

operation of lower cabin differentials, the inspection and

modification compliance times specified paragraphs (a) and (b) of

this AD may be multiplied by a 1.2 adjustment factor.

New Requirements of This AD

(e) Prior to the accumulation of 11,000 total landings, or

within 1,000 landings after the effective date of this AD, whichever

occurs later, unless previously accomplished within the last 3,000

landings prior to the effective date of this AD, conduct a visual

inspection to determine if countersunk fasteners have been installed

in the area defined in either paragraph (e)(1) or (e)(2), as

applicable, in accordance with the procedures described in Boeing

Service Bulletin 747-53A2312, Revision 2, dated October 8, 1992.

Accomplishment of this inspection terminates the inspection

requirements of paragraph (a) of this AD.

(1) For Model 747-100, -200, -300, -400, and 747SR series

airplanes: From body stations (BS) 741 to 1000 at Stringers (S-)34L,

S-34R, S-39L, S-39R, S-44L, and S-44R, and from BS 1480 to 1741 at

S-34L, S-34R, S-40L, and S-40R.

(2) For Model 747SP series airplanes: From BS 520 to 1000 at S-

34L, S-34R, S-39L, S-39R, S-44L, and S-44R, and from BS 1480 to 1741

at S-34L, S-34R, S-40L, and S-40R.

(f) If no countersunk fastener is found in the upper row of the

lap splice, no further action is required by this AD.

(g) If any countersunk fastener is found in the upper row of the

lap splice, prior to further flight, perform an HFEC inspection to

detect cracking at all locations where countersunk fasteners were

found, in accordance with the procedures described in Boeing Service

Bulletin 747-53A2312, Revision 2, dated October 8, 1992.

(h) If no cracking is detected during any inspection required by

paragraphs (g), (h), (i), and (k) of this AD, at any location where

a countersunk fastener was found, thereafter repeat the inspection

at intervals not to exceed 4,000 landings, in accordance with the

procedures described in the Boeing Service Bulletin 747-53A2312,

Revision 2, dated October 8, 1992.

(i) If cracking is detected during any inspection required by

paragraphs (g), (h), (i), and (k) of this AD, at any location where

a countersunk fastener was found, prior to further flight, repair

and modify that lap joint in accordance with Boeing Service Bulletin

747-53A2312, Revision 2, dated October 8, 1992.

(j) Prior to the accumulation of 20,000 total landings or within

1,000 landings after the effective date of this AD, whichever occurs

later, modify all locations where countersunk fasteners were found,

in accordance with the procedures described in Boeing Service

Bulletin 747-53A2312, Revision 2, dated October 8, 1992. For

purposes of complying with the requirements of this paragraph,

locations that were previously modified, in accordance with

paragraph (b) of this AD, do not need to be modified again.

(k) Prior to the accumulation of 10,000 total landings following

modification of the locations where countersunk fasteners were

installed, perform an HFEC inspection at all locations where

countersunk fasteners were found, and thereafter, repeat this

inspection at intervals not to exceed 4,000 landings, in accordance

with the procedures described in Boeing Service Bulletin 747-

53A2312, Revision 2, dated October 8, 1992.

(l) 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: Information concerning the existence of approved

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

obtained from the Seattle ACO.

(m) Special flight permits may be issued in accordance with FAR

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 January 28, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-2410 Filed 2-2-94; 8:45 am]

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