Airworthiness Directives; Boeing Model 747 Series Airplanes

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 93-NM-183-AD; Amendment 39-8977; AD 94-15-06]

Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment supersedes 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 amendment requires inspection of an

expanded area, deletion of the reporting requirement, and expansion of

the applicability to include additional airplanes. This amendment is

prompted by reports of cracking of the fuselage skin in certain areas

and findings of additional countersunk fasteners. The actions specified

by this AD are intended to prevent reduced structural integrity of the

fuselage.

DATES: Effective August 24, 1994.

The incorporation by reference of certain publications listed in

the regulations is approved by the Director of the Federal Register as

of August 24, 1994.

ADDRESSES: The service information referenced in this AD may be

obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle,

Washington 98124-2207. This information may be examined at the Federal

Aviation Administration (FAA), Transport Airplane Directorate, Rules

Docket, 1601 Lind Avenue SW., Renton, Washington; or at the Office of

the Federal Register, 800 North Capitol Street, NW., suite 700,

Washington, DC.

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: A proposal to amend part 39 of the Federal

Aviation Regulations (14 CFR part 39) by superseding AD 90-01-07,

amendment 39-6440 (55 FR 255, January 4, 1990), which is applicable to

certain Boeing Model 747 series airplanes, was published in the Federal

Register on February 3, 1994 (59 FR 5139). The action proposed to

require inspection of an expanded area, deletion of the reporting

requirement, and expansion of the applicability.

Interested persons have been afforded an opportunity to participate

in the making of this amendment. Due consideration has been given to

the comments received.

One commenter supports the proposed rule.

Two commenters request that proposed paragraph (e) be revised to

reduce the area of inspection to coincide with the area specified in

the service bulletin (Boeing Service Bulletin 747-53A2312, Revision 2,

dated October 8, 1992) referenced in the proposal as the appropriate

source of service information. The FAA does not concur. An FAA

investigation has revealed that countersunk fasteners may be installed

in areas other than those specified in the referenced service bulletin.

Therefore, the FAA has determined that a one-time inspection along the

entire lap joint of the skin panel must be accomplished to positively

confirm the exact location of these countersunk fasteners.

One commenter requests an extension to the proposed compliance time

of 11,000 total landings to conduct the high frequency eddy current

(HFEC) inspection required by paragraph (g) of the proposal. The

commenter states that the compliance time should coincide with the time

recommended in the service bulletin (Boeing Service Bulletin 747-

53A2312, Revision 2, dated October 8, 1992) referenced in the proposal

as the appropriate source of service information. The compliance time

in the service bulletin specifies that, for airplanes on which only the

minimum number of countersunk fasteners have been installed, the HFEC

inspection should commence at 20,000 total flight cycles. The commenter

notes that for airplanes on which only the minimum number of

countersunk fasteners have been installed, the potential for widespread

multi-site damage is significantly lessened than for airplanes on which

more than the minimum number of countersunk fasteners have been

installed.

The FAA does not concur with the commenter's request to extend the

compliance time. In developing an appropriate compliance time for this

action, the FAA considered the safety implications of any cracking in

this area. The FAA acknowledges that cracking in the upper row of

countersunk fasteners in the lap splice in the area adjacent to the

wing-to-body fairing intersection may not result in catastrophic

consequences; however, the FAA finds that any cracking in this area has

the potential for developing into an unsafe condition. This AD is

issued to address that unsafe condition, which may result in reduced

structural integrity of the fuselage of the airplane as a result of

cracking in these areas. Further, since cracking has been found in this

area on in-service airplanes that had accumulated less than 20,000

total flight cycles, the FAA has determined that 11,000 total landings

represent the maximum interval of time allowable wherein the inspection

can reasonably be accomplished and an acceptable level of safety can be

maintained.

One commenter requests clarification of the proposed compliance

time for reinspection of previously modified lap joints. The commenter

requests that the HFEC inspections required by proposed paragraph (k)

commence from the time the lap joint was modified in accordance with AD

90-01-07, rather than from the time the lap joint is modified in

accordance with proposed paragraph (j). The FAA finds that

clarification is warranted. Paragraph (k) of the final rule has been

revised to state that HFEC inspections are to be performed prior to the

accumulation of 10,000 total landings following modifications (of

locations where countersunk fasteners were found) accomplished in

accordance with Boeing Service Bulletin 747-53A2312, dated June 12,

1989, Revision 1, dated March 29, 1990, or Revision 2, dated October 8,

1992, which includes modifications accomplished in accordance with AD

90-01-07 or in accordance with paragraph (j) of this AD.

Two commenters question the necessity for the inspections following

modification of the lap joints required by proposed paragraph (k). One

of these commenters does not see adequate justification for requiring

these inspections since AD 90-01-07 terminated the inspections after

accomplishment of the modification. The other commenter states that,

since other lap joints are not required to be inspected following

modification, this lap joint should not be inspected following

modification. From these comments, the FAA infers that these commenters

are requesting that the requirement to inspect following modification

be deleted. The FAA does not concur. An FAA evaluation of currently

available inspection techniques reveals that current technology may not

be able to adequately detect cracking beneath protruding head

fasteners. Further, in-service experience has demonstrated that

cracking has gone undetected beneath these protruding head fasteners.

Therefore, the FAA's intent in requiring these inspections following

the modification are to detect any cracking that may develop after

accomplishment of the modification and to repair any cracking prior to

it adversely affecting the structural integrity of the fuselage of the

airplane.

After careful review of the available data, including the comments

noted above, the FAA has determined that air safety and the public

interest require the adoption of the rule with the change previously

described. The FAA has determined that this change will neither

increase the economic burden on any operator nor increase the scope of

the AD.

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 will be affected by this AD.

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

retained in this AD, take approximately 14 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 $140,910, or $770 per

airplane, per inspection cycle.

The additional new inspections that are required by this AD will

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, per

inspection cycle.

The modification required by this AD will take approximately 124

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

per work hour. Required parts will 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.

The total cost impact figure discussed above is based on

assumptions that no operator has yet accomplished any of the

requirements of this AD action, and that no operator would accomplish

those actions in the future if this AD were not adopted.

The FAA recognizes that the modification will require a large

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

compliance time specified in paragraph (j) of this AD should allow

ample time for the modification of all countersunk fasteners locations

to be accomplished coincidentally with scheduled major airplane

inspection and maintenance activities, thereby minimizing the costs

associated with special airplane scheduling.

The regulations adopted herein will 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 final

rule does not have sufficient federalism implications to warrant the

preparation of a Federalism Assessment.

For the reasons discussed above, I certify that this action (1) is

not a ``significant regulatory action'' under Executive Order 12866;

(2) is not a ``significant rule'' under DOT Regulatory Policies and

Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action

and it is contained in the Rules Docket. A copy of it may be obtained

from the Rules Docket at the location provided under the caption

ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by

reference, Safety.

Adoption of the Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration amends 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. 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), amendment 39- , to read as follows:

94-15-06 BOEING: Amendment 39-8977. 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 total 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 during the inspections required

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

AD, no further action is required by this AD.

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

lap splice during the inspection required by paragraph (e) of this

AD, 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), and (k) of this AD, at any location where a

countersunk fastener was found, repeat the inspection thereafter 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 in accordance with Boeing Service Bulletin 747-53A2312,

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

Revision 2, dated October 8, 1992, perform an HFEC inspection at all

locations where countersunk fasteners were found, and repeat this

inspection thereafter 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

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.

(n) The actions shall be done in accordance with Boeing Service

Bulletin 747-53A2312, including the ``ADDENDUM,'' Revision 2, dated

October 8, 1992. This incorporation by reference was approved by the

Director of the Federal Register in accordance with 5 U.S.C. 552(a)

and 1 CFR part 51. Copies may be obtained from Boeing Commercial

Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207.

Copies may be inspected at the FAA, Transport Airplane Directorate,

1601 Lind Avenue, SW., Renton, Washington; or at the Office of the

Federal Register, 800 North Capitol Street, NW., suite 700,

Washington, DC.

(o) This amendment becomes effective on August 24, 1994.

Issued in Renton, Washington, on July 13, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-17592 Filed 7-22-94; 8:45 am]

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