[Federal Register Volume 62, Number 80 (Friday, April 25, 1997)]
[Proposed Rules]
[Pages 20132-20135]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-10787]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 96-NM-245-AD]
RIN 2120-AA64


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 adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 747 series 
airplanes. This proposal would require an internal visual inspection to 
detect cracks of the skin and internal doublers above main entry door 1 
at body station 460, and various follow-on actions. This proposal is 
prompted by reports indicating that multiple fatigue cracks were found 
in both internal skin doublers. The actions specified by the proposed 
AD are intended to detect and correct such fatigue cracking, which 
could result in reduced structural integrity of the fuselage and 
consequent rapid depressurization of the cabin.

DATES: Comments must be received by June 6, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-245-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.

[[Page 20133]]

    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: Bob Breneman, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2776; 
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 96-NM-245-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. 96-NM-245-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received a report of multiple cracks in both internal 
skin doublers of a Boeing Model 747 series airplane that had 
accumulated 24,723 flight cycles. These cracks extended under the outer 
flange of the frame at body station (STA) 460 for a maximum of 13 
inches. The FAA received additional reports of cracking of the internal 
doublers; one of these reports involved an airplane that had 
accumulated only 13,517 flight cycles. Results of full-scale fatigue 
tests on Model 747 test articles revealed similar cracks in the 
internal skin doublers. Such cracking has been attributed to structural 
fatigue. Fatigue cracking in the internal doublers, if not detected and 
corrected in a timely manner, could result in reduced structural 
integrity of the fuselage and consequent rapid depressurization of the 
cabin.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 747-
53A2396, Revision 1, dated February 22, 1996, which describes 
procedures for performing an internal visual inspection to detect 
cracks of the skin and internal doublers above main entry door 1 at STA 
460, and various follow-on actions. The follow-on actions include:
    1. An open hole high frequency eddy current (HFEC) inspection to 
detect cracks of the skin and internal doublers above main entry door 
1, and repair, if necessary;
    2. Installation of an external doubler;
    3. A visual inspection to detect damage of the adjacent structure 
within 20 inches of detected cracks, and repair, if necessary; and
    4. Repetitive internal surface HFEC inspections or external low 
frequency eddy current (LFEC) inspections to detect damage of repaired 
or modified areas.

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 an internal visual inspection to detect 
cracks of the skin and internal doublers above main entry door 1 at STA 
460, and various follow-on actions. The actions would be required to be 
accomplished in accordance with the service bulletin described 
previously. If any damage is detected in repaired or modified areas, a 
repair would be required to be accomplished in accordance with a method 
approved by the FAA.

Differences Between Proposed AD and Relevant Service Information

    Operators should note that the referenced service bulletin 
specifies a provision that cabin differential pressurization cycles of 
2.0 pounds per square inch (psi) or less need not be counted as a 
flight cycle when determining the number of flight cycles relative to 
the proposed compliance thresholds. This proposed AD does not include 
such a provision. In several AD's in the past, the FAA considered that 
flights with less than 2.0 psi cabin differential pressure contributed 
to a negligible amount of fatigue damage to the fuselage structure; 
thus, the FAA allowed the use of the subject provision in those AD's. 
However, the FAA has received new data indicating that discounting 
cabin differential pressurization cycles of 2.0 psi or less is not 
conservative, and does not provide an accurate determination of 
equivalent flight cycles.
    Operators of Boeing Model 747SR series airplanes should also note 
that, unlike the procedures described in the referenced service 
bulletin, this proposed AD would not permit the 1.2 adjustment factor 
to be used to reduce the inspection threshold. In several AD's in the 
past, the FAA allowed the use of this adjustment factor. However, based 
on new data, the FAA has determined that the 1.2 adjustment factor 
would not address the unsafe condition in a timely manner. The FAA may 
consider additional rulemaking to address all previously issued AD's 
applicable to Boeing Model 747 series airplanes that allow the use of 
the 1.2 adjustment factor.

Other Relevant Rulemaking

    The FAA has previously issued two other AD's that concern the area 
above the main entry doors on Boeing Model 747 series airplanes having 
line numbers prior to 207:
    1. AD 89-21-09, amendment 39-6350 (54 FR 41053, October 5, 1989), 
requires periodic inspection of the fuselage skin just above the 
forward main entry door for cracks emanating from the circumferential 
skin splice, and modifications, if necessary.
    2. AD 90-06-06, amendment 39-6490 (55 FR 8374, March 7, 1990), 
requires incorporation of certain structural modifications.
    However, this proposed AD would not affect the current requirements 
of any of those previously issued AD's.

Cost Impact

    There are approximately 880 Boeing Model 747 series airplanes of 
the affected design in the worldwide fleet. The FAA estimates that 143 
airplanes of U.S. registry would be affected by this proposed AD. Each 
of these airplanes has a left and right-side main entry door 1.

[[Page 20134]]

    It would take approximately 76 work hours per airplane to 
accomplish the proposed internal visual inspection, at an average labor 
rate of $60 per work hour. Based on these figures, the cost impact of 
the internal visual inspection proposed by this AD on U.S. operators is 
estimated to be $652,080, or $4,560 per airplane.
    Should an operator be required to accomplish the proposed 
preventative modification, it would take approximately 100 work hours 
per airplane to accomplish, at an average labor rate of $60 per work 
hour. Required parts would cost approximately $1,094 per airplane. 
Based on these figures, the cost impact of the installation proposed by 
this AD on U.S. operators is estimated to be $1,014,442, or $7,094 per 
airplane.
    It would take approximately 40 work hours per airplane to 
accomplish the proposed HFEC or LFEC inspection (i.e., post-
modification), at an average labor rate of $60 per work hour. Based on 
these figures, the cost impact of the HFEC or LFEC inspection proposed 
by this AD on U.S. operators is estimated to be $343,200, or $2,400 per 
airplane, per inspection cycle.
    Should an operator be required to accomplish the proposed repair, 
it would take approximately 212 work hours per airplane to accomplish, 
at an average labor rate of $60 per work hour. Required parts would 
cost approximately $2,602 per airplane. Based on these figures, the 
cost impact of the repair proposed by this AD on U.S. operators is 
estimated to be $2,191,046, or $15,322 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 96-NM-245-AD.

    Applicability: Model 747 series airplanes, having line number 
207 through 1088 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 (e) 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 correct fatigue cracking in the internal skin 
doublers, which could result in reduced structural integrity of the 
fuselage and consequent rapid depressurization of the cabin, 
accomplish the following:
    (a) For airplanes identified as Groups 1 through 10, inclusive, 
in Boeing Service Bulletin 747-53A2396, Revision 1, dated February 
22, 1996: Prior to the accumulation of 13,000 flight cycles, or 
within 18 months after the effective date of this AD, whichever 
occurs later, perform an internal visual inspection to detect cracks 
of the skin and internal doublers above main entry door 1 at body 
station (STA) 460, in accordance with Part 2--Inspection of the 
Accomplishment Instructions of Boeing Service Bulletin 747-53A2396, 
Revision 1, dated February 22, 1996.
    (1) If no crack is detected during the internal visual 
inspection required by paragraph (a) of this AD, prior to further 
flight, perform an open hole high frequency eddy current (HFEC) 
inspection to detect cracks of the skin and internal doublers above 
main entry door 1, in accordance with Figure 10 of the service 
bulletin.
    (i) If no crack is detected during the open hole HFEC inspection 
required by paragraph (a)(1) of this AD, prior to further flight, 
install an external doubler in accordance with Part 4--Modification 
of the Accomplishment Instructions of the service bulletin.
    (ii) If any crack is detected during the open hole HFEC 
inspection, prior to further flight, perform a visual inspection to 
detect damage of the adjacent structure within 20 inches of the 
cracks, in accordance with Part 3--Repair of the Accomplishment 
Instructions of the service bulletin. If any damage is detected, 
prior to further flight, repair it in accordance with Part 3--
Repair, or the NOTE specified in paragraph G. of Part 2--Inspection 
of the Accomplishment Instructions of the service bulletin.
    (2) If any crack is detected during the internal visual 
inspection required by paragraph (a) of this AD, prior to further 
flight, perform a visual inspection to detect damage of the adjacent 
structure within 20 inches of the cracks, in accordance with Part 
3--Repair of the Accomplishment Instructions of the service 
bulletin. Prior to further flight following accomplishment of this 
visual inspection, repair any cracked skin or internal doublers, 
and/or repair adjacent damaged structure, in accordance with Part 
3--Repair of the Accomplishment Instructions of the service 
bulletin.
    (b) Perform either an internal surface HFEC or external low 
frequency eddy current (LFEC) inspection to detect damage of the 
repaired or modified area, in accordance with Part 6--After-Repair 
or After-Modification Inspection Program of the Accomplishment 
Instructions of Boeing Service Bulletin 747-53A2396, Revision 1, 
dated February 22, 1996; at the time specified in paragraph (b)(1) 
or (b)(2) of this AD, as applicable.
    (1) For airplanes identified as Groups 1 through 10, inclusive, 
in Boeing Service Bulletin 747-53A2396, Revision 1, dated February 
22, 1996: Inspect within 15,000 flight cycles following 
accomplishment of either paragraph (a)(1) or (a)(2) of this AD.
    (2) For airplanes identified as Group 11 in Boeing Service 
Bulletin 747-53A2396, Revision 1, dated February 22, 1996: Inspect 
prior to the accumulation of 15,000 total flight cycles.
    (c) If no damage is detected during any inspection required by 
paragraph (b) of this AD, repeat the inspections required by 
paragraph (b) of this AD at the following intervals:
    (1) If the immediately preceding inspection was conducted using 
HFEC techniques, conduct the next inspection within 6,000 flight 
cycles.

[[Page 20135]]

    (2) If the immediately preceding inspection was conducted using 
LFEC techniques, conduct the next inspection within 3,000 flight 
cycles.
    (d) If any damage is detected during any inspection required by 
paragraph (b) of this AD, prior to further flight, repair it in 
accordance with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA, Transport Airplane Directorate.
    (e) 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 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (f) 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 April 21, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-10787 Filed 4-24-97; 8:45 am]
BILLING CODE 4910-13-U