[Federal Register Volume 59, Number 43 (Friday, March 4, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-4954]


[[Page Unknown]]

[Federal Register: March 4, 1994]


-----------------------------------------------------------------------


DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 93-NM-212-AD]

 

Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

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 inspection to detect cracking of 
certain fuselage longitudinal lap joints, repair of any cracking found, 
and replacement of the countersunk fasteners in those laps joints with 
protruding head fasteners. This proposal is prompted by a structural 
reassessment of Model 747 series airplanes. The actions specified by 
the proposed AD are intended to prevent skin cracking in the 
longitudinal lap joints of certain stringers, which can lead to rapid 
decompression of the airplane.

DATES: Comments must be received by April 29, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 93-NM-212-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-212-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-212-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    Recently, the Boeing Commercial Airplane Group, manufacturer of 
Model 747 series airplanes, conducted a structural reassessment of 
these airplanes. The FAA has reviewed the results of this reassessment 
and has determined that the longitudinal lap joints of Stringer (S-)12 
are critical to the structural integrity of these airplanes. -
    The upper skin in the S-12 longitudinal lap joints are made of 
waffle doublers that are hot bonded to skin panels. The S-12 
longitudinal lap joints have three rows of countersunk fasteners. The 
depth of the countersink exceeds the thickness of the skin panel. If 
the waffle doubler disbonds from the skin panel, the resultant sharp 
edges at the longitudinal lap joint fasteners can cause fatigue 
cracking at the fastener holes.
    Skin cracking in the longitudinal lap joints of S-12L and S-12R, if 
not detected and corrected, could result in rapid decompression of the 
airplane.
    The FAA has reviewed and approved Boeing Service Bulletin 747-53-
2366, dated August 6, 1992, that describes procedures for repetitive 
high frequency eddy current (HFEC) inspections to detect cracking of 
the skin around the fasteners in the upper row of the longitudinal lap 
joints of S-12L and S-12R from station 520 to station 741.1, and 
replacement of the countersunk fasteners in these longitudinal lap 
joints with protruding head fasteners.
    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 repetitive external HFEC inspections to 
detect cracking of the skin around the fasteners in the upper row of 
the longitudinal lap joints of S-12L and S-12R from station 520 to 
station 741.1, and replacement of the countersunk fasteners in these 
longitudinal lap joints with protruding head fasteners. The actions 
would be required to be accomplished in accordance with the service 
bulletin described previously. This proposal also would require repair 
of all cracking in accordance with procedures specified in the 747 
Structural Repair Manual.
    This proposal is applicable only to airplanes having line numbers 
201 through 230. Since the tolerance specifications for the bonding 
process for airplanes manufactered after line number 230 were more 
stringent, those airplanes are not subject to the unsafe condition 
addressed by this proposed AD.
    There are approximately 30 Model 747 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 12 
airplanes of U.S. registry would be affected by this proposed AD, that 
it would take approximately 17 work hours per airplane to accomplish 
the proposed inspections, and that the average labor rate is $55 per 
work hour. Based on these figures, the total cost impact of the 
proposed inspections on U.S. operators is estimated to be $11,220, or 
$935 per airplane.
    The FAA estimates that it would take approximately 302 work hours 
per airplane to accomplish the proposed requirement to replace 
fasteners, and that the average labor rate is $55 per work hour. 
Required parts would be nominal in cost. Based on these figures, the 
total cost impact of the proposed requirement to replace fasteners on 
U.S. operators is estimated to be $199,320, or $16,610 per airplane.
    Based on the figures, above, the total cost impact of the proposed 
actions (cost of inspections added to the cost of replacement of 
fasteners) on U.S. operators is estimated to be $210,540, or $17,545 
per airplane.
    The FAA recognizes that the proposed replacement of fasteners would 
require a large number of work hours to accomplish. However, the 4-year 
compliance time specified in paragraph (b) of this proposed AD should 
allow ample time for the replacement of the fasteners to be 
accomplished coincidentally with scheduled major airplane inspection 
and maintenance activities, thereby minimizing the costs associated 
with special airplane scheduling. -
    The total cost impact figure discussed above is 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.
    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 adding the following new 
airworthiness directive:

Boeing: Docket 93-NM-212-AD.
    Applicability: Model 747 series airplanes, having line numbers 
201 through 230 inclusive; certificated in any category. -
    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent rapid decompression of the airplane, accomplish the 
following:
    (a) Prior to the accumulation of 15,000 total flight cycles or 
within 1,000 flight cycles after the effective date of this AD, 
whichever occurs later, perform an external high frequency eddy 
current (HFEC) inspection to detect cracking of the skin at the 
upper row of countersunk fasteners in the longitudinal lap joints of 
Stringer (S-)12L and S-12R from station 520 to station 741.1, in 
accordance with Boeing Service Bulletin 747-53-2366, dated August 6, 
1992.
    (1) If no cracking is found, repeat the inspection thereafter at 
intervals not to exceed 4,000 flight cycles until the replacement of 
fasteners required by paragraph (b) of this AD is accomplished.
    (2) If any cracking is found, prior to further flight, repair in 
accordance with the 747 Structural Repair Manual. After repair, 
repeat the inspection at intervals not to exceed 4,000 flight cycles 
until the replacement of fasteners required by paragraph (b) of this 
AD is accomplished.
    (b) Prior to the accumulation of 20,000 total flight cycles or 
within 4 years after the effective date of this AD, whichever occurs 
later, replace the countersunk fasteners in the upper row of the 
longitudinal lap joints of S-12L and S-12R from station 520 to 
station 741.1 with protruding head fasteners in accordance with 
Boeing Service Bulletin 747-53-2366, dated August 6, 1992. 
Replacement of these fasteners constitutes terminating action for 
the repetitive inspections required by paragraph (a) of this AD.
    (c) Prior to the accumulation of 10,000 total flight cycles 
after replacement of the countersunk fasteners required by paragraph 
(b) of this AD, perform an external HFEC inspection to detect 
cracking of the skin at the upper row of protruding head fasteners 
in the longitudinal lap joints of S-12L and S-12R from station 520 
to station 741.1 in accordance with Boeing Service Bulletin 747-53-
2366, dated August 6, 1992.
    (1) If no cracking is found, repeat the inspection thereafter at 
intervals not to exceed 3,000 flight cycles.
    (2) If any cracking is found, prior to further flight, repair in 
accordance with the 747 Structural Repair Manual. After repair, 
repeat the inspection at intervals not to exceed 3,000 flight 
cycles.
    (d) 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.

    (e) Special flight permits may be issued in accordance with 
Federal Aviation Regulations (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 February 28, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-4954 Filed 3-3-94; 8:45 am]
BILLING CODE 4910-13-U