[Federal Register Volume 63, Number 244 (Monday, December 21, 1998)]
[Rules and Regulations]
[Pages 70316-70319]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-33541]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-59-AD; Amendment 39-10954; AD 98-26-13]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 747 series airplanes, that requires 
a one-time inspection to determine the material type of the stop 
support fittings of the main entry doors. This AD also requires 
repetitive visual inspections to detect cracks of certain stop support 
fittings of the main entry doors, and replacement of any cracked stop 
support fitting with a certain new stop support fitting. This amendment 
is prompted by reports that stress corrosion cracking was found on 
certain stop support fittings of the main entry doors. The actions 
specified by this AD are intended to detect and correct such stress 
corrosion cracking, which could lead to failure of the stop support 
fittings. Failure of the stop support fittings could result in loss of 
a main entry door and consequent rapid decompression of the airplane.

DATES: Effective January 25, 1999.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of January 25, 1999.

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: Bob Breneman, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2776; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to certain Boeing Model 747 series 
airplanes was published in the Federal Register on March 20, 1998 (63 
FR 13566). That action proposed to require a one-time

[[Page 70317]]

inspection to determine the material type of the stop support fittings 
of the main entry doors. That action also proposed to require 
repetitive visual inspections to detect cracks of certain stop support 
fittings of the main entry doors, and replacement of any cracked stop 
support fitting with a certain new stop support fitting.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

Support for the Proposal

    Several commenters support the proposed rule.

Request to Include a Threshold for Initial Inspection

    Two commenters request that the proposed compliance time for the 
initial high frequency eddy current (HFEC) inspection to determine the 
material type of the stop support fittings of the main entry doors be 
revised from 18 months after the effective date of this AD, as stated 
in the proposal, to 6 years after delivery of the airplane or 18 months 
after the effective date of the AD, whichever occurs later. One of the 
commenters points out that cracking of the fittings has been attributed 
to stress corrosion and that, when corrosion prevention is performed 
properly [i.e., in accordance with the Corrosion Prevention and Control 
Program (CPCP)], the growth of corrosion cracking is very slow. The 
commenter notes that corrosion and stress corrosion cracking is 
unlikely to occur on younger airplanes.
    The FAA does not concur with the commenters' request to include a 
threshold for the initial inspection. As stated previously in the 
notice of proposed rulemaking (NPRM), the FAA has determined that all 
affected airplanes are older than 6 years since the date of manufacture 
of the airplane. The youngest airplane has been in service for more 
than seven years. Therefore, all operators are required to perform the 
initial inspection of the affected airplanes within 18 months after the 
effective date of this AD. No change to the final rule is necessary in 
this regard.

Request to Limit the Area of Inspection

    One commenter requests that the proposed HFEC inspection to 
determine the material type of the stop support fittings of the main 
entry doors should be required only if the material of the stop support 
fittings is unknown, as specified in Figure 3, Table 1, of the 
referenced service bulletin.
    The FAA concurs with the commenter that the HFEC inspection 
required by this AD should be required only for those stop support 
fittings. The FAA's intent is that the HFEC inspection be accomplished 
only at the locations specified in the referenced service bulletin, 
where the material type is unknown. The visual inspection must be 
accomplished only on those stop support fittings of the main entry 
doors that are made from either 7079-T651 or 7075-T651 material. The 
FAA has revised paragraph (a) of the final rule to clarify this point.

Request to Extend Repetitive Inspection Intervals

    Several commenters request that the repetitive interval for 
accomplishment of the visual inspections to detect cracks of certain 
stop support fittings of the main entry doors be extended from the 
proposed 18 months to 36 months, as specified in Boeing Service 
Bulletin 747-53-2358, dated August 26, 1993 (which was referenced as 
the appropriate source of service information in the NPRM). One of the 
commenters notes that the cracks on the affected stop support fittings 
are attributed to stress corrosion, which is a function of environment 
and time. As such, the inspection interval specified in the service 
bulletin is based on results of inspections of the fleet of Model 747 
series airplanes, and on the degree of corrosion or cracking found 
during those inspections. Another commenter notes that the growth rate 
of stress corrosion cracks depends mainly on the environment and the 
age of the airplane, and that growth of such cracks is relatively slow 
when corrosion prevention measures are accomplished properly in 
accordance with the CPCP.
    One of these commenters also requests that the repetitive interval 
for the visual inspections be extended from the proposed 18 months to 
2,000 flight cycles or 36 months, whichever occurs first. That 
commenter points out that the 18-month intervals specified in the 
proposal are not consistent with the inspection intervals of 2,000 
flight cycles that are specified for inspections of similar fittings at 
main entry door 5 that are required by AD 92-02-01, amendment 39-8137 
(57 FR 5373, February 14, 1992).
    The FAA concurs with the commenters' requests to extend the 
repetitive visual inspection intervals. As a result of these comments, 
the FAA has reviewed results from inspections of similar fittings of 
main entry door 5 that were accomplished in accordance with AD 92-02-
01. Based on this review, the FAA has determined that repetitive 
inspections of fittings that are accomplished at 2,000-flight-cycle 
intervals are sufficient to detect cracked fittings in a timely manner. 
Therefore, the FAA has revised paragraph (a)(2)(i) of the final rule to 
state, ``. . . repeat the visual inspection thereafter at intervals not 
to exceed 36 months or 2,000 flight cycles, whichever occurs first.''

Request to Allow Continued Use of Subject Stop Support Fittings

    One commenter requests that the proposal be revised to allow 
cracked stop support fittings of the main entry doors to be replaced 
with new stop support fittings that are made from either 7079-T651 or 
7075-T651 material, provided that repetitive inspections of the 
replacement parts are performed at intervals of 36 months. The 
commenter states that a non-cracked stop support fitting made from 
7079-T651 or 7075-T651 material provides the required strength 
capability. The commenter also notes that discarding all spares of stop 
support fittings made from 7079-T651 or 7075-T651 material is a waste 
of resources.
    The FAA infers that the commenter is requesting that paragraph 
(a)(2)(ii) of the proposal be revised to allow installation of new 
parts made from either 7079-T651 or 7075-T651 material, or parts made 
from 7075-T73 material, and that paragraph (c) of the proposal not be 
included in the final rule. The FAA does not concur with the 
commenter's request to allow continued use of the subject stop support 
fittings. The FAA has determined that the cracking of the stop support 
fittings of the main entry doors is caused by a combination of internal 
residual stress resulting from the manufacturing process, clamp-up 
stress from the installation of the fittings, operational stress due to 
pressurization of the airplane, and stress corrosion. Other parts made 
from 7079-T651 or 7075-T651 material previously have been found to 
crack while in storage, due to internal residual stress. While the FAA 
is not requiring the replacement of uncracked stop support fittings of 
the main entry doors, the FAA will not promote long-term inspections of 
the stop support fittings by approving the installation of replacement 
parts that are subject to the same unsafe condition. No change to the 
final rule is necessary in this regard.

Request to Amend Aging Fleet Inspection and Modification Program

    One commenter suggests that Boeing Service Bulletin 747-53-2358 be 
reviewed by the 747 Structures Task Group (STG) for possible inclusion 
in

[[Page 70318]]

the aging aircraft inspection or modification program.
    The FAA infers that the commenter is requesting that the FAA delay 
issuance of the final rule until the STG has reviewed Boeing Service 
Bulletin 747-53-2358 and considered including that service bulletin in 
Boeing Document No. D6-35999, dated March 1989, ``Aging Airplane 
Service Bulletin Structural Modification Program, Model 747.'' [The FAA 
previously issued AD 90-06-06, amendment 39-6490 (55 FR 8374, March 7, 
1990), which requires incorporation of certain structural modifications 
in accordance with Boeing Document No. D6-35999.]
    The FAA does not concur. The FAA has determined that rulemaking is 
necessary to address the unsafe condition (stress corrosion cracking on 
certain stop support fittings of the main entry doors, which could 
result in failure of the stop support fittings, loss of a main entry 
door, and consequent rapid decompression of the airplane). By issuing 
this new rule, the FAA has taken action to ensure that the stop support 
fittings of the main entry doors on the affected Boeing Model 747 
series airplanes are inspected and replaced, if necessary, in a timely 
manner. This action does not preclude a review of Boeing Service 
Bulletin 747-53-2358 by the STG for possible inclusion in Boeing 
Document No. D6-35999. However, the FAA finds that to delay this action 
would be inappropriate in light of the identified unsafe condition. 
Therefore, no change to the final rule is necessary in this regard.

Explanation of Additional Changes Made to This Final Rule

    In the proposal, paragraph (a)(1) reads, ``If the fitting is made 
from 7075-T73 material, no further action is required by this AD.'' 
Since the issuance of the NPRM, the FAA has determined that such 
language could be misleading to operators, because follow-on actions 
are required for any stop support fitting of the main entry door that 
is made from 7079-T651 or 7075-T651 material, regardless of whether 
other stop support fittings are made from 7075-T73 material. Therefore, 
paragraph (a)(1) of the final rule has been revised to read, ``. . . no 
further action is required by this AD for that fitting.''

Conclusion

    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 changes described 
previously. The FAA has determined that these changes will neither 
increase the economic burden on any operator nor increase the scope of 
the AD.

Cost Impact

    There are approximately 515 Boeing Model 747 series airplanes of 
the affected design in the worldwide fleet. The FAA estimates that 164 
airplanes of U.S. registry will be affected by this AD.
    It will take approximately 1 work hour per door to accomplish the 
required HFEC inspection, at an average labor rate of $60 per work 
hour. Based on these figures, the cost impact of the HFEC inspection 
required by this AD on U.S. operators is estimated to be $60 per door.
    The 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.
    Should an operator be required to accomplish the required visual 
inspection, it will take approximately 2 work hours per door to 
accomplish the required actions, at an average labor rate of $60 per 
work hour. Based on these figures, the cost impact of the visual 
inspection required by this AD on U.S. operators is estimated to be 
$120 per door.
    Should an operator elect to accomplish the optional terminating 
action that is provided by this AD action, the number of hours required 
to accomplish it would be approximately 124 work hours per door, at an 
average labor rate of $60 per work hour. Required parts would cost 
approximately $13,000 per door. Based on these figures, the cost impact 
of the optional terminating action on U.S. operators is estimated to be 
$20,440 per door.

Regulatory Impact

    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. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

98-26-13  BOEING: Amendment 39-10954. Docket 97-NM-59-AD.

    Applicability: Model 747-100, -100B, -200, -200B, -200C, -300, -
400, and 747SR series airplanes; having line numbers 1 through 830 
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 (d) 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 stress corrosion cracking of the stop 
support fittings of the main entry doors and the resultant failure 
of the stop support fittings, which could result in loss of a main 
entry door and consequent rapid decompression of the airplane, 
accomplish the following:
    (a) Within 18 months after the effective date of this AD, 
perform a high frequency eddy current inspection to determine the 
material type of the stop support fittings of

[[Page 70319]]

the main entry doors, in accordance with the Accomplishment 
Instructions of Boeing Service Bulletin 747-53-2358, dated August 
26, 1993. Perform the inspection only at those locations where the 
material type of the stop support fittings is unknown, as specified 
in Figure 3, Table 1, of the service bulletin.
    (1) If the fitting is made from 7075-T73 material, no further 
action is required by this AD for that fitting.
    (2) If the fitting is NOT made from 7075-T73 material, prior to 
further flight, perform a visual inspection to detect cracks of the 
stop support fitting of the main entry doors, in accordance with the 
service bulletin.
    (i) If no crack is detected, repeat the visual inspection 
thereafter at intervals not to exceed 36 months or 2,000 flight 
cycles, whichever occurs first.
    (ii) If any crack is detected, prior to further flight, replace 
the fitting with a stop support fitting made from 7075-T73 material, 
in accordance with the service bulletin.
    (b) Replacement of the stop support fitting of the main entry 
doors with a stop support fitting made from 7075-T73 material, in 
accordance with Boeing Service Bulletin 747-53-2358, dated August 
26, 1993, constitutes terminating action for the repetitive 
inspection requirements of this AD for the replaced fitting.
    (c) As of the effective date of this AD, no person shall install 
a stop support fitting made from either 7079-T651 or 7075-T651 
material on any airplane.
    (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 2: 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 
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.
    (f) The actions shall be done in accordance with Boeing Service 
Bulletin 747-53-2358, dated August 26, 1993. 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.
    (g) This amendment becomes effective on January 25, 1999.

    Issued in Renton, Washington, on December 14, 1998.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-33541 Filed 12-18-98; 8:45 am]
BILLING CODE 4910-13-U