[Federal Register Volume 61, Number 221 (Thursday, November 14, 1996)]
[Rules and Regulations]
[Pages 58318-58323]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-28688]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 94-NM-221-AD; Amendment 39-9810; AD 96-23-05]
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 
repetitive inspections to detect cracks and/or corrosion of the girt 
bar support fitting at certain main entry doors (MED); and repair or 
replacement of the support fitting. This amendment also provides for 
various terminating actions for the repetitive inspections. This 
amendment is prompted by reports that, during scheduled deployment 
tests of main entry door slides, corrosion was found on the floor 
structure supports for the escape slides of the main deck entry doors 
on these airplanes. The actions specified by this AD are intended to 
prevent such corrosion, which could result in separation of the escape 
slide from the lower door sill during deployment, and subsequently 
prevent proper operation of the escape slides at the main entry doors 
during an emergency.

DATES: Effective December 16, 1996.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of December 16, 1996.

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: Robert Breneman, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (206) 227-2776; fax (206) 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 February 8, 1995 (60 
FR 7482). That action proposed to require repetitive detailed visual 
inspections to detect cracks and/or corrosion of the girt bar support 
fitting at MED's 1 through 5, inclusive; repair or replacement of the 
support fitting; and reinstallation of the threshold assembly. The 
action also proposed to require, under certain conditions, replacing 
the support fittings with new support fittings having new fasteners; 
refinishing uncorroded support fittings; and removing the corrosion and 
refinishing corroded support fittings. When accomplished, these latter 
actions will constitute terminating action for the repetitive visual 
inspections.
    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

    One commenter supports the proposal.

Request for Clarification of Requirements for Different Configurations 
of Airplanes

    One commenter requests that the proposed rule be revised to clarify 
the actions that are required for variously configured airplanes. The 
FAA has considered each of the commenter's requests, which are iterated 
below:

Doors With Escape Slide/Raft Not Installed or Deactivated

    This commenter requests that the proposal clarify instructions for 
addressing airplanes having doors where an escape slide or slide/raft 
is not installed or is not being used for passenger egress, such as a 
deactivated door 3, at doors 4 and/or 5 of an airplane being operated 
in the ``combi'' configuration, or any door not used for passenger 
egress on a convertible. The commenter suggests that, for these 
airplanes, the proposed requirements of the rule be ``postponed'' until 
such time that any door was reactivated for passenger egress use.
    The FAA concurs with the commenter's suggestion, and has added a 
NOTE in the final rule to indicate this.

Airplanes With Improved Door Fittings Installed

    This commenter requests that the proposal be revised to indicate 
that airplanes on which support fittings have been replaced in 
accordance with Boeing Alert Service Bulletin 747-25A2831, dated August 
29, 1991, require no further action at the replaced fitting locations.
    The FAA concurs. The service bulletin mandated by this AD replaces 
Boeing Alert Service Bulletin 747-25A2831. The FAA has determined that 
the modifications specified in Alert Service Bulletin 747-25A2831 are 
acceptable for compliance with this AD. This AD requires no further 
action on fittings that were replaced or modified in accordance with 
that service bulletin. This final rule has been revised to

[[Page 58319]]

include a new paragraph (m), which clarifies this issue.

Airplanes With Main Entry Door (MED) 1 Fittings

    This commenter states that proposed paragraph (b) should be more 
specific as to the requirements for certain airplanes with Main Entry 
Door 1. As proposed, that paragraph would require that, if no corrosion 
or cracking was found during the initial inspection, operators may 
accomplish either one of two actions:
    1. install a new fitting with new fasteners and reinstall the 
threshold assembly with new corrosion-resistant fasteners; or
    2. reinstall the threshold assembly with new corrosion-resistant 
fasteners and, thereafter, repetitively inspect the girt bar support 
fittings.
    However, this commenter points out that for certain airplanes, line 
numbers 12 through 36, with MED 1 support fittings specified in Figure 
3, Details II, III, or IV, of Boeing Service Bulletin 747-53A2378, the 
instructions in the service bulletin specify that these fittings can 
only be replaced (per item 1, above).
    The FAA acknowledges that the commenter is correct with regard to 
these airplanes, and that the wording of the notice was not clear. By 
referring to Boeing Service Bulletin 747-53A2378, Revision 1, the FAA 
intended that operators follow the appropriate actions specified in it. 
The FAA intended that, based on the configuration of the airplane, 
operators would accomplish the actions that are applicable to their 
airplanes, as defined in the service bulletin. To make this eminently 
clearer, the FAA has revised paragraph (b) of the final rule to clarify 
that operators are to accomplish the action in accordance with the 
``applicable instruction'' in the service bulletin; by doing so, 
operators will be directed to that portion of the service bulletin that 
contains the instructions applicable for their specific airplanes.

Different Configurations of Airplanes Have Different MED Numbers

    This commenter requests that the proposal be revised to clarify the 
fact that:
     Model 747 airplanes that are not ``SP's'' have MED 1, 2, 
3, 4, and 5;
     Model 747SP airplanes have MED 1, 2, 3, and 4.

However, MED 3 and 4 on the Model 747SP correspond in their 
configuration to MED 4 and 5 on the non-SP models. In light of this, 
the commenter requests that the proposed requirements of paragraph (e) 
be clarified to account for these various configurations. Additionally, 
proposed paragraph (i), which relates to MED 3, should be revised to 
indicate that its requirements are applicable only to non-SP airplanes. 
In addition, the commenter points out that the referenced Boeing 
Service Bulletin makes this differentiation in its relevant 
instructions.
    The FAA concurs and has revised paragraphs (e) and (i) of the final 
rule to specify the model and corresponding door number of those 
airplanes subject to the requirements of those paragraphs.

Airplanes With Different Configuration at MED 5

    This commenter states that Boeing Service Bulletin 747-53A2378, 
Revision 1, does not address the configuration of some airplanes at MED 
5 where the support fitting is more like that at MED 1 than at MED 2 
and 4. The commenter states that the service bulletin is being revised 
to contain instructions that will address the access, inspection, 
removal, and replacement of this different type of MED 5 fitting. The 
commenter requests that the proposed rule be revised to contain those 
new instructions.
    The FAA concurs that some additional procedures may be necessary 
for those airplanes. However, at this time, the revised service 
bulletin referred to by the commenter has not been approved and is not 
available. When it is available, the FAA may consider requests for 
approval of the use of it as an alternative method of compliance with 
the requirements of this AD, as provided by paragraph (n).

Request To Make AD Requirements Parallel To Service Bulletin 
Instructions

    One commenter suggests that, if the requirements of the AD are 
identical to the instructions of the Boeing Service Bulletin 747-
53A2378, Revision 1, then the AD should merely state this, instead of 
reiterating each requirement. Another commenter, the airframe 
manufacturer, requests that, if the intent of the proposed AD is to 
mandate the same actions described in that service bulletin, then the 
wording of certain portions of the proposal must be clarified.
    In general, the FAA responds by stating that it did not intend for 
requirements of this AD to deviate significantly from the service 
bulletin instructions. However, certain portions of the AD, such as the 
initial compliance time and other items explained elsewhere in this 
preamble, do differ from the service bulletin. In light of this, a 
statement indicating that the ``AD is identical to the service 
bulletin'' would be incorrect. As for the suggested wording changes 
relative to this issue, each is discussed below:

Actions When Little Corrosion Is Found

    The commenter requests that paragraph (d)(2)(ii) be clarified by 
reordering the required steps to match what is specified in the 
referenced service bulletin. As written, the proposed paragraph could 
be interpreted to mean that operators must first reinstall a repaired 
fitting, and then immediately follow that step by installing a new 
fitting [as specified in proposed paragraph (d)(2)(ii)(A)]. The 
commenter points out that, if the intent of the paragraph is to follow 
the logical sequence of steps as defined in the service bulletin, 
paragraph (d)(2)(ii) should be changed as follows:

    (ii) If blend out of corrosion does not exceed 10 percent of 
original material thickness, accomplish either paragraph 
(d)(2)(ii)(A) or (d)(2)(ii)(B) of this AD:
    (A) Install a new fitting with new fasteners, and reinstall 
threshold assembly with new corrosion-resistant fasteners, in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by paragraph (d) of this 
AD. Or
    (B) Install the repaired fitting with new fasteners and 
reinstall the threshold assembly with corrosion-resistant fasteners, 
in accordance with the service bulletin. Repeat the inspection 
required by paragraph (a) of this AD thereafter at intervals not to 
exceed 6 years.

    The FAA concurs. The intent of the requirements of that paragraph 
was that operators would follow the procedures specified in the 
referenced service bulletin. The FAA finds that the change in wording 
suggested by the commenter suggestion will help to clarify these 
instructions. The final rule has been revised accordingly.

Installing New Fasteners After Primer Application

    The commenter points out that proposed paragraph (f) would require 
removal of the inspected fitting and reinstallation of it with a new 
coat of primer. Likewise, proposed paragraph (j) would require the 
removal of the inspected girt bar support angle, and reinstallation of 
it with a new coat of primer. However, the commenter requests that 
these paragraphs be clarified to state that when, the fitting or angle 
is reinstalled, new fasteners must be used. This is specified in the 
service bulletin, but is not called out precisely in the proposed rule; 
therefore, the commenter considers that operators may be unsure as to 
whether or not new fasteners must be used.
    The FAA concurs that clarification is necessary. As stated 
previously, the intent of this AD is to parallel the

[[Page 58320]]

actions described in the service bulletin. In the particular case of 
proposed paragraphs (f) and (j), the FAA assumed that operators would 
use new fasteners when reinstalling the subject components since that 
action is specified in the instructions laid out in the service 
bulletin, and since those paragraphs state that the required actions 
are to be accomplished ``in accordance with'' that service bulletin. 
However, the FAA acknowledges that this may not be clear to affected 
operators. Therefore, the FAA has revised the two paragraphs to include 
a statement indicating the installation of new fasteners is a necessary 
part of the process of reinstalling the components.

Correct Terminology of Inspection Item

    The commenter requests that proposed paragraph (i) be corrected to 
indicate that the inspection is required to be performed on the ``girt 
bar support angles,'' not the ``girt bar support fitting.'' The follow-
on corrective actions specified in proposed paragraph (j) and (k) 
correctly refer to the ``support angles.''
    The FAA acknowledges this error and has corrected the terminology 
in paragraph (i) accordingly.

Addressing Cracking at Support Angles

    This commenter requests that proposed paragraph (k) be revised to 
clarify that the cracking that is to be addressed is any that is found 
``common to the support angles.'' Additionally, proposed paragraph 
(l)(2)(i), which is a follow-on action to paragraph (k), should be 
revised to specify this same language. The commenter points out that 
this language is used in the referenced Boeing service bulletin and 
likewise should be used in the AD to avoid confusion for operators.
    The FAA concurs, and has revised paragraph (k) and (l)(2)(i) of the 
final rule accordingly.

Inspections of the Support Angles Corner Castings

    The commenter requests that paragraph (k) be clarified to include 
the instructions for addressing cracking that is found in the corner 
casting of the support angles during the inspection required by 
proposed paragraph (i). The commenter points out that special 
instructions are contained in the referenced Boeing service bulletin to 
address this cracking, but these instructions were not specified in the 
proposal. The service bulletin provides for repair of cracks found in 
corner castings, rather than the immediate installation of new angles 
and fasteners if such cracking is found, as would be required by the 
proposal. The commenter maintains that allowing operators to repair 
these cracks rather than replace the components would provide operators 
with time to obtain the replacement corner casting without having to 
ground the airplane. A repaired corner casting would be structurally 
acceptable, since it is not primary load carrying structure.
    The FAA concurs that this repair action should be provided as an 
option to replacement in cases of cracking in the corner casting. 
However, the service bulletin does not sufficiently describe all of the 
actions that are necessary to repair the part. The FAA considers that 
cracked corner castings should be addressed on a case-by-case basis. 
Therefore, operators that prefer to repair a cracked corner casting, as 
an option to replacing it, should request an alternative method of 
compliance with this portion of the AD, as provided by paragraph (n). 
Paragraph (k)(2) of this final rule has been revised accordingly.

Requests To Extend the Compliance Time

    Several commenters request that the proposal be revised to require 
operators to perform the initial visual inspections prior to an 
airplane accumulating 16 years of service or 18 months--rather than the 
proposed 15 months--after the effective date of the final rule, 
whichever is later:
    1. One of these commenters states that the Corrosion Prevention and 
Control Program, which was mandated by AD 90-25-05 [amendment 39-6790, 
(55 FR 31401, November 27, 1990)], already requires inspections in this 
area at 18-month intervals. Allowing the proposed inspections to be 
accomplished at this same interval would reduce the economic burden on 
affected operators, since they would not have to special schedule 
airplanes for those inspections.
    2. Another commenter states that some of the proposed inspections 
will necessarily require that the galley be removed from the airplanes. 
This removal activity is so extensive that it is normally accomplished 
at main base locations when airplanes are undergoing their regularly 
scheduled 18-month ``C'' check activity. By extending the proposed 
compliance time to correspond with this activity, operators would not 
be required to schedule special times for the accomplishment of this 
inspection, at considerable additional expense. Additionally, it will 
allow the inspections and any necessary installation or repair to be 
performed at a main maintenance base where special equipment and 
trained maintenance personnel will be available, if necessary.
    3. Finally, another commenter points out that the lead time for 
obtaining some of the parts that may be necessitated by the proposed 
actions may take as long as 37 months; the proposed 15-month compliance 
time would make it very difficult to place a parts order in time to 
comply with the AD.
    The FAA concurs that the compliance time may be extended to 18 
months. In consideration of all of the factors raised by the 
commenters, as well as the demonstrated reliability and safety features 
of the Model 747, and the likelihood of having to perform an emergency 
evacuation during the compliance period, the FAA finds that extending 
the compliance time by a modest 3 additional months will have an 
insignificant effect on safety, while significantly reducing the burden 
on the affected operators.

Request To Shorten the Compliance Time

    One commenter supports the proposal, but requests that it be 
revised to require operators to perform the initial visual inspections 
prior to an airplane accumulating 16 years of service or 6 months--
rather than the proposed 15 months--after the effective date of the 
final rule, whichever is later. The commenter provided no technical 
justification for this request, but indicated that it was based on its 
general feeling that the proposed AD is vital to the safety and well-
being of the traveling public. This commenter considers the problem 
addressed to be an extremely hazardous situation that could endanger 
the lives of both passengers and cabin crew.
    The FAA does not concur with this commenter's request. While the 
FAA does not intend in any way to depreciate the commenter's statements 
relative to the unsafe condition, as discussed previously, the FAA is 
obligated to weigh many other factors in addition to safety when 
developing an appropriate compliance time. In the case of this AD, the 
FAA considered not only the safety implications, but normal maintenance 
schedules for timely accomplishment of the actions, parts availability, 
recommendations of the airframe manufacturer based on crack analysis 
and service reports, the reliability of the affected fleet, and the 
probability of an incident occurring that is associated with the 
problem addressed by the AD. In light of all of these factors, the FAA 
has determined that a reduction of the compliance time is not 
warranted.

[[Page 58321]]

Request To Clarify Replacement Requirements

    One commenter requests that the proposal be revised to clarify that 
the replacement of fittings or fasteners is required only if cracking 
or corrosion is found. The commenter states that, as the proposal is 
written, if an inspection shows that no cracking or corrosion is 
present, an operator may accomplish one of two possible actions:
    1. install a new fitting with new fasteners in the cracking 
location; or
    2. reinstall corrosion-resistant fasteners in the threshold 
assembly and repeat the inspection thereafter every 6 years.
    The commenter states that one could conclude from the wording of 
this second option that the operators would have to install corrosion-
resistant fasteners every six years, regardless of whether or not 
corrosion was present. If this is not the FAA's intent, the commenter 
requests that this requirement be clarified.
    The FAA concurs that clarification is necessary. It is not the 
FAA's intent that fasteners be replaced at every inspection, regardless 
of whether corrosion is present or not. The only time that the 
replacement must be accomplished is if corrosion is detected during the 
inspection. The FAA has added wording to the appropriate portions of 
the final rule to clarify this requirement.

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 previously 
described. The FAA has determined that these changes will not increase 
the economic burden on any operator. Additionally, these changes do not 
increase the scope of the AD, and are a logical outgrowth of the notice 
that does not necessitate providing an additional opportunity for 
public comment.

Cost Impact

    There are approximately 868 Boeing Model 747 series airplanes of 
the affected design in the worldwide fleet. The FAA estimates that 169 
airplanes of U.S. registry will be affected by this AD.
    The inspection of MED 1 will take approximately 81 work hours per 
door to accomplish, at an average labor rate of $60 per work hour. 
Based on these figures, the cost impact of this required inspection on 
U.S. operators is estimated to be $4,860 per door.
    The inspection of MED's 2, 4, and 5 (MED 2, 3, and 4 on Model 747 
SP series airplanes) will take approximately 7 work hours per door to 
accomplish, at an average labor rate of $60 per work hour. Based on 
these figures, the cost impact of this required inspection on U.S. 
operators is estimated to be $420 per door.
    The inspection of MED 3 would take approximately 13 work hours per 
door to accomplish, at an average labor rate of $60 per work hour. 
Based on these figures, the cost impact of this required inspection on 
U.S. operators is estimated to be $780 per door.
    The replacement of both support fittings will take approximately 37 
work hours per door to accomplish, at an average labor rate of $60 per 
work hour. Based on these figures the cost impact of the required 
replacement on U.S. operators is estimated to be $2,200 per door.
    The cost impact figures 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 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:

96-23-05  Boeing: Amendment 39-9810. Docket 94-NM-221-AD.

    Applicability: Model 747 series airplanes; line numbers 1 
through 868 inclusive, excluding freighters and special freighters; 
certificated in any category.

    Note 1: The requirements of this AD are not applicable to doors 
where an escape slide or slide/raft is not installed or is not used 
for passenger egress (such as a deactivated door 3, at doors 4 and/
or 5 of an airplane being operated in the ``combi'' configuration, 
or any door not used for passenger egress on a convertible). The 
requirements of this rule become applicable at the time when an 
escape slide or slide/raft is installed on such doors, or when such 
doors are activated and/or converted for passenger use. The 
requirements also become applicable at the time an airplane 
operating in an all-cargo configuration is converted to a passenger 
or passenger/cargo configuration.
    Note 2: 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 (n) 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 corrosion on girt bar support fittings, 
which could result in separation of the escape slide from the lower 
door sill during deployment, and subsequently prevent operation of 
the escape slides at the main entry doors during an emergency, 
accomplish the following:
    (a) For airplanes equipped with Main Entry Door (MED) 1: Prior 
to the accumulation of 16 years of service since date of manufacture 
of the airplane, or within 18 months after the effective date of 
this AD, whichever occurs later, perform a detailed visual 
inspection to detect cracking and/or corrosion of the girt bar 
support fitting at the left and right MED 1, in accordance with 
Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 
1994.
    (b) If no cracking or corrosion is found during the inspection 
required by paragraph

[[Page 58322]]

(a) of this AD, prior to further flight, accomplish either paragraph 
(b)(1) or (b)(2) of this AD, in accordance with the applicable 
instructions specified in Boeing Service Bulletin 747-53A2378, 
Revision 1, dated March 10, 1994.
    (1) Install a new fitting with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners, in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by paragraph (b) of this 
AD. Or
    (2) Reinstall the threshold assembly with corrosion-resistant 
fasteners, in accordance with the service bulletin. Thereafter, 
repeat the inspection required by paragraph (a) of this AD at 
intervals not to exceed 6 years.
    (c) If any cracking is found during the inspection required by 
paragraph (a) or (b)(2) of this AD, prior to further flight, install 
a new fitting with new fasteners, and reinstall the threshold 
assembly with new corrosion-resistant fasteners, in accordance with 
Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 
1994. After these actions are accomplished, no further action is 
required by this paragraph.
    (d) If any corrosion is found during the inspection required by 
paragraph (a) or (b)(2) of this AD, prior to further flight, 
accomplish either paragraph (d)(1) or (d)(2) of this AD, in 
accordance with Boeing Service Bulletin 747-53A2378, Revision 1, 
dated March 10, 1994.
    (1) Install a new fitting with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by this paragraph. Or
    (2) Blend out corrosion in accordance with the service bulletin.
    (i) If blend out of corrosion is beyond 10 percent of original 
thickness or any crack is found during accomplishment of the blend 
out procedures, install a new fitting with new fasteners, and 
reinstall the threshold assembly with new corrosion-resistant 
fasteners, in accordance with the service bulletin. After these 
actions are accomplished, no further action is required by this 
paragraph.
    (ii) If blend out of corrosion does not exceed 10 percent of 
original material thickness, accomplish either paragraph 
(d)(2)(ii)(A) or (d)(2)(ii)(B) of this AD:
    (A) Install a new fitting with new fasteners, and reinstall 
threshold assembly with new corrosion-resistant fasteners, in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by this paragraph. Or
    (B) Install the repaired fitting with new fasteners and 
reinstall the threshold assembly with corrosion-resistant fasteners, 
in accordance with the service bulletin. Thereafter, repeat the 
inspection, and corrective actions as necessary, required by 
paragraph (a) of this AD at intervals not to exceed 6 years.
    (e) For airplanes equipped with Main Entry Doors (MED) 2, 4, 
and/or 5 (MED 2, 3, and/or 4 on Model 747SP series airplanes): Prior 
to the accumulation of 10 years of service since date of manufacture 
of the airplane, or within 18 months after the effective date of 
this AD, whichever occurs later, perform a detailed visual 
inspection to detect cracking and/or corrosion of the girt bar 
support fitting at the left and right MED 2, 4, and 5 (MED 2, 3, and 
4 on Model 747SP series airplanes), in accordance with Boeing 
Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994.
    (f) If no cracking or corrosion is found during the inspection 
required by paragraph (e) of this AD, prior to further flight, 
accomplish either paragraph (f)(1) or (f)(2) of this AD, in 
accordance with the applicable instructions in Boeing Service 
Bulletin 747-53A2378, Revision 1, dated March 10, 1994.
    (1) Remove the inspected fitting and reinstall it with a new 
coat of primer and new fasteners; and reinstall the threshold 
assembly with new corrosion-resistant fasteners; in accordance with 
the service bulletin. After these actions are accomplished, no 
further action is required by this paragraph. Or
    (2) Reinstall the serrated plate assembly and the girt bar floor 
fitting with corrosion-resistant fasteners, in accordance with the 
service bulletin. Thereafter, repeat the inspection required by 
paragraph (e) of this AD at intervals not to exceed 6 years.
    (g) If any cracking is found during the inspection required by 
paragraph (e) or (f)(2) of this AD, prior to further flight, install 
a new fitting with new fasteners, and reinstall the threshold 
assembly with new corrosion-resistant fasteners, in accordance with 
Boeing Service Bulletin 747-53A2378, Revision 1, dated March 10, 
1994. After these actions are accomplished, no further action is 
required by this paragraph.
    (h) If any corrosion is found during the inspection required by 
paragraph (e) or (f)(2) of this AD, prior to further flight, 
accomplish either paragraph (h)(1) or (h)(2) of this AD, in 
accordance with Boeing Service Bulletin 747-53A2378, Revision 1, 
dated March 10, 1994.
    (1) Install a new fitting with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners, in 
accordance with the service bulletin. After these actions are 
accomplished, no further action is required by this paragraph. Or
    (2) Blend out corrosion in accordance with the service bulletin.
    (i) If blend out of corrosion is beyond 10 percent of original 
thickness or any crack is found during accomplishment of the blend 
out procedures, install a new fitting with new fasteners, and 
reinstall the threshold assembly with new corrosion-resistant 
fasteners, in accordance with the service bulletin. After these 
actions are accomplished, no further action is required by this 
paragraph.
    (ii) If blend out of corrosion does not exceed 10 percent of 
original material thickness, install the repaired fitting with new 
fasteners, and reinstall the threshold assembly with new corrosion-
resistant fasteners, in accordance with the service bulletin. After 
these actions are accomplished, no further action is required by 
this paragraph.
    (i) For airplanes equipped with Main Entry Door (MED) 3 (this 
paragraph does not apply to Model 747SP series airplanes): Prior to 
the accumulation of 16 years of service since date of manufacture of 
the airplane, or within 18 months after the effective date of this 
AD, whichever occurs later, perform a detailed visual inspection to 
detect cracking and/or corrosion of the girt bar support angles at 
the left and right MED 3, in accordance with Boeing Service Bulletin 
747-53A2378, Revision 1, dated March 10, 1994.
    (j) If no cracking or corrosion is found during the inspection 
required by paragraph (i) of this AD, prior to further flight, 
accomplish either paragraph (j)(1) or (j)(2) of this AD in 
accordance with the applicable instructions in Boeing Service 
Bulletin 747-53A2378, Revision 1, dated March 10, 1994.
    (1) Remove inspected angle and reinstall it with a new coat of 
primer and new fasteners; and reinstall the threshold assembly with 
new corrosion-resistant fasteners, in accordance with the service 
bulletin. After these actions are accomplished, no further action is 
required by this paragraph. Or
    (2) Reinstall the corner scuff plate and the threshold apron 
with corrosion-resistant fasteners, in accordance with the service 
bulletin. Thereafter, repeat the inspection required by paragraph 
(i) of this AD at intervals not to exceed 6 years.
    (k) If any crack common to the support angles is found during 
the inspection required by paragraph (i) or (j)(2) of this AD, prior 
to further flight, accomplish the actions specified in paragraph 
(k)(1) or (k)(2), as applicable, in accordance with Boeing Service 
Bulletin 747-53A2378, Revision 1, dated March 10, 1994:
    (1) Install the new angles with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners. After 
these actions are accomplished, no further action is required by 
this paragraph of this AD.
    (2) For any cracking found only in the corner casting as 
specified in the service bulletin, accomplish either paragraph 
(k)(2)(i) or (k)(2)(ii) prior to further flight:
    (i) Replace the corner casting in accordance with the service 
bulletin. Or
    (ii) Repair the cracked part in accordance with a method 
approved by the Manager, Seattle Aircraft Certification Office 
(ACO), FAA, Transport Airplane Directorate. Refer to paragraph (n) 
of this AD for the appropriate procedure for seeking such an 
approval. (This option is provided in order to give operators time 
to obtain a replacement corner casing without grounding an 
airplane.) This repair is considered temporary action only; 
replacement of the corner casting eventually must be accomplished in 
accordance with a schedule prescribed by the Manager, Seattle ACO.
    (l) If any corrosion is found during the inspection required by 
paragraph (i) of this AD, prior to further flight, accomplish either 
paragraph (l)(1) or (l)(2) of this AD, in accordance with Boeing 
Service Bulletin 747-53A2378, Revision 1, dated March 10, 1994.
    (1) Install the new angles with new fasteners, and reinstall the 
threshold assembly with new corrosion-resistant fasteners, in 
accordance with the service bulletin. After these actions are

[[Page 58323]]

accomplished, no further action is required by this paragraph. Or
    (2) Blend out corrosion in accordance with the service bulletin.
    (i) If blend out of corrosion is beyond 10 percent of original 
thickness, or if any crack common to the support angles is found 
during accomplishment of the blend out procedures, install the new 
angles with new fasteners, and reinstall the threshold assembly with 
new corrosion-resistant fasteners, in accordance with the service 
bulletin. After these actions are accomplished, no further action is 
required by this paragraph.
    (ii) If blend out of corrosion does not exceed 10 percent of 
original material thickness, install the repaired angles with new 
fasteners, and reinstall the threshold assembly with new corrosion-
resistant fasteners, in accordance with the service bulletin. After 
these actions are accomplished, no further action is required by 
this paragraph.
    (m) Installation of a girt bar support fitting in accordance 
with Boeing Service Bulletin 747-25A2831, dated August 29, 1991, is 
considered acceptable for compliance with the requirements of this 
AD for each affected fitting location.
    (n) 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 request through an appropriate FAA Principal 
Maintenance Inspector, who may add comments and then send it to the 
Manager, Seattle ACO.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (o) 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.
    (p) The actions shall be done in accordance with Boeing Service 
Bulletin 747-53A2378, Revision 1, dated March 10, 1994. 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.
    (q) This amendment becomes effective on December 16, 1996.

    Issued in Renton, Washington, on October 31, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-28688 Filed 11-13-96; 8:45 am]
BILLING CODE 4910-13-U