[Federal Register Volume 63, Number 142 (Friday, July 24, 1998)]
[Proposed Rules]
[Pages 39765-39769]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-19460]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-163-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 all Boeing Model 747 series 
airplanes. This proposal would require a one-time inspection to detect 
discrepancies of the center fuel tank, and corrective actions, if 
necessary; replacement of all components of the fuel quantity 
indicating system (FQIS) of the center tanks with new FQIS components; 
and replacement of the FQIS wiring with new wiring. For certain 
airplanes, this proposal also would require a one-time inspection to 
detect discrepancies of the FQIS, and corrective actions, if necessary; 
and installation of a flame arrestor in the scavenge pumps of the 
center fuel tank. This proposal is prompted by design review and 
testing results obtained in support of an accident investigation. The 
actions specified by the proposed AD are intended to prevent ignition 
sources and consequent fire/explosion in the center fuel tank.

DATES: Comments must be received by September 8, 1998.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-163-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.
    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: Dionne Stanley, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2250; fax (425) 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 98-NM-163-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-114, Attention: Rules 
Docket No. 98-NM-163-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On July 17, 1996, a Boeing Model 747 series airplane was involved 
in an accident shortly after takeoff from John F. Kennedy International 
Airport in Jamaica, New York. In support of the subsequent accident 
investigation, the FAA has participated in design review and testing to 
determine possible sources of ignition in the center fuel tank. The 
cause of the accident has not yet been determined.
    This design review has identified the need to detect any conditions 
of in-service deterioration of the wiring, bonding, tubing 
installations, and other component installations inside the center fuel 
tank. If such conditions are detected, repair of these discrepancies 
would reduce the likelihood of these components becoming in-tank 
ignition sources due to lightning strikes, static electricity, or 
electrical failures outside of the fuel tank.
    In addition, investigation has revealed that the knurled terminal 
blocks on ``series 3'' (and earlier series) probes of the fuel quantity 
indication system (FQIS) on Model 747 series airplanes are subject to 
chafing against their

[[Page 39766]]

connecting wires; this chafing could result in an ignition source in 
the center fuel tank. ``Series 4'' (and subsequent series) probes, in 
contrast, incorporate a smooth-surface terminal block, nylon wire 
clamps, and a protective shrink-wrapped coating on the wires. 
Installation of ``series 4'' (or subsequent series) probes would 
prevent a potential in-tank ignition source due to incorrect terminal 
block configuration and resultant chafing damage to the wiring.
    The FAA's review of the design of the scavenge pump assembly of the 
Model 747 center fuel tank has identified its vulnerability to center 
fuel tank ignition as a result of a potential mechanical failure of the 
pump. This condition could cause a spark or flame front to emanate from 
the pump assembly, propagate through the pump inlet line, and ignite 
the fuel-air mixture inside the center fuel tank.
    Further, the FAA has become aware of numerous FQIS probe failures 
and system reliability problems in military applications. Subsequent 
investigation of Model 747 FQIS wiring has revealed the presence of 
corrosion, in the form of copper sulfur residue, on the affected probes 
and silver-plated copper wiring. This corrosion of the commonly used 
silver-plated copper wire is attributed to sulfur compounds inherently 
present in aviation fuels, bacterial growth, and the polysulfide 
sealant used in fuel tanks. Testing has demonstrated the potential for 
arcing and incandescing of copper sulfur residues at a given voltage, 
which could create a possible ignition source in the center fuel tank. 
A hot short failure in the FQIS outside of the fuel tank, in 
conjunction with the latent condition of excessive copper sulfur 
residue on probes or wiring inside the tank, could cause arcing or 
high-temperature leakage paths in fuel tanks. By contrast, nickel-
plated wires have been shown to exhibit little or no corrosion in this 
same environment.
    The unsafe conditions associated with damage to the center fuel 
tank wiring and other components described above, if not corrected, 
could result in ignition sources and consequent fire/explosion in the 
center fuel tank.

Wing Fuel Tanks vs. Center Fuel Tanks

    The actions identified by the FAA during the course of the ongoing 
accident investigation are part of continued activity to correct any 
design-or maintenance-related deficiencies in the Boeing 747 fuel tanks 
that may lead to the existence of an ignition source. This proposed AD 
focuses on the center fuel tanks only.
    Over the past 30 years, the service history for turbine-powered 
transport airplanes, excluding those used in military combat, has shown 
that in-flight explosions in wing fuel tanks occurred mainly when wide-
cut fuels or a mixture of wide-cut fuel and kerosene-type fuels were 
used. The FAA has considered several factors that may contribute to the 
significantly improved safety record of wing fuel tanks relative to 
center fuel tanks:
    1. On average, wing tank temperatures are lower than those in the 
center tanks because wing tanks have no significant on-airplane heat 
sources located in or near them, and the top and bottom surfaces of the 
wing tanks cool quickly as the airplane climbs into colder air.
    2. Except for immediately after landing, wing tanks usually contain 
a relatively large amount of fuel to act as a heat sink while the 
airplane is on the ground being heated by sunlight and ambient air, 
whereas center tanks are often empty or near empty on airplanes during 
operation; and
    3. Wing tank fuel pumps are normally operated with their pump 
inlets covered with fuel, which ensures that the wing tank pumps are 
always fuel-cooled during operation and mechanical sparks or high metal 
temperatures at the impeller cannot ignite vapor in the fuel tank.
    In general, the flammability of a fuel is dependent on the 
concentration of fuel/air mixture and the fuel temperature. As a 
function of temperature, the fuel/air mixture can be too lean for 
combustion (lower flammability limit) or too rich for combustion (upper 
flammability limit). For kerosene-type fuels such as Jet A, elevated 
fuel/air mixture temperatures increase the likelihood of the mixture 
being within the flammable range. Avoiding airplane operation with fuel 
temperatures in the flammable range reduces the fuel/air mixture's 
exposure to ignition in the presence of an ignition source.
    The unique environmental and operational conditions and service 
history information of fuel tanks show that the risk of an in-flight 
explosion is lower in wing fuel tanks than in center fuel tanks. 
Therefore, the FAA is not proposing to include the wing fuel tanks in 
this rulemaking activity.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 747-28-
2205, Revision 1, dated April 16, 1998. This service bulletin describes 
procedures for a visual inspection to detect discrepancies (damage, 
disbonding, and incorrect installation) of the center fuel tank wiring 
and components; and corrective actions, if necessary. Corrective 
actions involve repair or replacement of discrepant parts with new or 
serviceable parts. In addition, this service bulletin describes 
procedures for an electrical bonding test of the center fuel tank 
components, and reworking of any component with bonding outside 
specified maximum resistance limits.
    The FAA has reviewed and approved Boeing Alert Service Bulletin 
747-28A2208, dated May 14, 1998. This alert service bulletin describes 
procedures for:
     insulation resistance testing of the FQIS;
     visual inspection of the FQIS wiring and components to 
detect discrepancies (chafing damage to the wiring and incorrect 
configuration of the terminal blocks), and repair of discrepant 
components or replacement with new or serviceable components;
     replacement of ``series 3'' (or earlier series) FQIS 
probes with new ``series 4'' (or subsequent series) probes;
     retermination of the wires to the tank units and 
compensator, and replacement of FQIS wire bundle assemblies with new 
parts, if necessary;
     retesting (insulation resistance) of all components; and
     performing a system adjustment and a system operational 
test of the FQIS.
    The FAA also has reviewed and approved Boeing Alert Service 
Bulletin 747-28A2210, dated May 14, 1998. This alert service bulletin 
describes procedures for installation of a flame arrestor in the inlet 
line of the scavenge pump of the center fuel tank.

FAA's Determinations

    The FAA has examined the circumstances and reviewed all available 
information related to the accident and subsequent investigations. The 
FAA finds that, in addition to the actions specified in the service 
bulletins described previously, replacement of the Model 747 FQIS 
components (FQIS probes, compensator, and terminal strip) and wiring 
will reduce the risk of ignition in the center fuel tank, for the 
reasons described in the Discussion section above.
    The FAA has determined that repeated entry into the fuel tank will 
increase the risk of damage to in-tank components and systems. 
Moreover, extensive time and effort are required to access, purge, and 
close the fuel tank to accomplish each action proposed by this AD. 
Therefore, the FAA proposes a compliance time of 24 months to allow 
operators to concurrently perform all of the proposed actions in order 
to reduce

[[Page 39767]]

the risk of damage to the airplane from repeated entry. The proposed 
compliance time for accomplishment of the actions also would provide 
operators time for planning and scheduling, thus reducing the cost 
impact on the operators.
    The FAA is currently considering separate rulemaking to address 
long-term maintenance issues.

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:
    1. Performing a one-time visual inspection to detect damage, 
disbonding, and incorrect installation of the center fuel tank wiring 
and components; and repair or replacement, if necessary.
    2. Performing an electrical bonding test of the center fuel tank 
components; and rework, if necessary.
    3. For certain airplanes, performing an insulation resistance test 
of the FQIS and a one-time visual inspection to detect discrepancies of 
the FQIS; replacement of ``series 3'' (and earlier series) FQIS probes 
with new ``series 4'' (and subsequent series) FQIS probes; and 
corrective actions, if necessary.
    4. Replacing all FQIS components (FQIS probes, compensator, and 
terminal strip) with new components.
    5. Replacing silver-plated copper FQIS wiring with new nickel-
plated copper FQIS wiring.
    6. For certain airplanes, installing a flame arrestor into the 
inlet line of the scavenge pumps of the center fuel tank.
    The actions are required to be accomplished in accordance with the 
service bulletins (described previously), the 747 Maintenance Manual, 
or a method approved by the FAA.
    The proposed AD also would require that operators report inspection 
findings to the manufacturer.

Other Relevant Rulemaking

    Other fuel tank ignition scenarios have been studied by the FAA and 
have resulted in rulemaking action.
    On December 9, 1997, the FAA issued AD 97-26-07, amendment 39-10250 
(62 FR 65352, December 12, 1997), applicable to Boeing Model 747 series 
airplanes, which superseded AD 96-26-06, amendment 39-9870 (62 FR 304, 
January 3, 1997). AD 97-26-07 requires repetitive inspections of the 
Teflon sleeves that protect wiring to the boost pumps on the outboard 
main tanks on all Boeing 747 series airplanes. The Teflon sleeves are 
intended to protect the main tank boost pump wiring from chafing damage 
caused by the wires rubbing against each other or against the metal 
conduit that encases the wiring routed through the fuel tank. Chafing 
of these wires could lead to electrical arcing, which could potentially 
cause ignition of flammable vapors within the outboard wing fuel tanks. 
Similar action was taken on Model 737 series airplanes by telegraphic 
AD 98-11-52, issued May 14, 1998. The FAA is currently reviewing other 
Boeing airplane models to determine whether similar action is 
warranted.
    During the inspections required by AD 97-26-07, one operator 
discovered that the required Teflon sleeves were missing on one 
airplane. In response, on May 5, 1998, the FAA issued AD 98-10-10, 
amendment 39-10522 (63 FR 26063, May 12, 1998), to require all 
operators of Boeing 747 series airplanes to verify that the protective 
Teflon sleeves were installed on the main tank boost pump wiring. AD 
98-10-10 requires any operator discovering the absence of any Teflon 
sleeve on an airplane to perform corrective action prior to further 
flight.
    On November 26, 1997, the FAA issued a notice of proposed 
rulemaking (NPRM) (Docket 97-NM-272-AD) (62 FR 63624, December 1, 
1997), applicable to all Boeing Model 747-100, -200, and -300 series 
airplanes. This NPRM proposed a modification of the FQIS to incorporate 
separation, shielding, and/or electrical transient suppression features 
to prevent electrical signals with excessive energy from entering the 
fuel tanks. This action is intended to preclude electrical energy 
needed to produce ignition from entering the fuel tanks and will 
preclude the development of an ignition source within the FQIS if 
damage to wiring, corrosion, or other failures were to occur. On April 
14, 1998, the FAA issued a similar NPRM (Docket 98-NM-50-AD) (63 FR 
19852, April 22, 1998), for Boeing Model 737 series airplanes. The FAA 
is currently reviewing other Boeing airplane models to determine 
whether similar action is warranted.
    In addition, the FAA is addressing airplane fuel tank flammability 
issues with respect to the transport airplane fleet. On January 23, 
1998, the FAA established an Aviation Rulemaking Advisory Committee 
(ARAC) working group on fuel tank flammability reduction with the 
publication of a Notice of New Task Assignment in the Federal Register. 
This notice gives the ARAC working group until July 23, 1998, to 
provide the FAA and Joint Aviation Authority (JAA) with a report 
outlining specific recommendations and proposed regulatory text that 
will eliminate or significantly reduce the hazards associated with 
explosive vapors in the fuel tanks of transport category airplanes.
    As mentioned previously, the FAA also is considering rulemaking to 
require that each type certificate holder develop a fuel tank 
maintenance and inspection program, and that each operator have an FAA-
approved fuel system maintenance program. That proposal also would 
require a review of the original certification compliance findings to 
revalidate that failures within the fuel system will not result in 
ignition sources.

Cost Impact

    There are approximately 1,069 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 251 airplanes of U.S. 
registry would be affected by this proposed AD.
    The FAA estimates that it would take approximately 40 work hours 
per airplane to purge, access, and close the center fuel tank, at an 
average labor rate of $60 per work hour. The cost impact on U.S. 
operators to purge, access, and close the fuel tank is estimated to be 
$2,400 per airplane.
    The FAA estimates that the proposed inspection of the center fuel 
tank would be required to be accomplished on 251 airplanes. It would 
take approximately 56 work hours per airplane to accomplish the 
proposed inspection, at an average labor rate of $60 per work hour. 
Based on these figures, the cost impact of this proposed inspection on 
U.S. operators is estimated to be $843,360, or $3,360 per airplane.
    The FAA estimates that the proposed FQIS inspection and system 
operational test, probe replacement, and insulation resistance test 
would be required to be accomplished on 202 airplanes. It would take 
approximately 60 work hours (maximum) per airplane to accomplish the 
proposed FQIS inspection, at an average labor rate of $60 per work 
hour. Required parts would cost approximately $30,000 per airplane 
(maximum). Based on these figures, the cost impact of this proposed 
inspection on U.S. operators is estimated to be a maximum of 
$6,787,200, or $33,600 per airplane.
    The FAA estimates that the proposed installation of a flame 
arrestor would be required to be accomplished on 214 airplanes. It 
would take approximately 2 work hours per airplane to accomplish the 
proposed installation, at an average labor rate of $60 per work hour. 
Required parts would cost approximately $1,107 per airplane. Based on 
these figures, the cost impact of this proposed installation on U.S.

[[Page 39768]]

operators is estimated to be $262,578, or $1,227 per airplane.
    The FAA estimates that the proposed replacement of all FQIS 
components would be required to be accomplished on 251 airplanes. It 
would take approximately 24 work hours per airplane to accomplish the 
proposed replacement, at an average labor rate of $60 per work hour. 
Required parts would cost approximately $10,000 per airplane. Based on 
these figures, the cost impact of this proposed replacement on U.S. 
operators is estimated to be $2,871,440, or $11,440 per airplane.
    The FAA estimates that the proposed replacement of the FQIS wiring 
would be required to be accomplished on 251 airplanes. It would take 
approximately 24 work hours per airplane to accomplish the proposed 
replacement, at an average labor rate of $60 per work hour. Required 
parts would cost approximately $10,000 per airplane. Based on these 
figures, the cost impact of this proposed replacement on U.S. operators 
is estimated to be $2,871,440, or $11,440 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 98-NM-163-AD.

    Applicability: All Model 747 series airplanes, 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 (g) 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 prevent ignition sources and consequent fire/explosion in the 
center fuel tank, accomplish the following:
    (a) Within 24 months after the effective date of this AD, 
accomplish paragraphs (a)(1) and (a)(2), in accordance with Boeing 
Service Bulletin 747-28-2205, Revision 1, dated April 16, 1998.
    (1) Perform a visual inspection of the center fuel tank wiring 
and components to detect discrepancies (damage, disbonding, and 
incorrect installation). If any discrepancy is detected, prior to 
further flight, repair the discrepant component, or replace it with 
a new or serviceable component. And
    (2) Perform an electrical bonding test of the center fuel tank 
components. If any measured resistance exceeds the limit specified 
by Figure 1 of the service bulletin, prior to further flight, rework 
the discrepant component.

    Note 2: Revision 1 of Boeing Service Bulletin 747-28-2205 
provides two additional actions (inspection of the body fuel tank 
components and measurement of the ground resistance of the pressure 
switch case on the auxiliary power unit pump) that were not provided 
in the original version of this service bulletin. Inspections and 
testing accomplished prior to the effective date of this AD in 
accordance with Boeing Service Bulletin 747-28-2205, dated June 27, 
1997, are considered acceptable for compliance with the applicable 
actions specified in this AD.

    (b) Within 24 months after the effective date of this AD, 
perform an insulation resistance test of the fuel quantity 
indication system (FQIS), visual inspection of the FQIS wiring and 
components to detect discrepancies (chafing damage to the wiring and 
incorrect configuration of the terminal blocks), replacement of 
``series 3'' (or earlier series) FQIS probes with new ``series 4'' 
(or subsequent series) FQIS probes, and system adjustment and system 
operational test; as specified by paragraph (b)(1) or (b)(2) of this 
AD, as applicable; in accordance with Boeing Alert Service Bulletin 
747-28A2208, dated May 14, 1998. If any discrepancy is detected, 
prior to further flight, perform corrective actions in accordance 
with the alert service bulletin.
    (1) For Groups 1 and 2 airplanes, as listed in the alert service 
bulletin: Accomplish the inspection, testing, and corrective 
actions, as applicable, in accordance with Figure 2 of the alert 
service bulletin.
    (2) For Groups 3 and 4 airplanes, as listed in the alert service 
bulletin: Accomplish the inspection, testing, and corrective 
actions, as applicable, in accordance with Figure 3 of the alert 
service bulletin.
    (c) At the applicable time specified in paragraph (c)(1) or 
(c)(2) of this AD, submit a report of the results of the inspections 
required by paragraphs (a) and (b) of this AD, as applicable, to the 
Manager, Airline Support, Boeing Commercial Airplane Group, P.O. Box 
3707, Seattle, Washington 98124-2207. The report must include the 
information specified in Boeing Service Bulletin 747-28-2205, 
Revision 1, dated April 16, 1998 [for paragraph (a) of this AD]; and 
Boeing Alert Service Bulletin 747-28A2208, dated May 14, 1998 [for 
paragraph (b) of this AD]. Information collection requirements 
contained in this regulation have been approved by the Office of 
Management and Budget (OMB) under the provisions of the Paperwork 
Reduction Act of 1980 (44 U.S.C. 3501 et seq.) and have been 
assigned OMB Control Number 2120-0056.
    (1) For airplanes on which the inspections required by 
paragraphs (a) and (b) of this AD, as applicable, are accomplished 
after the effective date of this AD: Submit the report within 10 
days after performing the applicable inspection.
    (2) For airplanes on which the inspections required by 
paragraphs (a) and (b) of this AD, as applicable, have been 
accomplished prior to the effective date of this AD: Submit the 
report within 10 days after the effective date of this AD.
    (d) Within 20 years since date of manufacture, or within 24 
months after the effective date of this AD, whichever occurs later: 
Replace all center fuel tank FQIS components (FQIS probes, 
compensator, and terminal strip) with new FQIS components, in 
accordance with the 747 Maintenance Manual, chapters 28-11-00, 28-
41-00, 28-41-01, 28-41-02, and 28-41-09.

[[Page 39769]]

    (e) Within 20 years since date of manufacture, or within 24 
months after the effective date of this AD, whichever occurs later: 
Replace the silver-plated copper FQIS wiring of the center fuel tank 
with new nickel-plated copper FQIS wiring, in accordance with 747 
Maintenance Manual, chapters 28-11-00, 28-41-00, 28-41-01, 28-41-02, 
and 28-41-09.
    (f) For airplanes having line positions 1 through 971 inclusive: 
Within 24 months after the effective date of this AD, install a 
flame arrestor in the inlet line of the electrical motor-operated 
scavenge pump of the center fuel tank, in accordance with Boeing 
Alert Service Bulletin 747-28A2210, dated May 14, 1998.
    (g) 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 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (h) 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 July 15, 1998.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-19460 Filed 7-23-98; 8:45 am]
BILLING CODE 4910-13-U