[Federal Register Volume 64, Number 65 (Tuesday, April 6, 1999)]
[Rules and Regulations]
[Pages 16625-16635]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-8134]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-163-AD; Amendment 39-11106; AD 99-08-02]
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. The amendment 
requires a one-time inspection to detect discrepancies of the center 
fuel tank wiring and components, and corrective action, if necessary; 
and a one-time electrical bonding test of the center fuel tank 
components, and rework, if necessary. For certain airplanes, the 
amendment requires a one-time insulation resistance test and a one-time 
inspection to detect discrepancies of the wiring and components of the 
fuel quantity indication system (FQIS), and corrective actions, if 
necessary; replacement of certain FQIS probes with certain newer 
probes; a system adjustment and system operational test; and 
modification (installation of a flame arrestor) of the inlet line of 
the scavenge pump of the center fuel tank. This amendment is prompted 
by design review and testing results obtained in support of an accident 
investigation. The actions specified by this AD are intended to prevent 
ignition sources and consequent fire/explosion in the center fuel tank.

DATES: Effective May 11, 1999.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of May 11, 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: Dionne Stanley, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle

[[Page 16626]]

Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2250; 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 all Boeing Model 747 series 
airplanes was published in the Federal Register on July 24, 1998 (63 FR 
39765). That action proposed to 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, that action proposed to 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. That action was prompted by design review and testing 
results obtained in support of an investigation into a 1996 accident 
involving a Boeing Model 747 series airplane that occurred shortly 
after takeoff from John F. Kennedy International Airport in Jamaica, 
New York (hereinafter referred to as ``the accident'').
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

1. Support for Various Actions in the Proposal

    Five commenters support various actions proposed by the AD.
    Two commenters strongly support the philosophy in the notice of 
proposed rulemaking (NPRM) that tank entry would be minimized because 
multiple issues pertaining to the center wing tank may be accomplished 
during a single tank entry.
    One commenter states that it currently plans to accomplish the 
actions described in Boeing Service Bulletin 747-28-2205 during 
scheduled checks to inspect center wing tank components. Another 
commenter states that it considers a one-time inspection of all Model 
747 series airplanes necessary to ensure that no manufacturing or 
operator rework anomalies exist in today's fleet prior to the 
introduction of any new maintenance procedures. The FAA infers that 
those two commenters concur with the proposal to require the actions 
specified by Boeing Service Bulletin 747-28-2205, dated June 27, 1997, 
and Revision 1, dated April 16, 1998, as applicable.
    Four commenters concur with the proposal to require the actions 
contained in Boeing Alert Service Bulletin 747-28A2208, dated May 14, 
1998.
    Four commenters concur with the proposal to require the actions 
contained in Boeing Alert Service Bulletin 747-28A2210, dated May 14, 
1998.

2. Request To Withdraw the Proposal: No Justification

    One commenter states that, without any proof that the FQIS or any 
of the other center wing tank components may have been the cause of the 
accident, and, without any service experience that supports such a 
conclusion, there is no technical or operational justification to 
mandate the proposed rule. The FAA infers that the commenter requests 
withdrawal of the proposed AD.
    The commenter states that on-airplane tests performed by Boeing 
have not shown any in-service condition that could create any hazard. 
The commenter also concludes that there is no service experience that 
shows any evidence of ignition sources (evidence that would have been 
visible on any of the 248 airplanes that have been inspected).
    The FAA does not concur that the proposed AD should be withdrawn 
based on the lack of conclusive evidence that the accident was caused 
by failure of the FQIS components or any of the other center fuel tank 
components. The FAA agrees that no conclusive evidence exists to 
indicate the accident was caused by failure of the FQIS or center fuel 
tank components. However, during such accidents, evidence that could 
lead to a conclusive identification of the cause of the accident often 
is destroyed. Regardless of the degree of destruction caused by such an 
accident, there often is no specific physical evidence of low energy 
electrical arcing. In consideration of the extensive wiring installed 
on a Boeing Model 747 series airplane, and the extensive damage to the 
wiring that occurred during the airplane fire, breakup, and subsequent 
recovery, conclusive identification of a specific wire that was damaged 
before the fire and breakup is extremely unlikely.
    Following the determinations that an explosion in the center fuel 
tank was the initial event in the breakup of the airplane in the 
accident, and that the fire was not caused by an external source such 
as a bomb or missile, the National Transportation Safety Board (NTSB) 
has necessarily used systems analysis methods to determine what systems 
on the airplane are most likely to have been the source of ignition 
energy. That analysis included examinations of system failure modes and 
effects, service history, and similar airplanes. It was that analysis 
that led the FAA to propose the requirements specified in the NPRM.
    The same commenter stated that on-airplane tests performed by 
Boeing have not shown any in-service condition that could create any 
hazard, and that any evidence of ignition sources would have been 
visible on any of the 248 airplanes that have been inspected. The FAA 
surmises that the commenter is referring to the bonding and grounding 
checks recommended in Boeing Service Bulletin 747-28-2205. The FAA 
agrees that to date none of the bonding and grounding checks have 
revealed severe bonding or grounding degradation that would pose a 
safety threat to the airplane. The bonding and grounding provisions 
within the fuel tank are designed to protect the fuel system components 
from becoming in-tank ignition sources in the event of a lightning 
strike or static electricity. However, the investigation of the 
accident identified certain fuel tank explosion scenarios involving 
latent failures or aging conditions within the fuel tank that are not 
related to the bonding or grounding aspects of the fuel system. Those 
scenarios involve a failure or condition inside the tank (such as 
conductive debris, copper/sulfur or silver/sulfur contaminants, and 
damaged in-tank wiring) in combination with a failure outside the tank 
(such as a hot short or electrical interference condition on the FQIS 
wiring). Examples of these in-tank and out-of-tank conditions, which 
can contribute to a multiple-failure ignition scenario, were found in 
airplane service records and on airplanes that were inspected by the 
FAA and NTSB.
    The FAA does not agree with the commenter's conclusion that 
evidence of ignition sources would have been visible on any of the 248 
airplanes that have been inspected. The FAA surmises that the commenter 
is referring to the results of the inspections described in Boeing 
Service Bulletin 747-28-2205. The infrequency of fuel tank explosions 
on Model 747 series airplanes indicates that the conditions creating 
the scenario for an airplane fuel tank explosion are uncommon. To date 
no evidence of ignition sources or conditions that may lead to an 
ignition source have been identified through inspections described in 
Service Bulletin 747-28-2205; therefore, the FAA would expect this 
evidence or condition to be unusual. A

[[Page 16627]]

sample inspection of 200 or 300 airplanes may identify degradation or 
system aging issues, but the FAA has determined that only a thorough 
inspection of all affected Model 747 series airplanes in the fleet can 
determine if a rare condition setting the stage for an airplane fuel 
tank explosion exists in a given airplane. No change to the final rule 
in this regard is necessary.

3. Request To Withdraw the Proposal: Unnecessary

    One commenter states that the proposed AD is unnecessary due to the 
related rulemaking proposed in NPRM docket 97-NM-272-AD. The FAA infers 
that the commenter requests that this proposed AD be withdrawn.
    The commenter observes that the related proposed AD (97-NM-272-AD) 
would prevent possible voltage spikes caused by lightning, 
electromagnetic interference, or electrical failures from entering the 
fuel tanks. The commenter concluded that ignition sources would be 
eliminated by either the related NPRM or this proposed AD, and that 
mandating both proposals is unnecessary.
    NPRM docket 97-NM-272-AD has been issued as final rule AD 98-20-40 
(63 FR 52147, September 30, 1998), effective November 4, 1998. AD 98-
20-40, applicable to all Boeing Model 747-100, -200, -300, SP, and SR 
series airplanes, requires the installation of shielding and separation 
of the FQIS electrical wiring.
    The FAA does not concur with the commenter's rationale as a basis 
to withdraw the proposed AD. Although the FAA agrees that both this 
final rule and AD 98-20-40 address the potential for ignition sources 
within airplane fuel tanks, each activity addresses different aspects 
of the multiple-failure ignition scenarios identified by the NTSB and 
FAA in the course of the accident investigation. These different 
aspects of the multiple-failure ignition scenarios were identified 
through the FQIS safety analysis and examinations of Model 747 series 
airplanes performed by the NTSB and FAA and involve latent failures or 
aging conditions within the fuel tank combined with a subsequent single 
failure or electrical interference condition outside the tank.
    In attempting to preclude future fuel tank explosions, the FAA 
finds it necessary to address all aspects of viable ignition scenarios 
to ensure that potential failures of the fuel system cannot contribute 
to ignition of the flammable fuel vapors in airplane fuel tanks. By 
requiring ``best practices'' to be used both inside the tank (to 
eliminate the possibility for the creation of latent ``spark-gap'' 
locations in the event of high voltage on the FQIS wires) and outside 
the tank (to avoid introduction of ignition energy onto the FQIS 
wires), the FAA has determined that the modifications of the FQIS 
design of the Model 747 series airplane required by AD 98-20-40 and 
this final rule will adequately address the identified unsafe condition 
and meet the appropriate fail-safe standards to provide the level of 
safety (i.e., tank ignition events should never occur) intended by the 
regulations in place at the time of the original certification of the 
design.
    No change to the final rule in this regard is necessary.

4. Request To Remove Requirement To Inspect Wiring

    Five commenters request that the proposed AD remove the requirement 
to inspect the center fuel tank wiring and components, as specified by 
Boeing Service Bulletin 747-28-2205. One commenter, the manufacturer, 
states that Service Bulletin 747-28-2205 was initiated as a voluntary 
inspection activity. The service bulletin specifies that the purpose of 
inspecting the center fuel tank is to gather data on the in-service 
condition of fuel tanks, identify follow-up activities to ensure 
continued airworthiness, and develop updated maintenance programs and/
or corrective action service bulletins where necessary. The 
manufacturer stated that, because the purpose of the inspections 
identified in the service bulletin was to collect data necessary to 
assess the in-service condition of the fleet, only a sampling of 
airplanes would be required. The manufacturer adds that, since no 
unsafe conditions have been identified in the approximately 283 
airplanes inspected in accordance with this bulletin, there is no 
justification for mandating this bulletin. The manufacturer's 
philosophy has been to address any corrective actions for known issues 
in separate service bulletins to keep this bulletin from being mandated 
by regulatory action.
    Four commenters agree that the intent of Service Bulletin 747-28-
2205 was to conduct a sample program to gather data on in-service 
airplanes and not to address any unsafe condition.
    Two commenters also note that, on all airplanes inspected to date, 
there have been no immediate safety concerns identified. One commenter 
states that, based on the inspections performed to date, Boeing is 
still convinced that the present design is safe.
    The FAA does not concur with the commenters' request to withdraw 
the subject requirement. While the commenters state that Service 
Bulletin 747-28-2205 was initiated as a voluntary data-gathering 
inspection activity and that the manufacturer's philosophy has been to 
address any corrective actions for known issues in separate service 
bulletins, the FAA has repeatedly stated (e.g., at the NTSB Public 
Hearing and at ATA meetings) that it would consider mandating 
accomplishment of Service Bulletin 747-28-2205.
    The FAA agrees that to date none of the inspections have revealed 
severe bonding or grounding degradation or a specific condition that 
would pose a safety threat to affected airplanes. The infrequency of 
fuel tank explosions on Model 747 series airplanes indicates that the 
conditions creating the scenario for such an explosion are uncommon. To 
date no evidence of ignition sources or conditions that may lead to an 
ignition source has been identified through inspections performed in 
accordance with Service Bulletin 747-28-2205; therefore, the FAA 
expects this evidence or condition to be unusual. While the FAA agrees 
that a sample inspection of 200 to 300 airplanes may identify 
degradation or system aging issues, only a thorough inspection of all 
affected Model 747 series airplanes in the fleet can determine if a 
rare condition setting the stage for an airplane fuel tank explosion 
exists in a given airplane. Therefore, the FAA does not concur with the 
commenters' request to withdraw the requirement to inspect the center 
fuel tank wiring in accordance with Service Bulletin 747-28-2205.
    No change to the final rule in this regard is necessary.

5. Request To Add an Inspection

    One commenter requests that the proposed actions specified in 
Boeing Service Bulletin 747-28-2205 be expanded to include an 
inspection to ensure that only fuel tube clamps of proper design are 
used in the center fuel tank and that the electrical resistances of all 
fuel tube clamps and couplings are within specified limits.
    The commenter states that the NTSB, FAA, and National Aeronautics 
and Space Administration have each documented cases of fuel tube clamps 
and flexible fuel tube (Wiggins) couplings that were not properly 
bonded. In addition, the commenter found four different types of fuel 
tube clamps present in Model 747 series airplanes, some of which were 
not bonded. Also, the commenter has found fuel tube clamps in the 
center fuel tank of a Model 747 series airplane with silicon cushions 
that had degraded in

[[Page 16628]]

the presence of fuel. The commenter further notes that military 
specifications prohibit the use of this type of clamp in fuel tanks.
    The FAA does not concur with the commenter's request to add an 
inspection. At the NTSB's request, an operator measured resistances and 
capacitances from three airplanes, each a different model, utilizing 
flexible fuel tube (Wiggins) couplings. The data from those 
measurements can be found in the NTSB accident investigation docket 
associated with the subject accident. After a review of the data from 
each of the three airplanes, the FAA determined that the range of 
resistances and capacitances measured would not result in an ignition 
with respect to static charge. The fuel tube clamps would be even less 
of a concern than the Wiggins fittings (for which the data were taken) 
because the fuel tube clamps would have lower associated capacitances.
    While previous examination of the Wiggins coupling design has 
identified the potential for generating electrical sparks during a 
lightning event, standard installations in large aluminum fuel tanks 
(as in the Model 747) with fay surface bonding where fuel tubes attach 
to wing structure and the use of bonding jumpers have been shown to 
provide adequate lighting protection. In that type of installation, the 
design relies on the bonding jumper and fay surfaces to create a path 
for conducting the lightning current. The requirement to examine the 
bonding jumpers and measure the electrical bonding resistance as 
specified in Boeing Service Bulletin 747-28-2205, Revision 1, verifies 
the integrity of the provisions for lightning protection. Therefore, no 
additional measurements or inspections concerning the Wiggins couplings 
themselves are required.
    Previous studies performed regarding the threat of lightning to an 
aircraft fuel system have not identified tube clamps as ignition 
sources.
    No change to the final rule in this regard is necessary.

6. Request To Revise Reporting Requirements

    Several commenters request revision or withdrawal of the proposed 
requirements to report results of the inspection of the center fuel 
tank and FQIS wiring. The specific requests are as follows:
     One commenter requests that the proposed requirement to 
report results of the inspection specified by Boeing Service Bulletin 
747-28-2205 be withdrawn. The commenter states that the reporting 
requirement is necessary only for providing sample results to aid in 
defining future maintenance requirements. The commenter also is 
concerned that legible and consistent reporting results are not always 
obtained during inspections. The commenter states that it would be of 
considerable concern if corrupt or lost data meant that an operator was 
noncompliant.
     Three commenters request that the proposed inspection 
reporting requirements be modified to allow 30 days instead of the 
proposed 10 days. One commenter, the manufacturer, requests that the 
proposed AD extend the reporting time from 10 to 30 days because the 
volume and detail of the records taken during the inspection require a 
significant effort to collect and document. In addition, some airlines 
perform a series of inspections on a number of airplanes within a short 
time frame. One commenter, an operator, states that 10 days is not 
adequate to provide the reports, based on numerous center fuel tank 
inspections it has performed (in accordance with Service Bulletin 747-
28-2205). That commenter adds that the data for the inspection are 
quite extensive, and that collating and processing the data take 
considerable time; in some cases, three weeks were required to input 
the data into a database and complete a qualitative report.
     One commenter opposes any proposed requirement to 
reinspect airplanes inspected previously with the original issue of 
Boeing Service Bulletin 747-28-2205, due to the change in reporting 
requirements in Revision 1 of that service bulletin. One commenter, an 
operator, states that the reporting mechanism in the original release 
of Service Bulletin 747-28-2205 was improved in Revision 1 (the main 
purpose of the revision). The commenter observed that operators did 
provide the relevant data to Boeing, but not necessarily in a manner 
consistent with the mechanism employed in Revision 1 of the service 
bulletin.
     Two commenters request that, for those airplanes on which 
the center fuel tank inspections have already been accomplished in 
accordance with the original version of Boeing Service Bulletin 747-28-
2205, the proposed reporting requirements be revised to allow any 
incorrect or missing data to be obtained and submitted after a 
scheduled tank entry or ``C'' check, prior to the compliance date of 
the proposed AD. One commenter, an operator, explained that when the 
original data from the center fuel tank inspections (in accordance with 
the original release of Service Bulletin 747-28-2205) were collected, 
the inspection was not a mandatory project. Although most of the data 
were collected, about 1% to 4% of the data were missing or incorrect on 
13 of 44 airplanes inspected. That commenter interprets the proposed 
requirement to submit all findings on the previously inspected 
airplanes to mean that operators would be required to plan another 
unscheduled tank entry to re-obtain the missing measurements. That 
commenter plans to obtain the missing measurements during the 
accomplishment of the installation of the scavenge pump flame arrestor 
and considers an additional tank entry prior to that installation to be 
of no value.
    The FAA concurs with the request to remove the reporting 
requirements from the proposal. Because the proposed AD specified that 
the reporting results of the inspections described in both Service 
Bulletin 747-28-2205 and Alert Service Bulletin 747-28A2208 be sent 
directly to the manufacturer, the FAA would not be reviewing those 
results. Boeing Service Bulletin 747-28-2205 states that the data from 
the inspection program ``* * * will be used to confirm the intended 
condition of the tanks and, where necessary, to identify follow-up 
activities to assure the continued airworthiness of these tanks. These 
additional activities may include updated maintenance programs and/or 
corrective action service bulletins.'' Service Bulletin 747-28A2208 
states that ``* * * data will be collected and used to confirm the 
intended conditions of the FQIS * * *''
    Ordinarily, the FAA mandates that inspection results be submitted 
directly to the agency when the FAA intends to use the data to 
determine if the AD needs to be revised. For example, data reporting 
may be mandated if that information could be used to identify trends 
indicating that the AD would need a more restrictive action, such as 
including additional airplanes or reducing the compliance time. 
Inspection data from 283 Model 747 series airplanes have been submitted 
by operators having already completed the actions specified by the 
original issue of Service Bulletin 747-28-2205. These data have not 
identified any information that the FAA would consider relevant to the 
requirements of the proposed AD. The FAA does not expect that any data 
from Alert Service Bulletin 747-28A2208 will identify information 
relevant to the requirements of the proposed AD. Because additional 
data from the accomplishment of either Boeing Service Bulletin 747-28-
2205 or Alert Service Bulletin 747-28A2208 would not serve a direct 
purpose for the FAA, the reporting requirements have

[[Page 16629]]

been removed from the final rule. Operators may voluntarily submit 
their inspection and test data to the manufacturer, as requested in the 
applicable service bulletins.
    The final rule has been revised to delete paragraph (c), which 
referred to the reporting requirements for the inspections and tests 
contained in Boeing Service Bulletin 747-28-2205 and Alert Service 
Bulletin 747-28A2208.

7. Support for Reporting Requirement

    One commenter fully supports a requirement for operators to report 
findings to the FAA. [However, it should be noted that the reporting 
requirement proposed in the NPRM would have required operators to ``* * 
* submit a report of the results of the inspections * * * to the 
Manager, Airline Support, Boeing Commercial Airplane Group.'']
    It was not the FAA's intent to require that the inspection reports 
be submitted to the FAA. As stated earlier, ordinarily, the FAA 
mandates that reporting requirements be submitted directly to the 
agency when the FAA intends to use the data to determine if the AD 
needs to be revised. For example, data reporting may be mandated if 
that information could be used to identify trends indicating that the 
AD would need a more restrictive action, such as encompassing more 
airplanes or a shorter compliance time. Inspection data from 283 Boeing 
Model 747 series airplanes have been submitted by operators having 
already completed the original version of Boeing Service Bulletin 747-
28-2205. These data have not identified any information that the FAA 
would consider relevant to the requirements of the proposed AD. The FAA 
does not expect that any data from Alert Service Bulletin 747-28A2208 
will identify information relevant to the requirements of the proposed 
AD. Because additional data from the accomplishment of either service 
bulletin would not serve a direct purpose to the FAA, the reporting 
requirements for Boeing Service Bulletin 747-28-2205 and Alert Service 
Bulletin 747-28A2208 will be removed from the final rule. The operators 
may voluntarily submit their inspection and test data to the 
manufacturer.
    The reporting requirements [paragraph (c) of the proposed AD] have 
been removed from the final rule.

8. Request To Allow Optional Modification

    One commenter explained that, during inspections performed on 
airplanes in accordance with the original version of Boeing Service 
Bulletin 747-28-2205, some operators, with the airplane manufacturer's 
approval, modified in-tank bonding by adding additional bonding 
jumpers. The operator states that the modifications have been necessary 
for various reasons, but always with the intent to ensure conformity 
with design requirements, and that, at the next ``D'' check, the 
airplane may or may not be reworked back to original configuration, 
depending upon the circumstances of the modification.
    The commenter requests that the final rule consider the 
aforementioned situation so that operators do not have to re-enter the 
fuel tanks.
    The FAA infers that additional bonding jumpers were installed to 
achieve the resistance values specified by the airplane type design. 
The FAA additionally infers that the operators are concerned that, 
because the addition of bonding jumpers is not specified as acceptable 
rework in the service bulletin, re-entry into the fuel tank would be 
required to achieve the resistance values by a method specified in the 
service bulletin. The FAA considers that the bonding jumpers added with 
the approval of the manufacturer may be an acceptable change to the 
type design. However, requests for alternative methods of compliance 
must be submitted in accordance with paragraph (d) of this AD. 
(Operators of foreign-registered airplanes would need to obtain 
approval for the change from their respective regulatory authorities as 
an alternative method of compliance to the AD.) Another option would be 
for the manufacturer to revise Service Bulletin 747-28-2205 to add this 
modification, and apply for an alternative method of compliance to the 
AD. No change to the final rule is necessary.

9. Request To Remove Certain Airplanes From the Requirement To 
Accomplish Paragraph (a)

    One commenter requests that, for new airplanes, the FAA mitigate 
the intent of paragraph (a) of the proposed AD, ``unless it is clearly 
the intent of the FAA to document compliance with SB 747-28-2205 during 
production.''
    The commenter interprets paragraph (a) of the NPRM to mean that new 
production airplanes also would be required to accomplish the proposed 
inspections and tests during production, or that the operators would be 
required to perform the inspections and tests after delivery, but no 
later than 24 months after the effective date of the proposed AD. 
Therefore, at the time of delivery, airplane records would be required 
to demonstrate compliance with Boeing Service Bulletin 747-28-2205 or 
an FAA-approved equivalent method of compliance. Otherwise, the AD 
compliance letter, provided at the time of new airplane delivery, would 
be required to report the AD as further action required by the customer 
after delivery.
    The FAA concurs with the commenter's interpretation of the effect 
paragraph (a) of the proposal would have on production airplanes. 
However, the intent of the proposal was not to require the 
incorporation of Service Bulletin 747-28-2205 for the production 
airplanes. Paragraph (a) of the final rule has been revised to require 
accomplishment of Service Bulletin 747-28-2205, Revision 1, by 
airplanes listed in that service bulletin.

10. Request To Revise Work Hour Estimates

    One commenter stated that the airplane downtime provided in the 
referenced service bulletins is not a true reflection of the time 
necessary to accomplish the actions, as it does not include tank 
preparation, scheduling manpower, and any necessary rework.
    The commenter suggests that the rework associated with the actions 
described in the original version of Boeing Service Bulletin 747-28-
2205 takes as least as long as the inspection itself. Although no 
specific change was requested by the commenter, the FAA infers that the 
commenter requests that the work hour estimates for the wiring 
inspection be revised.
    The FAA does not concur with the request to revise the work hour 
estimates. While the FAA agrees that the service bulletins do not 
include tank preparation time, the cost estimate for the AD does factor 
in the preparation time and associated cost for one center fuel tank 
entry (assuming that all of the required actions will be accomplished 
concurrently). Normally the cost analysis in AD rulemaking actions does 
not include ``incidental costs,'' such as planning time or time 
necessitated by other administrative actions. Because incidental costs 
may vary significantly from operator to operator, such costs are almost 
impossible to calculate.
    Furthermore, the economic analysis of the AD is limited only to the 
cost of actions actually required by the rule. It does not consider the 
costs of ``on condition'' actions, such as repairing damaged components 
detected during a required inspection (``repair, if necessary''). Such 
``on condition'' repair actions would be required to be accomplished--
regardless of AD action--in order to correct an unsafe

[[Page 16630]]

condition identified in an airplane and to ensure operation of that 
airplane in an airworthy condition, as required by the Federal Aviation 
Regulations.
    No change to the final rule in this regard is necessary.

11. Request To Revise Cost Estimate

    One commenter provided cost estimates different from those proposed 
in the NPRM, including $12,500 for the work hours, $61,000 for the 
material, and $69,000 for the downtime required to accomplish the 
proposed actions, for a total of $142,500 per airplane. Although there 
was no specific change requested by the commenter, the FAA infers that 
the commenter requests that the proposed cost estimates be revised.
    The FAA does not concur with the request to revise the cost 
estimates. The commenter did not provide any justification for the 
different cost estimate.
    Moreover, the FAA considers it inappropriate to attribute the costs 
associated with aircraft ``downtime'' to the cost of the AD, because, 
normally, compliance with the AD will not necessitate any additional 
downtime beyond that of a regularly scheduled maintenance hold. 
However, in cases such as this AD, where additional downtime may be 
necessary for some airplanes, the FAA does not possess sufficient 
information to evaluate the number of airplanes that may be so affected 
or the amount of additional downtime that may be required. Therefore, 
attempting to estimate such costs would be futile.
    No change to the final rule in this regard is necessary.

12. Request To Mandate Accomplishment of Unreleased Service 
Bulletin

    One commenter requests that the proposed rule be modified to 
mandate the actions contained in a revision to Boeing Alert Service 
Bulletin 747-28A2208.
    The commenter advised that a revision to the alert service bulletin 
was being prepared. The commenter listed the changes to be included in 
the revision:
     A clarification of the part numbers for sleeving material 
and wire;
     A clarification in references to the supplier service 
bulletin on the compensators, and additional information provided to 
operators on the installation of a seal boot during the assembly of a 
splice; and
     A clarification of a reference with respect to the 
installation of terminals lugs.
    The FAA does not concur with the commenter's request to mandate the 
actions contained in a revision to Alert Service Bulletin 747-28A2208 
because the revision will not be released in time to support the 
procedural schedule for the release of this AD. Use of the phrase ``or 
later FAA-approved revisions'' violates Office of the Federal Register 
regulations regarding approval of materials that are incorporated by 
reference. However, affected operators may apply for an alternative 
method of compliance, in accordance with paragraph (d) of this AD.

13. Request To Expand Inspection Requirements

    One commenter requests that the proposed FQIS inspection (actions 
as described in Boeing Alert Service Bulletin 747-28A2208) be expanded 
to include the following actions that were identified during the 
accident investigation:
     Electrical tests for disconnected/floating wire shielding 
that has been found inside and outside Boeing Model 747 fuel tanks;
     A test for proper operation of the FQIS indicator light 
circuit (a failure path was found from the light circuit to the tank 
wires);
     Isolation of FQIS and Airborne Integrated Data System 
wiring; Inspections for loose metal debris on and in the volumetric 
shutoff (ground refueling) unit that can bridge across FQIS compensator 
circuits; and
     Inspections of the wiring connections at all terminal 
blocks and terminal strips in the center fuel tank.
    The FAA does not concur with the commenter's request to expand the 
FQIS inspection in this AD. The FAA points out that the proposed AD is 
intended to address only in-tank actions. However, some of the 
commenter's proposed actions concerning systems or components outside 
of the fuel tanks are addressed in AD 98-20-40 [airplane models not 
addressed by that AD will be addressed by a proposed Special Federal 
Aviation Regulation (SFAR)]. AD 98-20-40 requires the installation of 
shielding and separation of the electrical wiring of the FQIS and the 
first four bulleted items in the preceding list.
    The commenter also proposes that the FAA require electrical tests 
for disconnected or floating wire shielding inside the fuel tanks. The 
action specified in the NPRM for accomplishing Boeing Alert Service 
Bulletin 747-28A2208 requires a visual inspection of the FQIS wire 
shield termination at the terminal blocks, which, according to the 
commenter, should detect any loose or disconnected wire shields. 
However, the commenter adds that, with the new requirement to replace 
all FQIS wiring outside of the fuel tanks and the surge tank (the tank 
located on the outboard tip of each wing, which collects any overfill 
from any of the fuel tanks) with shielded wire, the concern regarding a 
floating or disconnected wire shield within the fuel tank (in the FQIS) 
is mitigated.
    The FAA does not concur with the request to include electrical 
tests for disconnected or floating wire shields inside the center fuel 
tank. With the mandated design change requiring shielding on all 
outside-the-tank FQIS wiring, a hot short to the FQIS wire bundle 
outside of the tank would be intercepted and grounded by the FQIS wire 
bundle shield. Therefore, the only threat posed by a floating or 
disconnected wire shield inside the fuel tank, such as the HI Z shield, 
would be system malfunctioning due to potential electromagnetic 
effects. While system malfunctioning is undesirable, it does not pose a 
safety threat to the airplane with respect to fuel tank ignition.
    The commenter also proposes inspections of the wiring connections 
at all terminal blocks and terminal strips in the center fuel tank. The 
FAA points out that paragraph (b) of the AD requires ``a one-time 
visual inspection of the FQIS wiring and components, in accordance with 
Boeing Alert Service Bulletin 747-28A2208.'' Included in that alert 
service bulletin are specific procedures for the inspection of all 
terminal blocks and terminal strips in the center fuel tank; this 
inspection is required for compliance with the requirements of this AD. 
The FAA agrees that an action to visually inspect the terminal strip 
located in the center wing tank for proper wiring connections is 
appropriate. The final rule does not require revision in this regard.

14. Request To Remove In-Production Airplanes From Inspection 
Requirement

    One commenter requests that, for new airplanes, the FAA mitigate 
the intent of paragraph (b) of the proposed AD, ``unless it is clearly 
the intent of the FAA to document compliance with SB 747-28A2208 during 
production.''
    The FAA does not concur with the commenter's request. The AD, as 
written, does not require documentation of compliance with Boeing Alert 
Service Bulletin 747-28A2208 for production airplanes. Paragraphs 
(b)(1) and (b)(2) of the AD specify those groups listed in the airplane 
effectivity section of the service bulletin, which includes only 747-
100, -200, -300, SR, and SP airplane line

[[Page 16631]]

numbers. Therefore, none of the 747-400 production airplanes would be 
required to comply with paragraph (b) of this AD. No change to the 
final rule is necessary in this regard.

15. Request To Limit FQIS Inspection Requirement to Younger 
Airplanes

    One commenter requests the FAA to revise the requirement to inspect 
the FQIS wiring by limiting it to airplanes younger than 20 years. The 
commenter observes that mandating the combination of the inspection of 
the FQIS wiring and components and the replacement of the FQIS wiring 
and components is overdone for airplanes older than 20 years. If 
rulemaking requires removal of FQIS wiring and components, an extra 
inspection on the newly installed components cannot be technically 
justified.
    The FAA concurs with the commenter's statement that requiring both 
the FQIS wiring inspection and probe replacement in accordance with 
Boeing Alert Service Bulletin 747-28A2208 and the replacement of FQIS 
wiring and components for airplanes older than 20 years is not 
technically justified. If both requirements were to be mandated, 
airplanes that are required to replace FQIS wiring and components would 
not be subject to the inspection described in Alert Service Bulletin 
747-28A2208. However, as discussed in issue 18., the requirement to 
replace FQIS wiring and components has been removed.

16. Request To Eliminate Duplicate Inspection

    Three commenters state that the proposal would require a 
duplication of the wiring inspection of the FQIS. (The same inspection 
is described in Boeing Service Bulletin 747-28-2205 and Alert Service 
Bulletin 747-28A2208.) The commenters request that the AD clarify this 
requirement so that operators may avoid the duplication of work.
    The FAA concurs with the commenters' request. Service Bulletin 747-
28-2205 and Alert Service Bulletin 747-28A2208 do indeed contain some 
duplicate actions. Therefore, the final rule has been revised to 
continue to require accomplishment of Boeing Alert Service Bulletin 
747-28A2208 for the FQIS inspection for Model 747-100, -200, -300, SP, 
and SR series airplanes. Airplanes already inspected in accordance with 
Steps 1 through 9 in Figure 11 of the original issue of Service 
Bulletin 747-28-2205, will receive credit for the accomplishment of 
Steps 1 through 6 in Figure 16 of Alert Service Bulletin 747-28A2208. 
Model 747-100, -200, -300, SP, and SR series airplanes will be required 
to accomplish only step 3 in Figure 11 of Service Bulletin 747-28-2205, 
Revision 1. However, because Alert Service Bulletin 747-28A2208 does 
not address Model 747-400 airplanes, those airplanes would be required 
to perform the tasks outlined in Steps 1 through 9 in Figure 11 of 
Service Bulletin 747-28-2205, Revision 1.

17. Request To Remove Requirement To Install Flame Arrestor

    Three commenters do not support the requirement to accomplish 
Boeing Alert Service Bulletin 747-28A2210, which describes installation 
of a flame arrestor in the inlet line of the scavenge pump. Two 
commenters request the FAA to provide valid technical data and further 
technical discussion in support of that requirement.
    One commenter stated that neither service experience over the past 
25 years of operation of the Model 747 nor findings of the 248 
airplanes inspected to date indicate that the scavenge pump design 
could possibly create an unsafe condition. The commenter states that, 
other than providing an additional layer of safety, there is no 
technical justification to mandate the actions specified in Alert 
Service Bulletin 747-28A2210.
    The other commenters note that, while the FAA identified the 
scavenge pump's vulnerability to center fuel tank ignition as a result 
of a potential mechanical failure of the pump, Alert Service Bulletin 
747-28A2210 specifies that ``laboratory testing of the pump has not 
revealed any condition under which the pump would generate an ignition 
source.'' The commenters question the necessity for the proposed 
modification due to the disparity between the FAA and Boeing positions. 
The commenters suggest that the FAA pursue further examination of this 
issue and provide valid technical data supporting the need for this 
modification.
    The FAA infers that the commenters are requesting removal of the 
requirement to install a flame arrestor in the scavenge pump inlet line 
of the center fuel tank. The FAA does not concur. It was noted during 
the accident investigation that, although the structure that had 
contained the scavenge pump was recovered, the scavenge pump itself was 
missing from the wreckage. The scavenge pump is operated differently 
than the other pumps within the fuel system. The purpose of the 
scavenge pump is to reduce the amount of unusable fuel in the center 
fuel tank by scavenging the fuel left in the tank after the override 
boost pumps have been turned off (due to low pressure output). This 
scavenged fuel is relocated to a wing tank for later use. Because of 
its unique operation, the scavenge pump is run dry, which means that it 
continues to operate while exposed only to the fuel vapor within the 
center fuel tank.
    Because the scavenge pump was missing and unavailable for further 
analysis, the NTSB reviewed possible failure scenarios associated with 
the vane-type scavenge pump. The scavenge pump rotating element is made 
of steel, as are the pump vanes and sleeving against which the vanes 
rotate. While the laboratory testing performed on Boeing Model 747 
scavenge pumps has not produced an ignition during explosion-proof 
testing and dry-running the pump, not all of the potential failures are 
represented by those types of qualification tests. One scenario not 
represented by qualification tests involves metallic debris within the 
tank being drawn into the pump and becoming lodged between the steel 
pump sleeve and the steel rotating components, or causing another type 
of pump failure. This scenario could cause sparking or excessive heat 
and potentially act as an ignition source if the pump were exposed to 
fuel vapors from within the center fuel tank (dry-running). The 
vulnerability of the scavenge pump to creating a scenario that would 
allow ignition of the flammable fuel vapors drawn into the pump and 
have the resultant flame front propagate back through the inlet line to 
the center fuel tank causing a fuel tank explosion was identified 
during the design reviews of this component. That revelation led to the 
manufacturer's willingness to provide a flame arrestor design for the 
inlet line of the scavenge pump. Therefore, the FAA considers this 
information as technical justification for requiring the installation 
of a flame arrestor in the inlet line of the scavenge pump.
    No change in the final rule is required.

18. Request To Remove Requirement To Replace FQIS: No Demonstrated 
Need

    Five commenters oppose the FAA's proposal to require replacement of 
the center tank FQIS components and wiring on Model 747 series 
airplanes having 20 or more years of service. The FAA infers that these 
commenters request removal of these replacement actions from the 
proposed AD.
    Four commenters state that there is no evidence to date indicating 
that sulfide contamination is degrading these specific parts to a point 
where they would be considered a safety hazard to

[[Page 16632]]

the airplane, either by themselves or in combination with system 
failures.
    One commenter notes that it has conducted analyses and tests on 
these particular FQIS components that were removed from aged Boeing 
Model 747 series airplanes and reports it has not found an instance in 
which the level of sulfide contamination presents a hazard. The 
commenter also states that it provided an extensive response to this 
issue of sulfides in its response to NPRM (docket) 97-NM-272-AD. The 
commenter notes that the FAA and NTSB are actively pursuing studies of 
sulfides and the effect these compounds may have in the fuel tank. The 
commenter proposes that, prior to rulemaking activities on this issue, 
further research into the subject of sulfides in fuel tanks be 
accomplished and suggests that these investigations pursue the 
mechanisms for the formation of sulfides in commercial fuel tank 
environments. The commenter further states that any testing should 
involve, where practical and possible, actual airplane components and 
wiring, and study of the ignition capability of sulfide-contaminated 
equipment in a fuel vapor environment.
    One commenter states that there are no data that indicate that a 
replacement of the FQIS installed on Model 747-400 series airplanes is 
necessary. The commenter points out that there are significant 
differences in the design and construction of the FQIS components and 
wiring for Model 747-400 and 747 Classic series airplanes.
    The FAA concurs with the request to remove the requirement to 
replace the FQIS. The FAA agrees with the commenters that the effects 
of copper/sulfur contaminates are not fully understood at this time. 
The FAA had anticipated gathering meaningful data from the commenters 
as to a reasonable replacement time for the FQIS components and wiring, 
but no additional data were provided through this comment process. 
Therefore, the FAA may consider further rulemaking on the issue of 
copper/sulfur or silver/sulfur contamination.
    The FAA and NTSB currently plan to research the effects of copper/
sulfur deposits on fuel tank system components. The research will 
include identifying copper/sulfur film properties, identifying the 
mechanisms related to film growth, and identifying aircraft maintenance 
methods that will detect and remove deposits before they reach 
hazardous levels.
    The final rule has been revised to remove the requirement to 
replace all the center tank FQIS components with new FQIS components 
[paragraph (d) of the NPRM]. The final rule has been further revised to 
remove the requirement to replace the silver-plated copper FQIS wiring 
with nickel-plated copper wiring [paragraph (e) of the NPRM].

19. Request To Remove Requirement To Replace FQIS Wiring: Various 
Reasons

    Several commenters propose the removal of the requirement to 
replace the FQIS wiring and components, for various reasons. As stated 
previously, the final rule has been revised to remove the requirement 
to replace all the center tank FQIS components with new FQIS 
components. The action requiring replacement of the silver-plated 
copper FQIS wiring with nickel-plated copper wiring also has been 
removed from the final rule. Therefore, these requests are moot.

20. Request To Reduce Compliance Time

    One commenter does not support the proposed compliance time to 
replace the FQIS components, and to replace silver-plated copper FQIS 
wiring with new nickel-plated wiring, on airplanes having 20 or more 
years of service. The commenter encourages the FAA to require a much 
earlier replacement interval.
    The commenter states that the proposed actions are based on finding 
the presence of corrosion, in the form of copper/sulfur residue, on 
center fuel tank FQIS components of Model 747 series airplanes. The 
commenter further states that testing has demonstrated the potential 
for arcing of sulfur residues, which could create a possible ignition 
source. However, the commenter has found sulfidation on FQIS components 
in a 17-year-old Boeing Model 757 series airplane that had accumulated 
only 24,000 hours of service. The commenter is also aware of Boeing 
laboratory test results (which were shared with the FAA) that indicate 
that sulfidation may be present on FQIS components with less than 1,000 
hours of service.
    As discussed previously, the FAA acknowledges that the effects of 
copper/sulfur contaminates are not fully understood at this time. The 
FAA had anticipated gathering meaningful data from the commenters to 
help determine a reasonable replacement time for the FQIS components 
and wiring, but no additional data were provided through this comment 
process. Therefore, the FAA may consider further rulemaking on the 
issue of copper/sulfur or silver/sulfur contamination.
    The FAA and NTSB currently plan to research the effects of copper/
sulfur deposits on fuel tank system components. The research will 
include identifying copper/sulfur film properties, identifying the 
mechanisms related to film growth, and identifying airplane maintenance 
methods to detect and remove deposits before they reach hazardous 
levels. After this research is accomplished, appropriate actions and 
intervals for those actions may be proposed to address any concerns 
identified by the research.
    As previously stated, the final rule has been revised to remove the 
requirements to replace all center tank FQIS components with new FQIS 
components, and to replace silver-plated copper FQIS wiring with 
nickel-plated copper wiring.

21. Request To Require Replacement of All Silver-Plated Wiring

    One commenter strongly supports the action for replacing silver-
plated copper FQIS wiring in the center wing tank with new nickel-
plated wiring. The commenter encourages the FAA to expand this action 
to address replacement, with new nickel-plated copper wiring, of all 
silver-plated copper wiring (not just that on the FQIS) that is exposed 
to fuel or fuel vapors.
    The FAA does not concur with the commenter's proposal. The FAA 
acknowledges that the effects of copper/sulfur contaminates are not 
fully understood at this time. The FAA had anticipated gathering 
meaningful data from the commenters to determine a reasonable 
replacement time for the FQIS components and wiring, but no additional 
data were provided through this comment process. Therefore, the FAA may 
consider further rulemaking on the issue of copper/sulfur or silver/
sulfur contamination.
    The FAA and NTSB currently plan to research the effects of copper/
sulfur deposits on fuel tank system components. The research will 
include identifying copper/sulfur film properties, identifying the 
mechanisms related to film growth, and identifying airplane maintenance 
methods to detect and remove deposits before they reach hazardous 
levels. After this research is accomplished, appropriate actions and 
intervals for those actions may be proposed to address any concerns 
identified by the research.
    As previously stated, the final rule has been revised to remove the 
requirement to replace all center tank FQIS components with new FQIS 
components. In addition, the final rule has been revised to remove the 
requirement to replace silver-plated copper FQIS wiring with nickel-
plated copper wiring.

[[Page 16633]]

22. Request To Approve BF Goodrich FQIS for Compliance

    One commenter, an operator, requests that the AD specify the BF 
Goodrich Digital FQIS system as an acceptable means of compliance with 
the AD. The operator reports that it expects to have the FQIS system 
installed on all of its airplanes by January 2000.
    The FAA is reviewing the BF Goodrich Digital FQIS system to 
determine if it is an acceptable means of compliance with AD 98-20-40, 
which requires the installation of shielding and separation of the 
electrical wiring of the FQIS. The FAA does not have the information 
necessary to approve the BF Goodrich Digital FQIS system as an 
alternative method of compliance to the requirements of the proposed 
AD.
    Furthermore, as stated previously, the final rule has been revised 
to remove the requirement to replace the FQIS components and wiring due 
to concerns regarding copper/sulfur or silver/sulfur contamination.

23. Request To Revise Number of Affected Airplanes

    One commenter, the manufacturer, provided an estimate of affected 
airplanes for United States and foreign operators. The FAA infers that 
the commenter requests the revision of the affected number of airplanes 
to reflect 248 airplanes operated domestically and a total of 1,077 
airplanes operated worldwide.
    The FAA concurs. The original estimates in the proposed AD were 
provided by the manufacturer. Because the manufacturer provided a 
revised estimate via the NPRM comment process, the final rule has been 
revised to reflect these numbers.

24. Request To Extend Compliance Time

    Five commenters request an extension of the compliance time for the 
actions specified by the proposed AD.
    Two commenters suggest 36 months as a realistic compliance time, 
considering the time required to schedule these modifications into 
operators' normal maintenance schedules.
    One commenter proposes that, although parts will be available to 
support the modification described in Boeing Alert Service Bulletin 74-
28A2210, the compliance time should be the same for all actions. The 
commenter is concerned that requiring a different compliance time for 
this service bulletin could mean that the 40-hour effort of tank 
preparation would be required for only a two-hour modification 
procedure. Therefore, this commenter requests the compliance time for 
all actions to be 36 months.
    One commenter requests an increase in the compliance time to allow 
operators to complete these actions at scheduled ``D'' checks, which 
would reduce the additional ``down time'' of the airplanes. The 
commenter encourages the FAA to consider the additional cost associated 
with taking an airplane out of service.
    Another commenter, an operator, stated that a proposed compliance 
time of 24 months would require most of its airplanes to be inspected/
modified in ``C'' checks. The associated cost of accomplishing these 
actions in ``C'' checks rather than ``D'' checks is $69,000 per 
airplane.
    Some commenters request that the compliance time associated with 
replacement of the FQIS components be based on a time frame of ``x'' 
months after parts availability.
    Another commenter suggests that, with respect to the proposed 
requirement to replace all of the FQIS components, a period not to 
exceed 25 years after manufacture of the airplane would be better 
matched to the airplane operational life and maintenance schedule.
    The FAA does not concur with the commenters' request for an 
extension of the compliance time. In developing an appropriate 
compliance time, the FAA considered the safety implications, parts 
availability, and normal maintenance schedules for timely 
accomplishment of the required actions. The FAA also has removed from 
the final rule several proposed actions: replacement of all center tank 
FQIS components with new FQIS components, replacement of silver-plated 
copper FQIS wiring with nickel-plated copper wiring, and the reporting 
requirements. These revisions to the AD will substantially reduce the 
amount of time operators will need to accomplish the required actions. 
Also, because replacement of the FQIS components and wiring will no 
longer be required, the parts availability concern associated with the 
fact that those system components are no longer in production or do not 
currently exist is not a factor in considering compliance time.
    Because the proposed AD addresses actions to reduce the potential 
for an ignition source within the center fuel tank, and because some of 
the original requirements in the proposed NPRM have been removed, the 
FAA does not find it is in the best interest of the public or industry 
to extend the compliance time. Associated rulemaking regarding ignition 
sources, such as a proposed SFAR (which is currently being developed) 
and AD 98-20-40 (which has a 36-month compliance time), will not be 
fully implemented for several years. Therefore, it is important that 
the actions required by this AD be implemented as quickly as possible.
    No change to the compliance times in the final rule is necessary.

Additional Changes to Final Rule

    Certain requirements in the proposed AD would have been applicable 
to all Boeing Model 747 series airplanes; those actions have been 
removed from the final rule. As a result, the applicability of the 
final rule has been revised to include only those airplanes affected by 
the remaining requirements.
    In the proposed AD, paragraphs (a)(2), (b)(1), and (b)(2) referred 
to certain Figures in the applicable service bulletins. The FAA finds 
that clarification of the requirements of paragraphs (a)(2), (b)(1), 
and (b)(2) is necessary. Although the Figures called out in those 
paragraphs contain the primary instructions for those actions, 
additional information may be found in other Figures of the service 
bulletins for accomplishment of the actions required by those 
paragraphs. The final rule has been revised to remove specific Figure 
references from paragraphs (a)(2), (b)(1), and (b)(2).

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 1,077 Boeing Model 747 series airplanes of 
the affected design in the worldwide fleet. The FAA estimates that 248 
airplanes of U.S. registry will be affected by this AD.
    The FAA estimates that it will 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 inspection of the center fuel tank will 
be required to be accomplished on 248 airplanes. It will take 
approximately 56 work hours per airplane to accomplish the inspection, 
at an average labor rate of

[[Page 16634]]

$60 per work hour. Based on these figures, the cost impact of this 
inspection on U.S. operators is estimated to be $833,280, or $3,360 per 
airplane.
    The FAA estimates that the FQIS inspection and system operational 
test, probe replacement, and insulation resistance test will be 
required to be accomplished on 191 airplanes. It will take 
approximately 60 work hours (maximum) per airplane to accomplish these 
actions, at an average labor rate of $60 per work hour. Required parts 
will cost approximately $30,000 per airplane (maximum). Based on these 
figures, the cost impact of these actions on U.S. operators is 
estimated to be a maximum of $6,417,600, or $33,600 per airplane.
    The FAA estimates that the installation of a flame arrestor will be 
required to be accomplished on 214 airplanes. It will take 
approximately 2 work hours per airplane to accomplish the installation, 
at an average labor rate of $60 per work hour. Required parts will cost 
approximately $1,107 per airplane. Based on these figures, the cost 
impact of this installation on U.S. operators is estimated to be 
$262,578, or $1,227 per airplane.
    The cost impact figures discussed above are 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.

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:

99-08-02  Boeing: Amendment 39-11106. Docket 98-NM-163-AD.

    Applicability: Model 747 airplanes having line numbers 1 through 
1124 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 prevent ignition sources and consequent fire/explosion in the 
center fuel tank, accomplish the following:
    (a) For those airplanes listed in Boeing Service Bulletin 747-
28-2205, Revision 1, dated April 16, 1998: Within 24 months after 
the effective date of this AD, accomplish paragraphs (a)(1) and 
(a)(2) of this AD, in accordance with the service bulletin.
    (1) Perform a one-time 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 a one-time electrical bonding test of the center 
fuel tank components. If any measured resistance exceeds the limits 
specified by 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.
    Note 3: Airplanes required to accomplish paragraph (b) of this 
AD are exempt from accomplishing steps 1, 2, and 4 through 9 in 
Figure 11 of Boeing Service Bulletin 747-28-2205, Revision 1, dated 
April 16, 1998.

    (b) For those airplanes listed in Boeing Alert Service Bulletin 
747-28A2208, dated May 14, 1998: Within 24 months after the 
effective date of this AD, perform a one-time insulation resistance 
test of the fuel quantity indication system (FQIS), a one-time 
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; in accordance with the alert service bulletin. If any 
discrepancy is detected, prior to further flight, perform corrective 
actions in accordance with the alert service bulletin.

    Note 4: For airplanes on which steps 1 through 9 in Figure 11 of 
Boeing Service Bulletin 747-28-2205, dated June 27, 1997, or 
Revision 1, dated April 16, 1998, were accomplished prior to the 
effective date of this AD, steps 1 through 6 in Figure 16 of Boeing 
Alert Service Bulletin 747-28A2208, dated May 14, 1998, are not 
required.

    (c) 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.
    (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 5: 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 747-28-2205, Revision 1, dated April 16, 1998; Boeing Alert 
Service Bulletin 747-28A2208, dated

[[Page 16635]]

May 14, 1998; and Boeing Alert Service Bulletin 747-28A2210, dated 
May 14, 1998; as applicable. 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 May 11, 1999.

    Issued in Renton, Washington, on March 29, 1999.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-8134 Filed 4-5-99; 8:45 am]
BILLING CODE 4910-13-U