[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