[Federal Register Volume 64, Number 99 (Monday, May 24, 1999)]
[Rules and Regulations]
[Pages 27905-27911]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-12690]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 98-NM-383-AD; Amendment 39-11175; AD 99-11-05]
RIN 2120-AA64
Airworthiness Directives; Boeing Model 737 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 all Boeing Model 737 series airplanes, that requires
repetitive displacement tests of the secondary slide in the dual
concentric servo valve of the power control unit (PCU) for the rudder,
and replacement of the valve assembly with a modified valve assembly,
if necessary. This amendment is prompted by reports of cracking found
in PCU secondary servo valve slides. The actions specified by this AD
are intended to prevent failure of the secondary slide and consequent
rudder hardover and reduced controllability of the airplane.
DATES: Effective June 28, 1999.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of June 28, 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: R.C. Jones, Aerospace Engineer,
Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane
Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue,
SW., Renton, Washington 98055-4056; telephone (425) 227-1118; 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 737 series
airplanes was published in the Federal Register on January 13, 1999 (64
FR 2161). That action proposed to require repetitive displacement tests
of the secondary slide in the dual concentric servo valve of the power
control unit (PCU) for the rudder, and replacement of the valve
assembly with a modified valve assembly, if necessary.
Interim Action
This is considered interim action until final action is identified,
at which time the FAA may consider further rulemaking.
Opportunity To Comment
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
Support for the Proposed Rule
Several commenters express support for the proposed rule.
1. Requests To Extend the Initial Compliance Time
Several commenters request that the initial compliance time be
extended for the displacement test. While the proposed rule specifies
an initial compliance time of 4 months for certain airplanes, the
commenters suggest extensions of the initial compliance time ranging
from an initial compliance time of 8 months to an initial compliance
time of 2 years. The following identifies justifications provided by
the commenters for increasing the compliance time:
Some of the commenters state that testing and analysis to
date indicate that the servo valve of the PCU can sustain the highest
loads expected to occur in the normal service life of the Model 737
fleet of airplanes. The testing and analysis also indicate that a
single valve leg crack still permits the PCU to function normally for
periods of time much greater than the proposed 4-month compliance time.
Other commenters assert that an inadequate number of
qualified repair facilities exist, and that the number of PCU's in the
fleet are inadequate to permit compliance with the proposed AD. To meet
the compliance time for the 3,000 and more PCU's that would require
testing would likely ground a significant number of airplanes.
Two commenters state that the financial implications of
meeting the proposed compliance time could result in bankruptcy of one
or more small airlines.
One commenter states that the shipping time alone, without
consideration of any other factors, would prevent operators from
completing the displacement tests within the compliance time specified
in the proposal.
Several commenters state that all spares facilities are at
maximum use and spare PCU's are all being used in order to comply with
the requirements of AD 97-14-04, amendment 39-10061 (62 FR 35068, June
30, 1997).
Another commenter states that the turnaround time for
replacing units not modified in accordance with AD 97-14-04 is
approximately 30 to 45 days. Such turnaround time for those units would
prevent some operators from complying within the proposed compliance
time.
One other commenter expresses a serious concern that
accomplishment of all the testing done in the limited time proposed (4
months) could result in the introduction of various maintenance errors
that would possibly introduce a new unsafe condition.
The FAA concurs that the initial compliance time for accomplishment
of
[[Page 27906]]
the displacement test can be extended. Further, the FAA has reviewed
certain testing that indicates that valve slides with cracks can meet
the control valve limit and ultimate load requirements as well as
survive numerous life cycles. Additionally, the FAA has reviewed the
results of analyses that indicate valves with single cracks can
withstand an interval greater than the proposed 4-month interval. While
the testing and analyses results are not definitive proof that a second
crack will not develop, the results are evidence that valves with
single cracks are safe in-service for a limited interval. The FAA also
acknowledges that the number of PCU's in the fleet and the number of
qualified repair facilities may not be adequate to permit compliance
for the fleet within 4 months. In light of this information, the FAA
has determined that the compliance time of paragraphs (a)(1), (a)(2),
and (a)(3) of this AD can be extended to 16 months. The final rule
reflects this change.
2. Requests To Extend the Repetitive Displacement Testing Intervals
One commenter requests that the repetitive testing intervals be
extended from 12,000 to 12,800 flight hours to coincide with a major
check in the Boeing Maintenance Planning Document. Another commenter,
the airplane manufacturer, requests that the interval be extended from
12,000 to 24,000 flight hours. Both commenters state that the
displacement testing interval should coincide with scheduled heavy
maintenance to preclude an undue burden on operators and to reduce any
potential maintenance errors.
The FAA concurs that the repetitive testing interval may be
extended from 12,000 to 24,000 flight hours. The FAA finds that, based
on results of testing and analysis (referred to in comment 1. of this
AD), extending the testing interval will not adversely affect the
safety of the fleet. Additionally, the FAA concurs that, in this case,
less chance of maintenance errors will occur if the testing is
accomplished during scheduled heavy maintenance. Paragraph (b) of this
AD has been revised to specify an interval of 24,000 flight hours for
the repetitive displacement testing.
3. Requests To Withdraw the Proposed Rule
One commenter, the airplane manufacturer, states that there is no
technical data to support the position that ``an unsafe condition is
likely to exist or develop'' as stated in the proposed rule. The
commenter states that, on the other hand, the FAA's concern of a
possible condition developing into a ``thru-crack'' condition on both
the 1st leg and the 2nd leg of the secondary slide clevis is based on a
hypothetical and unsubstantiated extrapolation of failures. Further,
the commenter states that, although it agrees that ``thru-cracking'' of
both the 1st leg and 2nd leg of the secondary slide clevis would be an
unsafe condition, the commenter strongly disagrees that such a
condition exists in service or that it is likely to develop while the
slide is installed in a rudder PCU. The commenter also asserts that,
based on the results of testing and analyses by both the airplane
manufacturer and the PCU manufacturer, the secondary slide is not
susceptible to cracking after installation in the PCU. The commenter
concludes that the only plausible cause of cracking of the secondary
slides is slide mishandling or in-process damage.
Another commenter states that testing and analyses performed by
both the airplane manufacturer and PCU manufacturer indicate that
sufficient redundancy is provided in the rudder system to operate
almost 18 lifetimes with one broken leg of the secondary slide.
Additionally, the commenter asserts that, even in a worst-case scenario
of both legs of the secondary slide having a thru-fracture, and a piece
of material causing both primary and secondary slides to jam that
results in full rudder deflection, sufficient controllability of the
airplane would be ensured by the rudder pressure limiting device
required by AD 97-14-03.
The FAA infers that the commenters are requesting that the proposed
rule be withdrawn. The FAA does not concur. The root cause of the
cracked servo control valves of the PCU has not been determined. The
only way these cracks have been duplicated so far is by dropping or
hammering the secondary valve slide. The FAA considers it unlikely that
all of the 12 control valves had been dropped or hammered, which
suggests that there may be additional factors that make the secondary
valve slide susceptible to cracking. This may indicate that lower load
phenomena (and possibly normal handling) may be responsible for the
cracking. The lack of complete information makes it essential that the
valve slides be removed from the fleet. Additionally, a single crack in
the secondary control valve slide clevis reduces the load bearing
redundancy of the valve to a single load path. Loss of the remaining
load path could result in uncommanded rudder motion to a hardover
position.
The bases of the design of the control system on Boeing Model 737
series airplanes is that no single failure shall result in an unsafe
condition, and that either loss of a single redundant mechanism will be
detectable or the remaining redundant mechanism will survive for the
life of the airplane. It is generally accepted by the affected
operators and the FAA that some valves, possibly up to 50 valves, in
the fleet are cracked. Some airplanes may be reduced to single-thread
systems. Additionally, the rudder pressure-limiting device does not
reduce pressure on the Model 737 ``classic'' airplanes at altitudes
below 1,000 feet on takeoff or below 750 feet during landing. During
those particular conditions, uncommanded rudder motion to a hardover
condition may be catastrophic. In light of these findings, the FAA has
determined that the requirements of this AD are appropriate and
necessary.
4. Request To Eliminate Paragraph (a)(2) of the Proposed Rule
Another commenter states that requiring performance of the
displacement test [as specified in paragraph (a)(2) of the proposal]
prior to installation of the PCU required by AD 97-14-04 will have a
negative effect in the ability of operators to accomplish compliance
with that AD. The commenter points out that the resources and units
from the spares pool will be consumed in the effort to comply with the
proposed rule. In addition, the commenter states that the wording of
the proposal could be interpreted to mean that those PCU's installed
prior to the effective date need to be removed and re-tested, even
though they could have already been tested. The FAA infers that the
commenter is requesting that paragraphs (a)(2) and (c) of the proposal
be removed.
The FAA concurs that paragraph (a)(2) of the proposal should be
deleted. The FAA considers that it would be more efficient for an
operator to install a PCU that is in compliance with AD 97-14-04 and
this final rule, but acknowledges that it could prohibit an operator
from installing a serviceable unit that complies with AD 97-14-04
simply because the displacement test required by this final rule had
not been accomplished. Therefore, the FAA has deleted paragraph (a)(2)
of this AD and revised paragraph (a)(1) to remove the phrase ``prior to
the effective date of this AD.'' Paragraph (a)(1) of this AD now
applies to all Model 737-100, -200, -300, -400, and -500 series
airplanes regardless of whether AD 97-14-04 is incorporated before or
after the effective date of this AD. Additionally, the FAA
[[Page 27907]]
has renumbered the sub-paragraphs of paragraph (a) of this AD to
reflect the deletion of paragraph (a)(2) of this AD. The FAA also has
revised paragraph (c) of this AD to specify that only PCU's that have
completed a successful displacement test, as signified by the letter
``C'' after the serial number, may be installed as of 16 months after
the effective date of this AD. See Item 5. of this AD for further
discussion of the revision of paragraph (c) of this AD.
5. Request To Revise Paragraph (c) of the Proposed Rule
One commenter, the airplane manufacturer, requests that the wording
of paragraph (c) of the proposal be revised. The commenter states that
the current wording stating that no person shall install a main rudder
PCU on any airplane unless that PCU's nameplate has been vibro-engraved
with the letter ``C'' following the serial number of the PCU should be
revised to specify ``with the letter C' or greater.'' The commenter
states that by adding the words ``or greater,'' it allows for the
possibility of future revisions to the PCU. Additionally, the commenter
points out that if ``or greater'' is not added, it would mean that
installing a newer version PCU would not comply with the requirements
of the proposal.
The FAA concurs for the reasons submitted by the commenter and has
revised paragraph (c) of the final rule accordingly. In addition, the
FAA has extended the compliance time requirement for this paragraph to
``as of 16 months after the effective date of this AD.'' The FAA has
determined that, in light of the data supporting the increase of the
initial and repetitive compliance times required for the displacement
testing and the fact that there could be a shortage of available
spares, extending the compliance time of paragraph (c) to correspond
with the initial compliance time for the displacement testing is
appropriate.
6. Requests To Revise the Reporting Requirements
Two commenters request that the reporting requirements of paragraph
(d) of the proposed AD be revised. One of these commenters requests
that the reporting requirement for the initial displacement testing
should be revised to 10 days for those failed control valves that fail
the initial displacement test and 30 days for those control valves that
pass the initial displacement testing. No justification for that
request was provided. The other commenter requests deletion of the
requirement to report results for control valves that pass the
repetitive displacement tests. The commenter states that limiting the
reporting data to those control valves that fail any repetitive
displacement testing will provide all the necessary data for analysis.
The commenter points out that eliminating the requirement to report
control valves that pass the displacement testing of the repetitive
inspections would reduce the burden to operators, as well as to the
FAA.
The FAA concurs that reporting only PCU's that fail repetitive
displacement testing will provide adequate information to determine the
secondary valve slide condition after extended in-service time. The FAA
considers that, in the interest of relieving some burden on the
operators, the reporting times for all displacement testing may be
extended from 10 days to 30 days. The FAA finds that extending the
reporting time will not adversely affect safety. The FAA has revised
paragraph (d) of this AD to reflect these changes.
7. Request To Revise Corrective Action
One commenter requests that paragraph (b)(2) of the proposed rule,
which requires accomplishment of corrective action in accordance with a
method approved by the Manager, Seattle Aircraft Certification Office,
be revised. The commenter states that the only corrective action
available to operators is to replace the dual servo valve with a valve
that passes the displacement test. Therefore, the commenter asserts
that it is unnecessary to require approval of corrective actions from
the FAA.
The FAA concurs for the reason given by the commenter. Paragraph
(b)(2) of the final rule has been revised to specify that the
corrective action (replacement of the dual servo valve with a valve
that passes the displacement test) shall be accomplished in accordance
with the applicable alert service bulletin.
8. Request To Add Precautionary Language
Two commenters request that the FAA add wording to the proposed
rule to specify that only properly trained maintenance personnel and
appropriate repair facilities are used to accomplish the displacement
testing and replacement of the valve assemblies specified in the
proposal. The commenters state that, in the past, it appears that some
repair stations did not have proper facilities or properly trained
personnel, and maintenance errors were made. The commenters assert that
the disassembly and testing are complex and require special maintenance
knowledge and special equipment. The commenters request that
precautionary language specifying that only appropriately trained
personnel and appropriate maintenance facilities may be used to
accomplish the requirements of this AD be added to the proposal to
preclude the risk of maintenance errors.
The FAA does not concur with the commenters' request to include the
requested precautionary language in the final rule. The FAA
acknowledges that displacement testing and replacement of the valve
assemblies specified in this final rule may be complex and may require
special maintenance knowledge and special equipment. However, existing
maintenance regulations and guidance should ensure that appropriate
personnel perform maintenance and that appropriate equipment and repair
facilities are used.
9. Request To Clarify Compliance With Testing Requirements
One commenter requests that the proposal be revised to clarify that
vibro-engraving the letter ``C'' on the serial number constitutes
compliance that the unit has met the requirements of the AD and that no
further testing is required. The commenter states that the
clarification is necessary because the proposal applies to airplanes by
line number and does not account for the possibility that a tested PCU
may be installed on an affected airplane.
The FAA acknowledges that some clarification is necessary. First,
this AD applies to all Boeing Model 737 series airplanes as stated in
the applicability of this AD, not just to airplanes that are specified
by certain line numbers. Second, the application of the letter ``C''
(or greater letters, see Item 5.) to the serial number of the PCU does
not mean that the PCU is in compliance with the full requirements of
this AD. Such application of the letter ``C'' or greater letters
constitutes only compliance with the requirements of the initial
displacement test. Third, the application of the letter ``C'' or
greater letters does not mean that no further testing is required. The
specific reasons for the repetitive testing requirements of this AD and
the consideration of these requirements as interim action is discussed
elsewhere in Item 12. of this AD. The FAA, however, concurs that
clarification may be necessary in paragraph (c) of this AD to ensure
that accomplishment of the application of the letter ``C'' or greater
letters does constitute compliance with the requirement to accomplish
the initial displacement test. Paragraph (c) of this AD has been
revised to clarify this point.
[[Page 27908]]
10. Request To Add New Service Information
One commenter, the airplane manufacturer, requests that both
Revisions 1 of Boeing Alert Service Bulletins 737-27A1221 and 737-
27A1222, both dated January 28, 1999, be added to the proposed rule as
appropriate sources of service information. The commenter states that
minor changes were made in the new alert service bulletins.
The FAA has reviewed and approved both Revisions 1 of the alert
service bulletins. The FAA has determined that the revised alert
service bulletins contain not only minor changes, but changes that
contain descriptive material that is clarifying in nature. Since those
revisions to not add any burden to operators, the FAA has revised
paragraphs (a) and (b) of the final rule to reflect both Revisions 1 of
the service bulletins as the applicable sources of service information
for this AD. The FAA also has revised the final rule by adding a new
NOTE 2 that specifies that accomplishment of the initial displacement
testing in accordance with earlier editions of the service bulletins is
acceptable for the initial displacement testing required by this AD.
11. Requests To Revise Cost Impact
Several commenters request that the cost impact information provide
more realistic estimates of the costs for affected airplanes. These
commenters request that the proposal include estimates of cost for such
items as: scheduling and administrating; removing and replacing of the
PCU, shipping of the PCU's; performing the displacement testing and the
full Acceptance Test Procedure (ATP) if completed by a third party; and
the estimated costs of performing the displacement testing
repetitively.
The FAA does not concur that the cost impact information should be
revised. The cost estimates provided in this AD represent the time
necessary to perform only the actions actually required by this AD. The
FAA recognizes that, in accomplishing the requirements of any AD,
operators may incur ``incidental'' costs in addition to the ``direct''
costs. The cost analysis in AD rulemaking actions, however, typically
does not include incidental costs, such as the time required to gain
access and close up; planning time; or time necessitated by other
administrative actions. Because incidental costs may vary significantly
from operator to operator, they are almost impossible to calculate.
The replacement of the valve assembly that the commenters refer to
are actions that must be accomplished in the event that the results of
the displacement testing are outside the limits specified in the
service bulletin. Typically, the economic analysis of an AD is limited
to the cost of actions actually required by the rule. It does not
consider the costs of ``on condition'' actions (that is, actions taken
to correct an unsafe condition if found), since those actions would be
required to be accomplished, regardless of AD direction, in order to
correct an unsafe condition identified in an airplane and to ensure
operation of that airplane in an airworthy condition, as required by
the Federal Aviation Regulations.
12. Request To Delete the ``Interim Action'' Section
One commenter, the airplane manufacturer, requests that the
``Interim Action'' section of the proposal be deleted. The commenter
states that there is no data to indicate that there continues to be any
diminished level of safety once the rudder PCU has successfully
completed a displacement test. The commenter concludes that there is no
known safety concern that will require a ``final action.'' The
commenter also requests that reference in the preamble of the proposal
to a final action not being identified yet be deleted. The commenter
asserts that satisfactory results of displacement testing is adequate
proof that cracking does not exist in the PCU.
The FAA does not concur; a final solution to terminate the required
repetitive displacement tests may be necessary. As stated previously,
12 cracked control valves have been reported to date. However, the root
cause for the cracking has not been positively determined. The only way
these cracks have been duplicated so far is by dropping or hammering
the secondary valve slide. The FAA considers it unlikely that all 12
control valves had been dropped or hammered. The FAA considers it more
likely that lower load phenomena (and possibly normal handling) may be
responsible for the cracking, which indicates that there may be
additional factors that make the secondary valve slide susceptible to
cracking. The lack of a root cause, varying sensitivity of different
control valves to cracking, and uncertainties associated with damage
tolerance analyses on the valve material indicates to the FAA that
valve design may not be adequate and that cracking may occur in the
future. The FAA does not consider that the results of a single
displacement test is proof that cracking will not eventually occur in
the PCU valve.
For the reasons stated above, the FAA does not concur that it is
unnecessary to specify that the FAA may consider further rulemaking. No
change to the final rule in this regard is necessary.
13. Requests To Allow Dye Penetrant Inspections
Several commenters request that dye penetrant inspections be
required instead of displacement testing. One commenter asserts that,
if a cracked valve has been dye penetrant inspected and found to be
free of cracking, no further displacement testing should be required.
This same commenter states that, since there are no delayed cracking
mechanisms involved, a previous dye penetrant inspection to detect any
cracking is sufficient. Another commenter states that dye penetrant
inspection actually detects cracking better than the displacement test.
That commenter states that the dye penetrant inspection is better
because it can detect all cracking and that accomplishment of a
displacement test could leave a valve installed that contains small
cracks. The commenter further asserts that completion of a dye
penetrant inspection should suffice as a terminating action for the
proposed actions.
The FAA does not concur that dye penetrant inspection should be
required in lieu of displacement testing. The FAA considers that dye
penetrant inspection techniques have varied levels of crack detection
capability. Some dye penetrant inspection techniques may not have the
capability to detect some cracking that can propagate to failure of a
single leg. Additionally, the displacement test is performed on an
assembled PCU. This ensures that secondary control valve is in its most
protected configuration, and that the secondary valve slide is not
subjected to further handling. Therefore, it is unnecessary to revise
the final rule in this regard.
14. Requests To Credit Dye Penetrant Inspections
Two commenters request that PCU's that have been inspected
previously with dye penetrant be exempt from the proposed requirement
to accomplish displacement testing. The commenters also request that,
at a minimum, the FAA increase the initial compliance time and
repetitive intervals of the proposed AD for those PCU valves that have
had a dye penetrant inspection. The commenters assert that, since the
cause of the valve cracking is due to handling prior to the valve
assembly,
[[Page 27909]]
accomplishment of a dye penetrant inspection and careful assembly
provide acceptable assurance that the control valve is not cracked and
does not need to be displacement tested.
The FAA does not concur with the commenters' request. The FAA finds
that PCU valves that have had a dye penetrant inspection must undergo
the displacement testing at the same initial and repetitive intervals
as the other valves. As discussed previously (Item 13.), dye penetrant
inspection techniques have varied levels of crack detection capability.
Some dye penetrant inspection techniques may not have the capability to
detect partial cracks that can propagate into a leg failure. The
displacement testing will detect partial cracking by causing the crack
to propagate to failure of a single leg. Additionally, after a dye
penetrant inspection is accomplished, the secondary control valve slide
is again subject to handling because the valve must be cleaned and
reassembled. The FAA considers that the increase in initial compliance
time (as discussed in Item 1.) and the intervals for the repetitive
displacement testing provided in this final rule should provide some
additional time for completing the displacement testing. No change is
necessary to the final rule in regard to dye penetrant inspection.
15. Request To Eliminate the Installation Requirements of AD 97-14-04
One commenter requests that the FAA suspend the requirement to
install PCU valves required by AD 97-14-04. The commenter states that
until the root cause of the secondary slide cracking is identified, the
PCU's required by AD 97-14-04 should not be installed.
The FAA does not concur. Although the root cause of the PCU valve
cracking has not been identified, testing and analysis indicate that a
cracked valve will perform its intended function for a certain period
of time. The repetitive displacement testing will identify any cracked
valves and facilitate their removal. The valves installed in accordance
with AD 97-14-04 eliminate design ``features'' that could lead to
potentially unsafe flight conditions (e.g., reversal, overstroke, and
high residual pressures). Therefore, the FAA considers the benefits of
continued incorporation of AD 97-14-04 to outweigh the risks of
secondary valve cracking. The FAA has determined that unless new
information develops that reveals evidence contrary to the need for the
implementation of the requirements of AD 97-14-04, those requirements
are still valid and necessary to ensure the operational safety of the
fleet. No change is necessary to the requirements of this final rule in
this regard.
16. Request To Add an Inspection to the Requirements of the Proposed
Rule
One commenter requests that the proposed rule be revised to add an
inspection for chipping in the area of the clevis. The commenter states
that a control valve that was removed from a kit had a particle missing
from the clevis end that appeared to be chipped off. Therefore, the
commenter states that it would be prudent to inspect for chipping to
ensure that other chipped valves are in the fleet.
The FAA does not concur that an inspection for chipping should be
added to the final rule. Although the FAA agrees that the valves in the
fleet should not be chipped, only one control valve that was chipped
has been detected. The FAA considers that the mechanism causing the
chip is independent of the cause of the cracking of control valves. If
an inspection requirement to the final rule increases the burden of the
operator, it would necessitate issuing a supplemental notice of
proposed rulemaking (NPRM) to permit public comment in accordance with
the Administrative Procedures Act (APA). The FAA has determined that
delay of the final rule is not warranted based on the identified unsafe
condition addressed in this rule. However, the FAA may consider
separate rulemaking to address the concern of possible chipped
secondary control valves.
17. Request To Remove Requirement To Test Slides Already in Service
The commenter states that slides currently installed on PCU's do
not need to be displacement tested. The commenter asserts that, once
control valves are installed, they are protected from damage. The
commenter concludes that the requirement to test slides already in
service should be deleted from the proposal.
The FAA does not concur. Even though slides installed on PCU's are
substantially protected, two issues exist that indicate that PCU's in
service need to be tested. One, a cracked valve was detected on a PCU
removed from service. Two, the root cause of the cracking and
sensitivity to cracking has not been established. Since the FAA finds
that all cracked control valves must be removed from the fleet, all
valves that are installed must be tested. No change to the final rule
is necessary in this regard.
18. Request To Postpone Requirements Until a Terminating Action is
Provided
One commenter, an airline operator, requests that the FAA define a
terminating action for the repetitive displacement tests required by
the proposed AD. The commenter states that time should be allotted to
find a terminating action in order to reduce the risk of errors
occurring from repeating displacement testing. The FAA infers that the
commenter is requesting that the requirements specified in the proposal
be postponed until a terminating action is provided.
The FAA does not concur that additional time to develop and approve
a terminating action is warranted to delay issuance of this final rule.
The FAA has determined that the identified unsafe condition must be
addressed even though the terminating action has not been developed and
approved yet. The FAA, however, has been advised that a design
improvement of the clevis of the secondary control valve slide that is
not susceptible to cracking may be currently in development. Once a
design is reviewed and approved by the FAA, further rulemaking may be
considered as specified in the ``Interim Action'' section of this AD.
19. Request To Revise the Initial Compliance Time
One commenter requests that the FAA revise the initial compliance
time for the displacement testing from the proposed 4 months to 120
days. The commenter states that correction of the identified unsafe
condition addressed by the proposal is critical to flight safety.
The FAA does not concur that the compliance time should be revised
for the reason suggested by the commenter. However, the FAA has revised
the initial compliance time of the final rule to 16 months for the
reasons specified in Item 1. The FAA considers that the extension of
compliance time is justified and will not adversely effect the safety
of the fleet.
Editorial Change to the Proposal
The FAA inadvertently included Boeing Model 737-900 series
airplanes in the applicability of the NPRM. Since that model has not
yet been certificated, the FAA has removed it from the final rule.
Conclusion
After careful review of the available data, including the comments
noted above, the FAA has determined that air safety and the public
interest require the adoption of the rule with the changes previously
described. The FAA has
[[Page 27910]]
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 3,059 Boeing Model 737 series airplanes of
the affected design in the worldwide fleet. The FAA estimates that
1,334 airplanes of U.S. registry will be affected by this AD, that it
will take approximately 1 work hour per airplane to accomplish the
required actions, and that the average labor rate is $60 per work hour.
Based on these figures, the cost impact of the AD on U.S. operators is
estimated to be $80,040, or $60 per airplane, per cycle.
It will take 9 work hours to remove and reinstall or replace the
PCU. For Model 737-100, -200, -300, -400, and -500 series airplanes,
however, concurrent accomplishment of this AD and AD 97-14-04 will
preclude the necessity to accomplish this replacement action twice,
thereby offsetting the cost impact on operators.
The cost impact figure discussed above is based on assumptions that
no operator has yet accomplished any of the requirements of this AD
action, and that no operator would accomplish those actions in the
future if this AD were not adopted.
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:
99-11-05 Boeing: Amendment 39-11175. Docket 98-NM-383-AD.
Applicability: All Model 737 series airplanes, certificated in
any category.
Note 1: This AD applies to each airplane identified in the
preceding applicability provision, regardless of whether it has been
modified, altered, or repaired in the area subject to the
requirements of this AD. For airplanes that have been modified,
altered, or repaired so that the performance of the requirements of
this AD is affected, the owner/operator must request approval for an
alternative method of compliance in accordance with paragraph (e) 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 failure of the secondary servo valve slide in the
rudder power control unit (PCU) due to cracking of the slide, and
consequent rudder hardover and reduced controllability of the
airplane, accomplish the following:
Displacement Testing
(a) Perform a displacement test of the secondary slide in the
dual servo valve in the rudder PCU, in accordance with Boeing Alert
Service Bulletin 737-27A1221, Revision 1, dated January 28, 1999
(for Model 737-100, -200, -300, -400, and -500 series airplanes); or
737-27A1222, Revision 1, dated January 28, 1999 (for Model 737-600,
-700, and -800 series airplanes); at the applicable time specified
by paragraph (a)(1), (a)(2), (a)(3), or (a)(4) of this AD. Repeat
the displacement test on that PCU thereafter at intervals not to
exceed 24,000 flight hours.
Note 2: Accomplishment of the initial displacement testing
required by paragraph (a) of this AD in accordance with Boeing Alert
Service Bulletin 737-27A1221, dated January 14, 1999 (for Model 737-
100, -200, -300, -400, and -500 series airplanes); or 737-27A1222,
dated January 14, 1999 (for Model 737-600, -700, and -800, series
airplanes) is acceptable only for the initial compliance
requirements of this AD.
(1) For Model 737-100, -200, -300, -400, and 500 series
airplanes: Conduct the displacement test within 16 months after the
effective date of this AD.
(2) For airplanes equipped with a PCU having part number 65-
44861-12 and having serial number (S/N) 3509A or lower: Conduct the
displacement test within 16 months after the effective date of this
AD.
(3) For Model 737-600, -700, and -800 series airplanes having
line numbers 1 through 222 inclusive: Conduct the displacement test
within 16 months after the effective date of this AD.
(4) For all other airplanes: Conduct the displacement test prior
to the accumulation of 24,000 total flight hours on the PCU, or
within 30 days after the effective date of this AD, whichever occurs
later.
Corrective Actions
(b) If the results of the displacement test required by
paragraph (a) of this AD are outside the limits specified by Boeing
Alert Service Bulletin 737-27A1221, Revision 1, dated January 28,
1999 (for Model 737-100, -200, -300, -400, and -500 series
airplanes), or 737-27A1222, Revision 1, dated January 28, 1999 (for
Model 737-600, -700, and -800 series airplanes): Prior to further
flight, accomplish the actions specified in paragraphs (b)(1) and
(b)(2) of this AD.
(1) Replace the valve assembly, in accordance with the
applicable alert service bulletin, with a serviceable valve
assembly. And
(2) Following installation of the replacement valve assembly in
accordance with paragraph (b)(1) of this AD, perform the
displacement test required by paragraph (a) of this AD on that
assembly, in accordance with the applicable alert service bulletin.
If the test results are outside the limits specified by the
applicable alert service bulletin, prior to further flight, replace
the valve assembly with a serviceable valve assembly in accordance
with the applicable alert service bulletin, and repeat the
displacement test required by paragraph (a) of this AD on that
assembly.
Note 3: Boeing Alert Service Bulletin 737-27A1222, Revision 1,
dated January 28, 1999, refers to Parker Service Bulletin 381500-27-
01, dated December 22, 1998, as an additional source of service
information for accomplishment of the displacement test for Model
737-600, -700, and -800 series airplanes.
(c) As of 16 months after the effective date of this AD, no
person shall install on any airplane a main rudder PCU having serial
number (S/N) 3509A or lower (for Model 737-100, -200, -300, -400,
and -500 series airplanes) or S/N 0299 or lower (for Model 737-600,
-700, and -800 series airplanes)
[[Page 27911]]
unless that PCU's nameplate has been vibro-engraved with the letter
``C'' or letters greater than ``C'' following the serial number. PCU
nameplates that have been vibro-engraved with the letter ``C'' or
letters greater than ``C'' following the serial number are
considered to be in compliance with the requirements for the initial
inspection of this AD.
(d)(1) Within 30 days after accomplishing the initial
displacement test required by paragraph (a) of this AD: Submit a
report of the testing to the Manager, Seattle Aircraft Certification
Office (ACO), FAA, Transport Airplane Directorate, 1601 Lind Avenue,
SW., Renton, Washington 98055-4056; fax (425) 227-1181. The report
must include the displacement testing results (both positive and
negative findings), test data for any failed valve assemblies, a
description of any discrepancies if found, the part number and
serial number of each rudder PCU tested, and the airplane serial
number.
(d)(2) Within 30 days after accomplishing any repetitive
displacement testing required by paragraph (a) of this AD: Submit a
report of any failed valve assembly to the Manager, Seattle Aircraft
Certification Office (ACO), FAA, Transport Airplane Directorate,
1601 Lind Avenue, SW., Renton, Washington 98055-4056; fax (425) 227-
1181. The report must include the displacement testing results of
any failed valve assembly, test data for any failed valve
assemblies, a description of any discrepancies found, the part
number and serial number of each rudder PCU with a failed valve
assembly, and the airplane serial number.
(d)(3) Within 30 days after accomplishing the initial
displacement test required by paragraph (a) of this AD: Submit
failed valve assemblies for analysis to Parker Hannifin Corporation,
Chief Engineer, Customer Support Operations, 16666 Von Karman
Avenue, Irvine, California 92606.
(d)(4) Information collection requirements contained in this
regulation have been approved by the Office of Management and Budget
(OMB) under the provisions of the Paperwork Reduction Act of 1980
(44 U.S.C. 3501 et seq.) and have been assigned OMB Control Number
2120-0056.
Alternative Methods of Compliance
(e) 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 ACO. 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 4: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Seattle ACO.
Special Flight Permits
(f) 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.
Incorporation by Reference
(g) The actions shall be done in accordance with Boeing Alert
Service Bulletin 737-27A1221, Revision 1, dated January 28, 1999, or
Boeing Alert Service Bulletin 737-27A1222, Revision 1, dated January
28, 1999. 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.
(h) This amendment becomes effective on June 28, 1999.
Issued in Renton, Washington, on May 13, 1999.
D. L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 99-12690 Filed 5-21-99; 8:45 am]
BILLING CODE 4910-13-P
