[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