[Federal Register Volume 61, Number 216 (Wednesday, November 6, 1996)]
[Rules and Regulations]
[Pages 57291-57295]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-26952]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
RIN 2120-AA64
[Docket No. 94-NM-226-AD; Amendment 39-9790; AD 96-22-01]
Airworthiness Directives; Boeing Model 747-200, -300, and -400
Series Airplanes
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
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SUMMARY: This amendment adopts a new airworthiness directive (AD),
applicable to certain Boeing Model 747-200, -300, and -400 series
airplanes, that requires modification of the left and right inboard
elevator servo assemblies and the hydraulic routing of the right
inboard elevator power control package (PCP). This amendment is
prompted by a report of an uncommanded right elevator deflection after
takeoff and reports of elevator/control column bumps during landing
gear retraction on these airplanes. The actions specified by this AD
are intended to prevent uncommanded elevator deflection, which could
result in structural damage and reduced controllability of the
airplane.
DATES: Effective December 6, 1996.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of December 6, 1996.
ADDRESSES: The service information referenced in this AD may be
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle,
Washington 98124-2207; and Parker Hannifin Corporation, Customer
Support Operations, 16666 Von Karman Avenue, Irvine, California 92714.
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: Kristin Larson, 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 (206) 227-1760; fax (206)
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 certain Boeing Model 747 series
airplanes was published as a supplemental Notice of Proposed Rulemaking
(NPRM) in the Federal Register on December 11, 1995 (60 FR 63465). That
action proposed to require modification of the left and right inboard
elevator servo assemblies and the hydraulic routing of the right
inboard elevator power control package (PCP).
Comments
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
Requests To Extend the Compliance Time for Hydraulic Tubing
Modification
Two commenters request that the compliance time for accomplishing
the proposed modification of the hydraulic tubing of the right inboard
elevator PCP be extended from the proposed 1 year to 18 months. The
commenters state that such an extension will allow the modification to
be accomplished during a regularly scheduled ``C'' or ``D'' check, and
thereby eliminate any additional expenses that would be associated with
special scheduling.
One of these commenters notes that it had submitted an identical
request to the FAA during the comment period for the original NPRM, but
the FAA denied this request, in part, because it ``determined that a
heavy maintenance visit is not required to accomplish the
modification.'' The commenter states that the proposed modification
requires draining and purging of the stabilizer fuel tank, which is not
an activity suited for a line or field maintenance environment.
Additionally, access to remove the elevator actuator and modify the
hydraulic tubing on the stabilizer aft spar would be difficult to
accomplish during line maintenance or at a field maintenance facility.
[[Page 57292]]
The FAA does not concur with the commenters' request to extend the
compliance time. The FAA agrees that, due to the complexity of the
modification, it should be performed at a facility where special
equipment and trained maintenance personnel will be available, if
necessary. However, the FAA points out that the compliance time of one
year was developed in consideration of not only the degree of urgency
associated with addressing the unsafe condition, but such factors as
the manufacturer's recommendations, the availability of required parts,
and the practical aspect of installing the required modification within
an interval of time that parallels normal scheduled maintenance for the
majority of affected operators. In consideration of all of these
factors, and in consideration of the amount of time that has already
elapsed since issuance of the original NPRM, the FAA has determined
that further delay of this modification is not appropriate.
However, under the provisions of paragraph (c) of the final rule,
the FAA may approve requests for adjustments to the compliance time if
sufficient data are submitted to substantiate that such an adjustment
would provide an acceptable level of safety.
Requests To Extend the Compliance Time for Servo Assembly
Modification
Several commenters request that the compliance time for
accomplishing the proposed modification of the left and right servo
assemblies of the inboard elevator PCP be extended from the proposed 3
years to 5 years or, preferably, to 7 years. Some of these commenters
contend that, due to the complexity and proprietary technology used to
manufacture the servo valve, Parker (the original equipment
manufacturer/supplier of the assemblies) is the only facility that is
qualified to perform the rework and retrofit that would be required by
the proposed modification. These commenters state that Parker's current
facility would be unable to support modification of the affected fleet
within the proposed 3-year compliance time; therefore, additional time
will be necessary for compliance. One commenter contends that, even if
other maintenance facilities are available to accomplish the
modification, a sufficient inventory of parts to support multiple
repair facilities does not currently exist.
The FAA does not concur. In developing an appropriate compliance
time for this modification, the FAA specifically considered the
availability of required parts as well as the process necessary for
modifying the affected fleet in an orderly and timely manner. The FAA
maintains that other facilities will be able to support maintenance of
the PCP's, even if the spool valve units must be modified only by
Parker. In consideration of all of these items (as well as the revision
to the applicability of this requirement, as explained below), the FAA
finds that a compliance time of 3 years for this modification is
appropriate. However, under the provisions of paragraph (c) of the
final rule, the FAA may approve requests for adjustment of the
compliance time if sufficient data are submitted to substantiate that
such an adjustment would provide an acceptable level of safety.
Requests To Reconsider Limiting the Applicability of Servo Assembly
Modification
Several commenters request that the applicability of proposed
paragraph (b) (which would require the modification of the left and
right servo assemblies of the inboard elevator PCP) be limited to only
Model 747-200 and -300 series airplanes having cumulative line number
(C/L) 696 and subsequent. These commenters request that airplanes
having C/L 001 through 695 (which are commonly referred to as
``classic'' models) and Model 747-400 series airplanes, be exempt from
this requirement. These commenters bring up three reasons to justify
this request.
1. No history of service actuator assembly failures on ``classic''
models. Several commenters state that the servo assembly modification
is unjustified for ``classic'' model airplanes because the entire Model
747 fleet has accumulated over 87 million flight hours, during which
time, there have been no reports of uncommanded elevator movement on
the ``classic'' model airplanes. These commenters point out that they
submitted an identical request to the FAA during the comment period for
the original NPRM, but, again, the FAA denied the request. As part of
the reason for its denial, the FAA indicated that only a small
percentage of airplanes are equipped with a flight data recorder that
records the position of the elevator; therefore, if an operator elects
to record only the control column position and an uncommanded elevator
motion occurred, the incident may not be recorded, due to the flight
crew's inability to confirm the anomaly. However, several of the
commenters point out the flight crew can quickly ascertain the cause of
a sudden pitching moment, since the elevator position is indicated on
the flight deck for the flightcrew to see. Another commenter states
that, even if operators have elected not to record the control surface
position, it still does not negate the fact that there have been over
87 million flight hours of safe flight of the Model 747 fleet on which
the proposed modification has not been installed. Therefore, the
commenters request that, when determining whether the current servo
configuration is safe, the FAA should also consider this long history
of absence of reports of uncommanded elevator motion.
2. Potential structural damage concerns on Model 747-100, -100B
SUD, -200, -300, SR, and SP series airplanes up to and including C/L
695. One commenter points out that it submitted a similar request,
along with a justifying probability analysis, to the original NPRM.
That analysis was conducted to demonstrate that the aft fuselage
structural limit load cannot be exceeded for the ``classic'' model
airplanes for any valve jam in any portion of the flight envelope. As a
result of that analysis, the commenter states that the probability of
exceeding the structural limit of the aft fuselage on these airplanes
is less than 1 x 10-9. The FAA did not concur with that request,
and indicated that the analysis was based ``on a sampling that was much
too small from which accurate statistical conclusions could be drawn
that would be representative of the fleet.'' The commenter states that
this FAA statement and others in the Discussion section of the preamble
to the supplemental NPRM indicate that clarification is necessary. The
commenter notes that the structural and systems configurations of
``classic'' model airplanes are such that, the maximum capability of
the hydraulic system cannot induce a valve pressure on that airplane
that exceeds structural limit loading; this point does not rely on the
statistical sampling presented for the net valve differential pressure.
The commenter maintains that the key point of the analysis it submitted
previously is that only Model 747-200 and -300 series airplanes having
C/L 696 and subsequent require the retrofit for potential structural
damage concerns.
3. Hydraulic tube change eliminates the possibility of high
pressure spike for Model 747-400 series airplanes. Several commenters
request that Model 747-400 series airplanes be removed from the
applicability of proposed paragraph (b) and not be subject to the servo
modification requirement. One commenter states that a high pressure
spike in hydraulic system 4 was identified as the source of the valve
movement that caused the initial incident on which this AD action is
based; the commenter maintains that the
[[Page 57293]]
hydraulic tubing modification required by proposed paragraph (a) of the
AD will remove the possibility of such high pressure spikes. Therefore,
the servo assembly modification would be unnecessary. Two commenters
present test results and analyses defending this position.
Certain commenters submitted a similar request, along with analysis
of data, to the original NPRM, but note that the FAA denied it. As
reason for its denial, the FAA concluded that the data submitted ``do
not substantiate * * * that routing the hydraulic system 3 to the
sensitive side of the servo valve would preclude uncommanded elevator
deflection.'' One of the commenters believes that the FAA drew these
conclusions based on hydraulic pressure data for only one Model 747-400
airplane; the commenter contends that such data are too small for the
FAA to draw accurate conclusions. In light of this, the commenters
request that the proposed modification of the servo assembly be deleted
until the FAA conducts further studies of hydraulic systems 3 and 4
pressure fluctuations on affected airplanes.
The FAA has reconsidered its previous position and partially
concurs with the commenters' request. However, a clarification of
certain points associated with the data that were submitted by these
commenters in support of their initial request must first be addressed.
As for Item 1, indicated above, the FAA has considered the absence
of reports of uncommanded elevator motion, as brought up by these
commenters. The FAA finds that an absence of reports may be due to the
fact that a flight data recorder is not installed on all airplanes that
records the elevator surface movement. However, the FAA agrees with the
commenters that the recording of the elevator time history is not the
sole determination in the reporting of an event. The FAA also agrees
with the commenters that the occurrence of uncommanded elevator
movement would most likely be quickly ascertained by the flight crew.
However, the FAA still maintains that the ability to confirm the
anomaly may not exist.
As for Item 2, indicated above, the FAA has re-reviewed the
probability analysis that Boeing submitted. Based on Boeing's
clarification of the previously submitted data, the FAA has determined
that the ``classic'' model airplanes should not be subject to the
modification of the servo assembly. The FAA has determined that the
``classic'' model airplanes have sufficient structural strength to
sustain a potential valve jam in the elevator PCP. Based on the
configuration and loading of the ``classic'' model airplanes, the limit
load cannot be exceeded with this type of valve jam. While the
possibility of degradation in the controllability of these airplanes
still exists, it is extremely improbable.
In addition, the FAA has determined that Model 747-200 and -300
series airplanes having C/L 696 and subsequent, are subject to the
requirements of paragraph (b) of the AD. The FAA bases this
determination on the fact that the limit load capability of the Model
747-200 and -300 series airplanes having C/L 696 and subsequent,
commonly referred to as ``common tail classic'' model airplanes, is
similar to that of the ``classic'' model airplanes, but have a similar
control configuration as that of Model 747-400 series airplanes. Due to
the changes made in the configuration of the ``common tail classic''
model airplanes, uncommanded elevator motion could cause structural
loading on these airplanes, which could result in structural damage and
reduced controllability of the airplane.
As for Item 3, indicated above, Boeing has conducted further
testing, since issuance of the supplemental NPRM. The FAA has reviewed
the results of this testing. The FAA has determined that the data
presented do not adequately support that the high pressure spike in the
hydraulic system 4 is the only potential cause of a secondary slide
jam; or a pressure fluctuation will not occur in the hydraulic system
3, which could lead to a potential uncommanded valve movement.
In addition, the FAA has re-reviewed the data submitted by the
commenters and maintains that:
The analysis is based on a sampling size that is too small
from which accurate statistical conclusions can be drawn that would be
representative of the fleet.
The variability in the data and the tests for normality
indicate that the data depart from the mean.
Due to the sampling size of the data, a strong argument
supporting normality cannot be inferred.
The flow rate and differential pressures used by the
commenters in the analysis were not substantiated to be the worst case
scenario.
Uncommanded elevator motion may occur on all Model 747
series airplanes if the servo valve secondary slide moves to the
valve's internal stop, regardless of hydraulic system routing.
Therefore, the FAA finds that accomplishment of the hydraulic
tubing modification alone, as required by paragraph (a) of the AD, does
not adequately eliminate the possibility of crossflow in the servo
valve on Model 747-400 series airplanes. The FAA acknowledges the
possibility that uncommanded valve motion may be reduced following the
installation of the hydraulic tubing modification on Model 747-400
series airplanes. However, the FAA finds that the data presented, as
well as service history, do not adequately demonstrate that uncommanded
motion is the only potential cause of a secondary slide jam, or that a
pressure fluctuation will not occur in hydraulic system 3 and lead to
uncommanded movement of the valves.
In light of the all of factors discussed above and the review of
all of the data submitted, the FAA has determined that the servo
assembly modification is warranted only for:
1. Model 747-200 and -300 series airplanes having C/L 696 and
subsequent (the ``common tail classic'' model airplanes) and
2. The Model 747-400 series airplanes.
The applicability of the final rule and of paragraph (b) have been
revised accordingly.
In addition, the FAA has revised the cost impact information,
below, to indicate that the number of airplanes affected by this final
rule has been reduced.
Request To Require Only Certain Type of Testing
One commenter requests that paragraph (b) of the proposed AD be
revised to require that the servo valve be tested only for the
crossflow neutralization improvement feature in accordance with Parker
Service Bulletins 93600-27-173 and 327400-27-171. The commenter states
that certain specific tests that are called out in the service
bulletins, such as the PCU dielectric test and eight-hour duty cycle
test, are unrelated to the subject of the crossflow neutralization
improvement. The commenter considers that revising the proposal as
requested will eliminate redundant and unnecessary testing when
reworking the PCP. The commenter contends that accomplishment of many
of the tests in accordance with the subject service bulletins will not
appreciably affect the flightworthy status of the PCP, as related to
the crossflow enhancement, but will appreciably increase the cost of
performing maintenance on the PCP. The commenter also requests that FAA
allow operators to test the main manifold and assembled PCP's in
[[Page 57294]]
accordance with existing approved procedures.
The FAA does not concur with the commenter's requests. The FAA has
reviewed and approved all of the procedures specified in the Parker
service bulletins that are referenced in paragraph (b) of the AD as the
appropriate source of service information. The FAA has determined that
accomplishment of the modification, including the various follow-on
testing, in accordance with these service bulletins will prevent
blockage of the hydraulic balance passageway by the spring guide, which
can contribute to the uncommanded motion of the PCP. The FAA points out
that some of the tests identified in the subject service bulletins are
optional.
Requests To Revise the Cost Impact Statement
Several commenters question the FAA's cost estimate presented in
the preamble to the supplemental NPRM. These commenters consider the
cost estimate to be significantly understated. Some commenters point
out that the cost of a serviceable elevator PCP will be far greater
than the FAA's estimated cost of $5,910 per unit. One of these
commenters states that a serviceable elevator PCP costs $23,633;
another commenter states that the cost is closer to $45,500.
Additionally, some of the commenters note that, since many of the
affected inboard elevator PCP's are older units, they may need
additional rework or overhaul if they do not pass their respective
acceptance tests. However, the FAA's cost estimate did not take these
costs into consideration. In addition, one of these commenters states
that the FAA's estimates failed to address the cost to modify spare
units.
The FAA finds that clarification of the costs associated with the
requirements of this AD is necessary. The FAA points out that the
economic analysis of the AD is usually limited only to the cost of
actions actually required by the rule. It does not consider the costs
of ``on condition'' actions (e.g., ``repair if a unit fails the
functional test''), 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.
The AD's cost estimate also does not consider the costs of ``spare
parts,'' since part 39 (``Airworthiness Directives'') of the Federal
Aviation Regulations (14 CFR part 39) does not permit AD's to address
parts or components that are not installed on an airplane (``a
product''). Therefore, the FAA cannot require via an AD that operators
modify a ``spare part;'' an AD can only require that the part be
modified before it is installed on an affected airplane.
In addition, the FAA points out that many operators have their own
shop facilities in which to disassemble the PCP and accomplish the PCP
overhaul/modification; for these operators, the costs associated with
those actions may be far less than estimated by the FAA.
As for the exact cost of required parts, the FAA has verified with
the manufacturer that the parts costs that was presented in the cost
impact information in the preamble to the supplemental NPRM, and
reiterated below, are valid.
FAA's Conclusions
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 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 30 Model 747-200 and -300 series airplanes;
and 332 Model 747-400 series airplanes; of the affected design in the
worldwide fleet (362 airplanes total).
There currently are no Boeing Model 747-200 and -300 series
airplanes on the U.S. Register that are subject to the requirements of
this AD. All of the affected airplanes of those models that are
included in the applicability of this rule currently are operated by
non-U.S. operators under foreign registry; therefore, they are not
directly affected by this AD action. However, the FAA considers that
inclusion of these airplanes in the rule is necessary to ensure that
the unsafe condition is addressed in the event that any of these
airplanes are imported and placed on the U.S. Register in the future.
Should any affected Model 747-200 and -300 series airplanes be
imported and placed on the U.S. Register in the future, it would take
approximately 73 work hours per airplane to accomplish the required
modification, at an average labor rate of $60 per work hour. Required
parts will cost approximately $7,440 per airplane. Based on these
figures, the cost impact of the modification required by this AD on
U.S. operators is estimated to be $11,820 per airplane.
The FAA estimates that 65 Model 747-400 series airplanes of U.S.
registry will be affected by this AD, that it will take approximately
111 work hours per airplane to accomplish the required actions, and
that the average labor rate is $60 per work hour. Required parts will
cost approximately $12,269 per airplane. Based on these figures, the
cost impact of the AD on U.S. operators of Model 747-400 series
airplanes is estimated to be $1,230,385, or $18,929 per airplane.
The cost impact figures discussed above are based on assumptions
that no operator has yet accomplished any of the requirements of this
AD action, and that no operator would accomplish those actions in the
future if this AD were not adopted.
Regulatory Impact
The regulations adopted herein will not have substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government. Therefore, in
accordance with Executive Order 12612, it is determined that this final
rule does not have sufficient federalism implications to warrant the
preparation of a Federalism Assessment.
For the reasons discussed above, I certify that this action (1) is
not a ``significant regulatory action'' under Executive Order 12866;
(2) is not a ``significant rule'' under DOT Regulatory Policies and
Procedures (44 FR 11034, February 26, 1979); and (3) will not have a
significant economic impact, positive or negative, on a substantial
number of small entities under the criteria of the Regulatory
Flexibility Act. A final evaluation has been prepared for this action
and it is contained in the Rules Docket. A copy of it may be obtained
from the Rules Docket at the location provided under the caption
ADDRESSES.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.
Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the
Administrator, the Federal Aviation Administration amends part 39 of
the Federal Aviation Regulations (14 CFR part 39) as follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
[[Page 57295]]
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:
96-22-01 Boeing: Amendment 39-9790. Docket 94-NM-226-AD.
Applicability: Model 747-200, -300, and -400 series airplanes
having cumulative line number (C/L) 696 through 1057, inclusive;
equipped with Parker inboard elevator power control packages (PCP)
having part numbers (P/N) 93600-5005 through -5051 inclusive, or P/
N's 327400-1001, -1003, -1005, and -1007; certificated in any
category.
Note 1: This AD applies to each airplane identified in the
preceding applicability provision, regardless of whether it has been
otherwise 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 (c) 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 uncommanded elevator deflection, which could result
in structural damage and reduced controllability of the airplane,
accomplish the following:
(a) For Model 747-400 series airplanes, as listed in Boeing
Alert Service Bulletin 747-27A2348, Revision 1, dated January 26,
1995: Within 1 year after the effective date of this AD, modify the
hydraulic tubing of the right inboard elevator PCP, in accordance
with Boeing Alert Service Bulletin 747-27A2348, Revision 1, dated
January 26, 1995.
(b) For all airplanes: Within 3 years after the effective date
of this AD, modify the left and right servo assemblies of the
inboard elevator PCP, in accordance with Parker Service Bulletin
327400-27-171, Revision 1, dated April 14, 1995, or Parker Service
Bulletin 93600-27-173, dated May 17, 1995, as applicable.
(c) An alternative method of compliance or adjustment of the
compliance time that provides an acceptable level of safety may be
used if approved by the Manager, Seattle Aircraft Certification
Office (ACO), FAA, Transport Airplane Directorate. Operators shall
submit their requests through an appropriate FAA Principal
Maintenance Inspector, who may add comments and then send it to the
Manager, Seattle ACO.
Note 2: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Seattle ACO.
(d) 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.
(e) The modifications shall be done in accordance with Boeing
Alert Service Bulletin 747-27A2348, Revision 1, dated January 26,
1995; Parker Service Bulletin 327400-27-171, Revision 1, dated April
14, 1995; and Parker Service Bulletin 93600-27-173, dated May 17,
1995; as applicable. This incorporation by reference was approved by
the Director of the Federal Register in accordance with 5 U.S.C.
552(a) and 1 CFR part 51. Copies may be obtained from Boeing
Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-
2207; and Parker Hannifin Corporation, Customer Support Operations,
16666 Von Karman Avenue, Irvine, California 92714. 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.
(f) This amendment becomes effective on December 6, 1996.
Issued in Renton, Washington, on October 15, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 96-26952 Filed 11-5-96; 8:45 am]
BILLING CODE 4910-13-U
