[Federal Register Volume 59, Number 96 (Thursday, May 19, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-11780]
[[Page Unknown]]
[Federal Register: May 19, 1994]
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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39
[Docket No. 93-NM-151-AD; Amendment 39-8917; AD 94-10-10]
Airworthiness Directives; Boeing Model 747-100, -200, and -300
Series Airplanes Equipped With Pratt & Whitney JT9D Series Engines
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
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SUMMARY: This amendment adopts a new airworthiness directive (AD),
applicable to Boeing Model 747-100, -200, and -300 series airplanes,
that requires modification of the thrust reverser control system by
installing a solenoid-operated shut-off valve. This amendment is
prompted by incidents of deployment of the engine fan thrust reverser
during flight. The actions specified by this AD are intended to prevent
such deployment, which could result in reduced controllability of the
airplane.
DATES: Effective June 20, 1994.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of June 20, 1994.
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: G. Michael Collins, Aerospace
Engineer, Propulsion Branch, ANM-140S, FAA, Transport Airplane
Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue,
SW., Renton, Washington 98055-4056; telephone (206) 227-2689; 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), applicable to Boeing Model 747-100, -200, and -300
series airplanes equipped with Pratt & Whitney JT9D series engines, was
published in the Federal Register on December 7, 1993 (58 FR 64386).
That action proposed to require modification of the thrust reverser
control system by installing a solenoid-operated shut-off valve.
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
One commenter supports the proposal.
Several commenters contend that the proposed modification is not
necessary and the proposed rule should be withdrawn. These commenters
state that the high reliability of both the Thrust Reverser Sequencing
Mechanism (TRSM) and the thrust reverser system preclude the need for
the proposed shut-off valve installation. These commenters note that
the manufacturer's service bulletin referenced in the proposal does not
clearly state that the shut-off valve will prevent an in-flight
deployment of the thrust reversers. The FAA does not concur. The
reliability of the TRSM or the thrust reverser system does not affect
the requirement for the solenoid-operated shut-off valve. An in-flight
deployment of a thrust reverser can occur even with a fully functioning
thrust reverser system with all components (including the TRSM)
operating within maintenance limits, if the pneumatic signal line vent
on the Directional Control Valve (DCV) becomes plugged. The
installation of the shut-off valve prevents this single malfunction
from causing such a deployment.
Further, the design of the thrust reverser control system is such
that there is a constant supply of pneumatic signal air to the DCV.
When the thrust levers are in the ``idle'' or ``forward thrust''
position, air flows through the DCV to the stow port of the gear
switching actuator. Signal air leakage from the stow chamber to the
deploy chamber occurs even with an actuator that is within overhaul
limits. The signal air that leaks into the deploy chamber is designed
to be vented through the actuator deploy port and the deploy signal
line to the DCV, where it exits through the DCV vent. If this vent path
becomes plugged, the pressure in the deploy chamber will rise.
Pressurization of the deploy chamber of the gear switching actuator can
cause the gear switching actuator to move to the ``deploy'' position.
Additionally, drive air is supplied to the thrust reverser
Pneumatic Drive Unit (PDU) through a Pressure Regulator Shut-off Valve
(PRSOV). The PRSOV opens when it receives pneumatic signal air from the
DCV. This signal is received whenever the thrust levers are moved to
the idle position, either in flight or on the ground. If the DCV vent,
deploy signal line, or gear switcher actuator deploy chamber port
becomes plugged and causes the gear switcher actuator to move to the
``deploy'' position, the thrust reverser will deploy when the thrust
lever is moved to the ``idle'' position. Plugging of this vent path has
caused approximately 30 (of 31) known events of in-flight deployment of
the thrust reversers on Model 747 airplanes. Such plugging has been
caused by improper deactivation procedures, pieces of air filter media,
and ice formed during flight.
The installation of the solenoid-operated shut-off valve required
by this AD will prevent the flow of pneumatic drive air to the PDU,
unless the airplane is on the ground and the reverse thrust levers are
in the ``reverse thrust'' position. The shut-off valve is installed
between the PRSOV and the thrust reverser PDU. The shut-off valve opens
only when the airplane air/ground logic is in the ground mode and
``reverse thrust'' is selected. Therefore, the shut-off valve is
designed to prevent in-flight deployment of the thrust reverser by
preventing the flow of drive air to the PDU (unless the airplane is on
the ground and ``reverse thrust'' is selected).
There has been only one reported in-flight deployment of a thrust
reverser on a Model 747 involving an engine that was equipped with the
solenoid-operated shut-off valve. However, this incident was determined
to have been caused by a maintenance crew that disconnected the PDU
drive shafts to the thrust reverser in order to deactivate the thrust
reverser, and inadvertently did not lock the reverser sleeve. By
disconnecting the two drive shafts, the two reverser locking devices
were disconnected. Thus, the improper deactivation of the reverser
contributed to the in-flight deployment incident. By disconnecting the
PDU drive shafts, the pneumatic drive was taken out of the system;
therefore, the shut-off valve had no effect on the deployment.
None of the other 30 incidents of in-flight deployments of the
thrust reversers on Model 747's have occurred on engines equipped with
the subject solenoid-operated shut-off valve. The FAA considers that
all of those events could have been prevented if the shut-off valve had
been installed.
For these reasons, the FAA has determined that installation of the
solenoid-operated shut-off valve is appropriate and warranted.
Several commenters do not support the need for the issuance of the
proposed rule. These commenters state that the Model 747 has been shown
to be controllable following all incidents of in-flight deployment of
the thrust reversers. They contend that these incidents of deployment
occurred at idle thrust, and that the proposed modification would only
help in preventing uncommanded deployments at idle thrust or where
improper lockout of the reverser sleeve had been performed. The FAA
does not concur with these commenters' inference that issuance of the
rule is not necessary. The FAA acknowledges that, in all of the known
events of in-flight thrust reverser deployments, the flight crews were
able to control the airplanes and land safely. At the time this rule
was proposed, there was insufficient data to demonstrate that the
airplane would be controllable in all phases of flight following
deployment of a thrust reverser. Recently, however, Boeing has
presented the results of a study it conducted on the controllability of
the airplane following an in-flight deployment event in several phases
of flight. The results of this study revealed that these airplanes
could experience certain control problems in the event of a thrust
reverser deployment occurring during high speed climb or possibly
during cruise. This additional information on the controllability of
the airplane following deployment of an outboard thrust reverser
further demonstrates the need to install the solenoid-operated shut-off
valve. For example, if the thrust lever is moved rapidly to the
``idle'' position from a high power setting, and the DCV vent is
plugged (e.g., by ice), the thrust reverser could deploy at a high
thrust level as the engine decelerates. The installation of the shut-
off valve is designed to prevent pneumatic drive air from powering the
PDU, unless the airplane is on the ground and ``reverser thrust'' is
selected, thereby preventing in-flight deployments.
Several commenters request that the proposed rule be revised to
allow the accomplishment of certain revised maintenance practices, in
lieu of installation of the shut-off valve. These commenters point out
that the majority of the incidents of in-flight deployments of thrust
reversers have involved improper or outdated maintenance practices
relative to deactivating the reverser. The Model 747 Maintenance Manual
has been revised to delete all deactivating procedures except one,
which involves disconnecting the PDU drive shafts and then ensuring
that the reverser sleeve is locked in the stowed position. The
commenters contend that, with such procedures now deleted from normal
maintenance practices, circumstances that previously would have led to
a deployment incident will now be eliminated. The FAA does not concur.
Although this new maintenance procedure may serve to preclude in-flight
deployments caused by improper deactivating procedures, the FAA finds
that no maintenance procedure can prevent in-flight deployments caused
by blocking of the DCV vent (by ice, foreign objects, etc.).
Additionally, the FAA points out that several revisions had been made
previously to the Model 747 Maintenance Manual in an attempt to prevent
in-flight deployments of the thrust reverser, yet deployments have
continued to occur. As stated elsewhere in this preamble, the FAA
considers that the installation of the subject shut-off valves would
have prevented 30 of the 31 known incidents of in-flight deployments on
Model 747's, since those incidents involved blocking of the DCV vent.
Numerous commenters request that the proposed compliance time of 24
months for modification be extended to between 36 months and 5 years.
Several of these commenters point out that there is a 300- to 400-day
lead time necessary for purchasing and obtaining necessary parts. This
lengthy lead time for parts delivery would seriously hamper affected
operators' ability to comply with the proposed rule within a 24-month
deadline, and would cause major scheduling problems, delays, and flight
cancellations. Other commenters request an extension to in order to
allow the modification to be accomplished during a regularly scheduled
``heavy'' maintenance visit (``D'' check) at a main base, where
required equipment and trained personnel would be available. The FAA
agrees that the compliance time can be extended somewhat. Based on
information provided by the commenters concerning parts availability,
the FAA has determined that a compliance time of 36 months is
appropriate in order to accommodate the time necessary for affected
operators to order, obtain, and install the modification; and will not
compromise safety. The final rule has been revised accordingly.
Certain commenters request that the proposed rule be revised to
permit the installation of unmodified engines after the effective date
of the AD and until the compliance time for modification. These
commenters point out that proposed paragraph (b) would require that, as
of the effective date of the rule, no operator install an unmodified
engine on any airplane. However, to comply with this paragraph,
operators would have to modify all spare engines prior to the effective
date of the AD; this would be impossible, due to the lead time
necessary to obtain parts, and would impose an economic burden on
operators. The FAA concurs. The final rule has been revised to permit
installation of an unmodified engine up to 18 months after the
effective date of the rule. This compliance time of 18 months is based
on a 1-year period that would be necessary to obtain parts, plus a 6-
month period to modify all spare engines.
One commenter requests that the proposed rule be revised to require
the installation of a new PDU to prevent the back driving of the thrust
reverser. This commenter has installed such a unit in accordance with
Boeing Service Bulletins 747-78-2084 and 747-78-2090, and Garrett
Service Bulletins 126712-78-1432 and 126236-78-1332. Since
installation, this commenter has not experienced any in-flight
deployments of the thrust reverser. The commenter recommends this
installation in lieu of the shut-off valve that would be required the
proposed AD. The FAA does not concur. The modification referred to by
the commenter entails the installation of a reversible PDU in place of
the gear-driven PDU that was installed on earlier Model 747 airplanes
equipped with Pratt & Whitney JT9D engines. The pneumatic control
system used with the reversible PDU is similar to the control system
used with the gear-driven PDU. One difference is that a ``directional
switcher actuator'' is used with the reversible PDU, in place of the
``gear switcher actuator'' used with the gear-driven PDU; however, both
actuators are similar in design, and their deploy chamber vent paths
are the same. Therefore, if the DCV vent, deploy signal line, or the
directional switcher actuator deploy chamber port becomes plugged, the
directional switcher actuator could move to the ``deploy'' position. If
this occurs, the thrust reverser will deploy when the thrust lever is
moved to the ``idle'' position, just as is the case for the gear-driven
PDU configuration. Installation of the subject shut-off valve will
prevent this from occurring. In light of this, the FAA has determined
that installation of the shut-off valve is necessary, regardless of the
type of PDU that is installed.
Other commenters request that the proposed rule be revised to allow
alternative approaches, in lieu of the modification, to address the
identified unsafe condition. The commenters state that the cost of the
specific proposed modification is an unnecessary burden on operators,
and consider that improved maintenance procedures are all that are
necessary to ensure safety of the system. For the reasons previously
described in this preamble, the FAA does concur with these commenters'
specific suggestions for ``alternative approaches.'' At this time,
based on all available data to date, the FAA has determined that the
modification required by the AD is the only action that will prevent
in-flight deployments of the thrust reverser caused by blockage of the
DCV vent. No maintenance action or acceptable alternative modification
has yet been presented to the FAA that will prevent a deployment caused
by this single modification. However, under the provisions of paragraph
(c) of the final rule, operators may request approval of the use of
alternative methods of compliance, provided that sufficient data is
presented to the FAA to justify the request.
Numerous commenters request that the economic impact information
presented in the preamble to the notice be revised to provide updated
costs. These commenters state that the costs indicated in the preamble
to the proposed rule were greatly underestimated. The FAA concurs. The
estimated modification costs that were presented in the preamble to the
proposal were based on information provided by the airplane
manufacturer at the time the proposed rule was being developed. The
manufacturer has now provided updated costs for the parts and labor
necessary to modify affected airplanes, and the economic impact
information, below, has been revised accordingly.
The economic impact information has also been revised to update the
current number of airplanes that will be affected by this AD.
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.
There are approximately 221 Model 747-100, -200, and -300 series
airplanes of the affected design in the worldwide fleet. The FAA
estimates that 124 airplanes of U.S. registry will be affected by this
AD, that it will take approximately 128 work hours per airplane to
accomplish the required actions, and that the average labor rate is $55
per work hour. Required parts will cost approximately $75,356 per
airplane. Based on these figures, the total cost impact of the AD on
U.S. operators is estimated to be $10,217,104, or $82,396 per airplane.
The number of required work hours, as indicated above, is presented
as if the accomplishment of the modification required by this AD were
to be conducted as a ``stand alone'' action. However, the 36-month
compliance time specified in paragraph (a) of this AD allows ample time
for the modification to be accomplished coincidentally with scheduled
major airplane inspection and maintenance activities, thereby
minimizing the costs associated with special airplane scheduling.
The total 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.
The FAA recognizes that the obligation to maintain aircraft in an
airworthy condition is vital, but sometimes expensive. Because AD's
require specific actions to address specific unsafe conditions, they
appear to impose costs that would not otherwise be borne by operators.
However, because of the general obligation of operators to maintain
aircraft in an airworthy condition, this appearance is deceptive.
Attributing those costs solely to the issuance of this AD is
unrealistic because, in the interest of maintaining safe aircraft, most
prudent operators would accomplish the required actions even if they
were not required to do so by the AD.
A full cost-benefit analysis has not been accomplished for this AD.
As a matter of law, in order to be airworthy, an aircraft must conform
to its type design and be in a condition for safe operation. The type
design is approved only after the FAA makes a determination that it
complies with all applicable airworthiness requirements. In adopting
and maintaining those requirements, the FAA has already made the
determination that they establish a level of safety that is cost-
beneficial. When the FAA, as in this AD, makes a finding of an unsafe
condition, this means that this cost-beneficial level of safety is no
longer being achieved and that the required actions are necessary to
restore that level of safety. Because this level of safety has already
been determined to be cost-beneficial, a full cost-benefit analysis for
this AD would be redundant and unnecessary.
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 14 CFR part
39 of the Federal Aviation Regulations as follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C.
106(g); and 14 CFR 11.89.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new
airworthiness directive:
94-10-10 Boeing: Amendment 39-8917. Docket 93-NM-151-AD.
Applicability: Model 747-100, -200, and -300 series airplanes;
equipped with Pratt & Whitney JT9D series engines; certificated in
any category.
Compliance: Required as indicated, unless accomplished
previously.
To prevent inadvertent engine fan thrust reverser deployment
during flight, which could result in reduced controllability of the
airplane, accomplish the following:
(a) Within 36 months after the effective date of this AD, modify
the thrust reverser control system to include a solenoid-operated
shut-off valve in accordance with Boeing Service Bulletin 747-78-
2052, Revision 4, dated March 23, 1989.
Note: Airplanes on which the modification has been accomplished
previously in accordance with Boeing Service Bulletin 747-78-2052,
Revision 3, dated August 27, 1987, are considered to be in
compliance with this paragraph.
(b) As of 18 months after the effective date of this AD, no
person shall install a Pratt & Whitney JT9D series engine on any
airplane unless the thrust reverser control system installed on that
engine has been modified to include a solenoid-operated shut-off
valve in accordance with Boeing Service Bulletin 747-78-2052,
Revision 4, dated March 23, 1989.
(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: 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
Secs. 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 modification shall be done in accordance with Boeing
Service Bulletin 747-78-2052, Revision 4, dated March 23, 1989,
which contains the following list of effective pages:
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Revision level
Page No. shown on page Date shown on page
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1-5, 12-13,-19-21, 35, 38, 46 4 March 23, 1989.
6-7, 18, 39, 41.............. 3 August 27, 1987.
15, 23-24, 36, 42-45, 47-49 2 January 9, 1976.
30-31, 40.
10, 16, 22, 37............... 1 March 28, 1975.
8-9, 11, 14, 17, 25-29, 32-34 Original July 19, 1974.
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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.
(f) This amendment becomes effective on June 20, 1994.
Issued in Renton, Washington, on May 10, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 94-11780 Filed 5-18-94; 8:45 am]
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