[Federal Register Volume 59, Number 24 (Friday, February 4, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-2561]
[[Page Unknown]]
[Federal Register: February 4, 1994]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 33
[Docket No. 93-ANE-14; Notice No. 33-ANE-01]
Special Conditions; Soloy Dual Pac, Inc., Model Soloy Dual Pac
Engine
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed special conditions.
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SUMMARY: This notice proposes special conditions for the Soloy Dual Pac
engine. This engine will have a novel design feature associated with
its configuration. The Dual Pac engine is a propulsion system in which
two Pratt & Whitney (P&W) PT6 gas turbine engines are combined through
a common gearbox to drive a single output propeller shaft. The Dual Pac
engine is intended to provide a degree of continuous operation
following the failure of one of the P&W PT6 engines. The applicable
regulations do not contain adequate or appropriate safety standards for
such a configuration. This notice proposes the additional safety
standards which the Administrator considers necessary to establish a
level of safety equivalent to that established by the airworthiness
standards of part 33 of the Federal Aviation Regulations (FAR).
DATES: Comments must be submitted on or before March 21, 1994.
ADDRESSES: Comments on this proposal may be submitted in triplicate to:
Federal Aviation Administration (FAA), New England Region, Office of
the Assistant Chief Counsel, Attn: Rules Docket No. 93-ANE-14, 12 New
England Executive Park, Burlington, Massachusetts 01803-5299. Comments
must be marked: Docket No. 93-ANE-14. Comments may be inspected at this
location between 8 a.m. and 4:30 p.m., Monday through Friday, except
Federal holidays.
FOR FURTHER INFORMATION CONTACT:
Hania Younis, Seattle Aircraft Certification Office, Propulsion Branch,
ANM-140S, FAA, Northwest Mountain Region, 1601 Lind Avenue SW., Renton,
Washington 98055-4056, telephone (206) 227-2764; fax (206) 227-1181.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested persons are invited to participate in the making of the
proposed special conditions by submitting such written data, views, or
arguments as they may desire. Communications should identify the Rules
Docket number and be submitted in triplicate to the address specified
under ``ADDRESSES.'' All communications received on or before the
closing date for comments, specified under ``DATES,'' will be
considered by the Administrator before taking action on the proposal.
The proposal contained in this notice may be changed in light of the
comments received.
Comments are specifically invited on the overall regulatory,
economic, environmental, and energy aspects of the proposed special
conditions. All comments submitted will be available in the Rules
Docket for examination by interested persons, both before and after the
closing date for comments. A report summarizing each substantive public
contact with FAA personnel concerning this proposal will be filed in
the docket.
Commenters wishing the FAA to acknowledge receipt of their comments
submitted in response to this notice must submit with those comments a
self-addressed, stamped postcard on which the following statement is
made: ``Comments to Docket No. 93-ANE-14.'' The postcard will be date
stamped and returned to the commenter.
Background
General
On November 9, 1990, Soloy Dual Pac, Inc., applied for a
supplemental type certificate for the Dual Pac engine. The Dual Pac
engine is a propulsion concept in which two Pratt & Whitney PT6
engines, currently approved under Type Certificate No. E4EA, drive a
single propeller shaft through a combining gearbox. The Dual Pac engine
incorporates redundant freewheeling, drive, governing, and lubricating
systems. A system of one-way clutches both prevents the propeller shaft
from driving the engine input shafts and allows either engine to drive
the propeller should the other engine fail. The supplemental type
certificate for the Dual Pac engine is to be based on the type
certificate of the Pratt & Whitney PT6 engine.
Safety Analysis
The certification basis of the P&W PT6 engine was established
before the introduction of FAR Sec. 33.75 (Safety Analysis). Section
33.75 addresses four types of engine failure conditions which are
particularly hazardous to the safety of the aircraft. The objective of
Sec. 33.75 is to require an analysis to be performed at the engine
level which establishes that any probable single or multiple failure,
or any probable improper operation will not cause the engine to catch
fire, burst, generate loads greater than the ultimate loads for the
engine mount, or lose the capability to shut down. Consequently, it is
considered appropriate to add a safety analysis requirement to the Dual
Pac engine program.
Also, one objective of the Dual Pac engine is to provide continued
operation after the failure of one P&W PT6 engine. While the safety
analysis regulations of Sec. 33.75 are more extensive than those of the
P&W PT6 engine certification basis, they still do not address this
special ``continue to run'' objective.
Therefore, in light of the above, it is proposed that a safety
analysis requirement, modelled after Sec. 33.75 and expanded to address
continued operation after a single engine failure, be included in the
Dual Pac engine certification basis.
Uncontained Engine Failure
It is assumed that the Dual Pac engine is intended for use in an
aircraft and will be part of an aircraft certification program in the
future. Minimizing the hazards to the aircraft from uncontained engine
debris will be a very important requirement in any such certification
program. In addition, for a design such as the Dual Pac, many design
features intended to minimize such hazards would be determined at the
engine design stage. Therefore, this issue should be addressed
initially during the Dual Pac engine certification program, and
possibly readdressed during the aircraft installation certification
program.
As stated above, one objective of a Dual Pac engine-equipped
aircraft could be continued safe flight and landing after the failure
of one P&W PT6 engine. In order for the Dual Pac engine to achieve this
objective, it must continue to produce adequate and controllable torque
after such a failure. Service experience, however, shows that
uncontained engine failures can result in high velocity fragment
penetration of, among other things, other engines. This could render
the other engine inoperative as well. In the case of the Dual Pac
engine, such an event could end all torque production. Therefore, the
Dual Pac engine must demonstrate that the two P&W PT6 engines should be
protected from each other in order to minimize the hazards associated
with this event.
Gearbox Design, Functioning, and Endurance Testing
Power transmission systems, such as gearboxes, have not been
specifically addressed by engine certification regulations. Previously,
engines incorporating gearboxes, such as fan reduction gearing or
accessor gearboxes, have been evaluated during the course of engine
block tests and other engine certification activities. Transmissions
such as those used in rotorcraft, however, have been addressed in rotor
drive criteria contained in rotorcraft certification regulations. Since
the Dual Pac engine propulsion drive system is part of the engine, it
is proposed that the changes to FAR part 23, which were published as a
Notice of proposed rulemaking (NPRM), ``Small Airplane Airworthiness
Review Program Notice No. 3,'' in the Federal Register on October 3,
1990, (55 FR 40598); and FAR Sec. 33.87 (amended through Amendment 33-
3), be used as a basis for special conditions intended to establish
standards to address the design, function, and endurance testing of the
gearbox. Section 33.87 regulations have been included in order to
establish a comprehensive standard to address the turbine interface
with the gearbox.
Type Certification Basis
Under the provisions of Sec. 21.101 of the FAR, Soloy Dual Pace
Dual Pac, Inc., must show that the Dual Pac engine meets the applicable
provisions of the regulations incorporated by reference in Type
Certificate No. E4EA, or the requirements of the applicable regulations
in effect on the date of the application. The regulations incorporated
by reference in the type certificate are commonly referred to as the
``original type certification basis.''
The regulations incorporated by reference in Type Certificate No.
E4EA are as follows:
(a) FAR Sec. 21.29, Issue of type certificate: import products.
(b) Civil Air Regulations (CAR) Part 10, Certification and Approval
of Import Aircraft and Related Products, March 28, 1955.
(c) FAR Part 33, Airworthiness Standards: Aircraft Engines,
February 1, 1965, as amended through Amendment 33-5.
If the regulations incorporated by reference do not provide
adequate standards with respect to the change, the applicant must
comply with the regulations in effect on the date of application for
the change that the FAA finds necessary to provide a level of safety
equal to that established by the regulations incorporated by reference.
Due to the potential applications of the Soloy Dual Pac engine, the FAA
has determined that it must also be shown to comply with FAR part 33,
dated February 1, 1965, as amended, plus the following sections:
(a) Section 33.7, Amendment 33-12, Engine ratings and operating
limitations.
(b) Section 33.67, Amendment 33-10, Fuel system.
(c) Section 33.68, Amendment 33-10, Induction system icing.
(d) Section 33.96, Amendment 33-11, Engine test in auxiliary power
unit mode.
(e) Section 21.115(a), Applicable requirements.
In addition, compliance must be shown with FAR part 34 (Fuel
Venting and Exhaust Emission Requirements for Turbine Engine Powered
Airplanes); these special conditions contained herein on Safety
analysis, Gearbox design, functioning, and endurance testing, and
Uncontained engine failure; as well as any applicable equivalent safety
findings and any applicable exemptions.
The Administrator finds that the applicable airworthiness
regulations in part 33, as amended, do not contain adequate or
appropriate safety standards for the Soloy Dual Pac engine because of
its novel or unsual design feature. Therefore, the Administrator
proposes special conditions under the provisions of Sec. 21.16 to
establish a level of safety equivalent to that established in the
regulations.
Special conditions, as appropriate, are issued in accordance with
Sec. 11.49 of the FAR after public notice and opportunity for comment,
as required by Secs. 11.28 and 11.29(b), and become part of the type
certification basis in accordance with Sec. 21.101(b)(2).
Conclusion
This proposed action affects only certain novel or unusual design
features on one model engine. It is not a rule of general
applicability, and it affects only the manufacturer who applied to the
FAA for approval of these features on the engine.
List of Subjects in 14 CFR Part 33
Air transportation, Aircraft, Aviation safety, Safety.
The authority citations for these special conditions continues to
read as follows:
Authority: 49 U.S.C. App. 1354(a), 1421, 1423; 49 U.S.C. 106(g);
and 14 CFR 11.49 and 21.16.
The Proposed Special Conditions
Accordingly, the Federal Aviation Administration (FAA) proposes the
following special conditions as part of the type certification basis
for the Soloy Dual Pac, Inc., Model Soloy Dual Pac engine:
(a) Safety Analysis
It must be shown by analysis that any probable malfunction, or any
probable single or multiple failure, or any probable improper operation
of the Dual Pac engine will not cause the Dual Pac engine to--
(1) Catch fire;
(2) Burst (release hazardous fragments through the engine case);
(3) Generate loads greater than those ultimate loads specified in
Sec. 33.23(a);
(4) Lose the capability of being shut down; or
(5) Lose the capability of providing controllable 50 percent of
rated power.
(b) Uncontained Engine Failure
Design precautions must be taken to minimize the damage to one P&W
PT6 engine, in the event of uncontained engine failure of the other P&W
PT6 engine, in order for the unfailed engine to be capable of continued
torque production after such a failure.
(c) Gearbox Design, Functioning, and Endurance Testing
(1) Propulsion Drive System Design. Propulsion drive systems, as
defined in paragraph (c)(1)(i), must meet the requirements as set forth
in paragraphs (c) (1) through (6).
(i) The propulsion drive system includes all parts necessary to
transmit power from the engines to the propeller shaft. This includes
couplings, universal joints, drive shafts, supporting hearings for
shafts, brake assemblies, clutches, gearboxes, transmissions, any
attached accessory pad or drives, and any cooling fans that are
attached to, or mounted on, the propulsion drive system.
(ii) Each propulsion drive system, powered by more than one engine,
must be arranged so that the propeller shaft and its control will
continue to be powered by the remaining engine(s) if any engine fails.
(iii) Each multiengined propulsion drive system must incorporate a
device to automatically disengage any engine from the propeller shaft,
it that engine fails.
(iv) The oil for components of the propulsion drive system that
require continuous lubrication must be sufficiently independent of the
lubrication systems of the engine(s) to ensure operation with any
engine inoperative. The propulsion drive system must be able to operate
at zero oil pressure and 100 percent output speed for at least 15
seconds without damage to the components and without seizure.
(v) Torque limiting means must be provided on all accessory drives
that are located on the propulsion drive system, in order to prevent
the torque limits established for those drives from being exceeded.
(vi) There must be means to provide continued propulsion system
control and operation, following the failure of an engine to
transmission drive shaft.
(vii) In addition to the propulsion drive system complying with the
requirements of paragraph (c)(1)(iii), the propulsion drive system,
powered by more than one engine, must be designed so that torque to the
propeller shaft is not interrupted after failure of any engine or
element in the propeller shaft drive system; and examined in detail to
determine all components and their failure modes that would be vital to
continued control and operation of the propulsion drive system.
(viii) For each component and its failure modes identified by this
examination, it must be shown by appropriate test that such a failure
is not likely to occur in the system component's service life
established by these tests; or that the system is designed so continued
control and operation can be accomplished after occurrence of the
failure.
(2) Propulsion Drive System Limitations. The propulsion drive
system limitations must be established so that they do not exceed the
corresponding limits approved for the engine, propeller shaft, and
drive system components.
(i) For the Dual Pac engine, takeoff power must be limited by--
(A) The powerplant maximum rotational speed for takeoff power, and
the maximum rotational propeller shaft speed may not be greater than
the values determined by the propulsion drive system type design, or
the maximum value shown during type tests.
(B) The time limit for the use of power, gas temperature, and speed
corresponding to the limitations established in paragraph (i) of this
section.
(C) The powerplant maximum allowable gas temperature at maximum
allowable power or torque for each engine, considering the power input
limitations of the transmission with all engines operating; and
(D) The powerplant maximum allowable gas temperature at maximum
allowable power or torque for each engine, considering the power input
limitations of the transmission with one engine inoperative.
(ii) For the Dual Pac engine, continuous power must be limited by--
(A) The powerplant maximum rotational speed for continuous power.
The maximum rotational propeller shaft speed may not be greater than
the values determined by the propulsion drive system type design
maximum value shown during type tests.
(B) The powerplant maximum allowable gas temperature for continuous
power and the maximum allowable power or torque for each engine,
considering the power input limitations of the transmission with both
engines operating; and
(C) The powerplant maximum allowable gas temperature at maximum
allowable power or torque for each engine, considering the power input
limitations of the transmission with one engine inoperative.
(3) Propulsion Drive System Instruments. Connections for the
following instruments must be provided for any gearbox or transmission:
(i) An oil pressure warning device for each pressure-lubricated
gearbox to indicate when the oil pressure falls below a safe value;
(ii) A low oil quantity warning indicator for each gearbox, if
lubricant is self-contained;
(iii) An oil temperature warning device to indicate unsafe oil
temperatures in each gearbox;
(iv) A tachometer for each propeller shaft;
(v) A torquemeter for each transmission driving a propeller shaft;
and
(vi) A chip detecting and indicating system for each gearbox.
(4) Propulsion Drive System Endurance Tests. Each part tested, as
prescribed in this section, must be in serviceable condition at the end
of the tests. No intervening disassembly that might affect these
results may be conducted.
(i) Endurance tests; general. The propulsion drive system, as
defined in paragraph (c)(1) must be tested as prescribed in paragraphs
(c)(4)(ii) through (c)(4)(ix), for at least 200 hours plus the time
required to meet paragraph (c)(4)(ix). For the 200-hour portion, these
tests must be conducted as follows:
(A) twenty each, ten-hour test cycles consisting of the test times
and procedures in paragraphs (c)(4)(ii) through (c)(4)(viii); and
(B) The test torque must be determined by actual powerplant
limitations.
(ii) Endurance tests; takeoff torque run. The takeoff torque run
endurance test must be conducted as follows:
(A) The takeoff torque run must consist of a one-hour run on the
engine(s) at the torque corresponding to takeoff power, but with the
engine power setting alternately cycled every five minutes to as low an
engine idle speed as practicable.
(B) Deceleration and acceleration of the engines and/or of
individual engines and drive systems must be performed at the maximum
rate. (This corresponds to a one-second power setting change from idle
to takeoff setting, and one second from takeoff setting to idle.)
(C) The time duration of all engines at takeoff power setting must
total one hour and does not include the time required to go from
takeoff to idle and back to takeoff speed.
(iii) Endurance tests; maximum continuous run. Three hours of
continuous operation, at the torque corresponding to maximum continuous
power and speed, must be conducted.
(iv) Endurance tests; 90 percent of maximum continuous run. One
hour of continuous operation, at the torque corresponding to 90 percent
of maximum continuous power, must be conducted at maximum continuous
rotational propeller shaft speed.
(v) Endurance tests; 80 percent of maximum continuous run. One hour
of continuous operation, at the torque corresponding to 80 percent of
maximum power, must be conducted at the minimum rotational propeller
shaft speed intended for this power.
(vi) Endurance tests; 60 percent of maximum continuous run. Two
hours of continuous operation, at the torque corresponding to 60
percent of maximum continuous power, must be conducted at the minimum
rotational propeller shaft speed intended for this power.
(vii) Endurance tests; engine malfunctioning run. It must be
determined whether malfunctioning of components, such as the engine
fuel or ignition systems, or unequal engine power can cause dynamic
conditions detrimental to the drive system. If so, a suitable number of
hours of operation must be accomplished under those conditions, one
hour of which must be included in each cycle, and the remaining hours
of which must be accomplished at the end of 20 cycles. This testing is
to be equally divided between the following four conditions: (1) Engine
#1 ``ON''/engine #2 ``IDLE''; (2) engine #1 ``ON''/engine #2 ``OFF'';
(3) engine #1 ``IDLE''/engine #2 ``ON''; (4) engine #1 ``OFF''/engine
#2 ``ON''. If no detrimental condition results, an additional hour of
operation in compliance with paragraph (ii) of this section must be
conducted.
(viii) Endurance tests; overspeed run. One hour of continuous
operation must be conducted at the torque corresponding to maximum
continuous power, and at 110 percent of rated maximum continuous
rotational propeller shaft speed. It the overspeed is limited to less
than 110 percent of maximum continuous speed by the speed and torque
limiting devices, the speed used must be the highest speed allowable,
assuming that speed and torque limiting devices, if any, function
properly.
(ix) Endurance tests; one-engine-out application. A total of 160
full differential power applications must be made at takeoff torque and
RPM. If, during these tests, it is found that a critical dynamic
condition exists, an investigative assessment to determine the cause
shall be performed throughout the torque/speed range. In each of the
160 engine power setting cycles (160 per engine drive branch) a full
differential power application must be performed. In each cycle, the
transition from clutch engagement to disengagement must occur at the
critical condition for clutch and shaft wear.
(5) Additional Propulsion Drive System Tests. Additional dynamic,
endurance, and operational test and vibratory investigations must be
performed to determine that the drive mechanism is safe. The following
additional tests and conditions apply:
(i) If the torque output of all engines to the transmission can
exceed the highest engine or transmission torque limit, the following
tests must be conducted. Under conditions associated with all engines
operating, apply 200 cycles to the drive system for 10 seconds each of
a torque that is at least equal to the lesser of--
(A) The maximum torque used in complying with paragraph (4)(ii)
plus 10 percent; or
(B) The maximum torque attainable under normal operating
conditions, assuming that any torque limiting devices function
properly.
(ii) With each engine alternately inoperative, apply to the
remaining transmission inputs the maximum transient torque attainable
under normal operating condition, assuming that any torque limiting
devices function properly. Each transmission input must be tested at
this maximum torque for at least 15 minutes.
(iii) After completion of the 200 hour endurance test and without
intervening major disassembly, the drive system must be subjected to 50
overspeed runs, each 30 3 seconds in duration, at a speed
of at least 120 percent of maximum continuous speed, or other maximum
overspeed that is likely to occur, plus a margin of speed approved by
the Administrator for that overspeed condition. These runs must be
conducted as follows:
(A) Overspeed runs must be alternated with stabilizing runs from 1
to 5 minutes duration, each 60 to 80 percent of maximum continuous
speed.
(B) Acceleration and deceleration must be accomplished in a period
no longer than 10 seconds, and the time for changing speeds may not be
deducted from the specified time for the overspeed runs.
(iv) Each part tested, as prescribed in this section, must be in
serviceable condition at the end of the tests. No intervening
disassembly that might affect test results may be conducted.
(v) If drive shaft couplings are used and shaft misalignment or
deflections are probable, loads must be determined in establishing the
installation limits affecting misalignment. These loads must be
combined to show adequate fatigue life.
(vi) The vibration test specified in 33.83 must be applied to
engine-furnished components of the propulsion drive system. The test
must include the gear case and each component in the combining gear box
whose failure due to vibration could cause unsafe operation of the
engine.
(6) Propulsion Drive System Shafting Critical Speed. The critical
speeds of any shafting must be determined by test, except that
analytical methods may be used if reliable methods of analysis are
available for the particular design.
(i) If any critical speed lies within, or close to, the operating
ranges for idling and power on conditions, the stresses occurring at
that speed must be within design limits. This must be shown by tests.
(ii) If analytical methods are used and show that no critical speed
lies within the permissible operating ranges, the margins between the
calculated critical speeds and the limits of the allowable operating
ranges must be adequate to allow for possible variations between the
computed and actual values.
Issued in Burlington, Massachusetts, on January 26, 1994.
Jay J. Pardee,
Acting Manager, Engine and Propeller Directorate, Aircraft
Certification Service.
[FR Doc. 94-2561 Filed 2-3-94; 8:45 am]
BILLING CODE 4910-13-M
