[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