[Federal Register Volume 62, Number 33 (Wednesday, February 19, 1997)]
[Rules and Regulations]
[Pages 7335-7338]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-4067]



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Rules and Regulations
                                                Federal Register
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Federal Register / Vol. 62, No. 33 / Wednesday, February 19, 1997 / 
Rules and Regulations

[[Page 7335]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 33

[Docket No. 93-ANE-14; No. 33-ANE-01]


Special Conditions; Soloy Corporation, Soloy Dual Pac Engine 
(Formally Soloy Dual Pac, Inc.)

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Soloy Corporation, 
Soloy Dual Pac engine (formally Soloy Dual Pac Inc.). This engine will 
have a novel design feature associated with its configuration. The 
Soloy Dual Pac engine is a propulsion system in which two Pratt & 
Whitney Canada (PWC) Model PT6 turbine engines are combined through a 
common gearbox to drive a single output propeller shaft. The Soloy Dual 
Pac engine is intended to provide a degree of continuous operation 
following the failure of one of the PWC Model PT6 engines. The 
applicable regulations do not contain adequate or appropriate safety 
standards for such a configuration. These special conditions contain 
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).

EFFECTIVE DATES: March 21, 1997.

FOR FURTHER INFORMATION CONTACT:
Kathrine Rask, Seattle Aircraft Certification Office, Propulsion 
Branch, ANM-140S, FAA, Northwest Mountain Region, 1601 Lind Avenue SW., 
Renton, Washington 98055-4056, Telephone (206) 227-1547; fax (206) 227-
1181.

SUPPLEMENTARY INFORMATION: 

Background

General

    On November 9, 1990, Soloy Corporation applied for a supplemental 
type certificate for the Soloy Dual Pac engine. The Soloy Dual Pac 
engine is a propulsion concept in which two PWC Model PT6 engines, 
currently approved under Type Certificate No. E4EA, drive a single 
propeller shaft through a combining gearbox. The Soloy 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 Soloy Dual Pac engine is to be based on the type 
certificate of the PWC Model PT6 engine. On February 4, 1994, the FAA 
published a notice of proposed special conditions (59 FR 5356) for 
``Soloy Dual Pac, Inc., Soloy Dual Pac Engine'', requesting public 
comments. Since that publication, the name has changed from Soloy Dual 
Pac, Inc., to Soloy Corporation.

Safety Analysis

    The certification basis of the PWC Model PT6 engine was established 
before the introduction of Sec. 33.75 of the Federal Aviation 
Regulation (FAR) (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 Soloy Dual Pac engine program.
    Also, one objective of the Soloy Dual Pac engine is to provide 
continued operation after the failure of one PWC Model PT6 engine. 
While the safety analysis regulations of Sec. 33.75 are more extensive 
than those of the PWC Model PT6 engine certification basis, they still 
do not address this special ``continue to run'' objective.
    Therefore, in light of the above, it was proposed that a safety 
analysis requirement, modeled after Sec. 33.75 and expanded to address 
continued operation after a single engine failure, be included in the 
Soloy Dual Pac engine certification basis.

Uncontained Engine Failure

    It is assumed that the Soloy 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 must be 
addressed initially during the Soloy Dual Pac engine certification 
program, and may also be addressed during the aircraft installation 
certification program.
    As stated above, one objective of a Soloy Dual Pac engine-equipped 
aircraft could be continued safe flight and landing after the failure 
of one PWC Model PT6 engine. In order for the Soloy 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 Soloy 
Dual Pac engine, such an event could end all torque production. 
Therefore, the Soloy Dual Pac engine must demonstrate that the two PWC 
Model 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 
accessory gearboxes, have been evaluated during the course of engine 
block tests and other engine certification activities. Transmissions 
such as those used in

[[Page 7336]]

rotorcraft, however, have been addressed in rotor drive criteria 
contained in rotorcraft certification regulations. Since the Soloy Dual 
Pac engine propulsion drive system is part of the engine, the changes 
to part 23 of the FAR, 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 
Sec. 33.87 of the FAR (amended through Amendment 33-5), will 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 standards to address the turbine interface with the 
gearbox.

Type Certification Basis

    Under the provisions of Sec. 21.101 of the FAR, Soloy Corporation, 
must show that the Soloy 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, dated March 28, 1955.
    (c) FAR part 33, Airworthiness Standards: Aircraft Engines, 
effective February 1, 1965, as amended by Amendments 33-1 through 33-5 
inclusive.
    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 part 33 of the 
FAR, effective February 1, 1965, as amended by Amendment 33-1 through 
33-5 inclusive, 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 part 34 of the FAR (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 unusual design feature. Therefore, the Administrator 
prescribes special conditions under the provision 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).

Discussion of Comments

    Interested persons have been afforded the opportunity to 
participate in the making of these special conditions. One comment were 
received supporting the additional safety standards for the Soloy Dual 
Pac engine in the notice of proposed special conditions as published.
    The FAA has gained a better technical understanding of the Soloy 
Dual Pac engine design since the notice of proposed special conditions 
were published in the Federal Register.
    One of the critical systems of the Soloy Dual Pac engine is the 
single propeller. Paragraph(c)(1)(iv) was developed to ensure that a 
loss of oil pressure to the propeller governing system or the propeller 
shaft lubrication would not result in imminent loss of propeller speed 
or control. The zero oil pressure test as published in the notice of 
proposed special conditions does not adequately address these concerns. 
The blade pitch control system of the Soloy Dual Pac engine propeller 
installation is expected to contain a fail safe setting that is not 
equivalent to the 100 percent output speed required in the notice of 
proposed special conditions. When the propeller governor looses oil 
pressure, it will automatically revert to a predetermined mechanical 
limit, a so called ``get home'' pitch and speed. In addition, the 15 
minute requirement (the notice of proposed special conditions stated 
``15 seconds,'' however this was a typographical error) is not adequate 
for the type of aircraft installations where the Soloy Dual Pac is 
expected to be used. These airplanes, operating under part 121 of the 
FAR, will be allowed to operate over routes that contain a point up to 
one hour flying time from an adequate airport. The test of less than 
one hour of continued safe operation would not fulfill the intent of 
the paragraph (c)(1)(iv). The FAA has determined that paragraph 
(c)(1)(iv) as proposed, which set forth requirements for a zero oil 
pressure test of the gearbox, does not address the intent of this 
paragraph and therefore it is modified in these final special 
conditions. The revised test requirements in the final special 
conditions address more accurately the airplane failure scenario 
intended to be evaluated. However, the demonstrated torque and 
rotational speed must be included in the instruction manual for 
installing and operating the engine required in Sec. 33.5 of the FAR.

Conclusion

    This action affects only certain novel or unusual design features 
on one model engine configuration. It is not a rule of general 
applicability, and 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 citation for part 33 continues to read as follows:

    Authority: 49 U.S.C. 106(g); 40113, 44701, 44702, 44704

The Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special conditions are issued as part of 
the type certification basis for the Soloy Corporation, 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 Soloy Dual Pac engine will not cause the Soloy Dual Pac engine 
to--
    (1) Catch fire;
    (2) Burst (release hazardous fragments through the engine case);

[[Page 7337]]

    (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 PWC 
PT6 engine, in the event of uncontained engine failure of the other PWC 
Model 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 bearings for 
shafts, brake assemblies, clutches, gearboxes, transmissions, any 
attached accessory pads 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, 
if 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 
continue safe operation, although not necessarily without damage, at a 
torque and rotational speed prescribed by the applicant which is 
determined to be the most critical of the anticipated flight 
conditions. The drive system shall operate at this condition for at 
least one hour after perception by the flight crew of the lubrication 
system failure or loss of lubricant. The demonstrated torque and 
rotational speed must be included in the instructional manual for 
installing and operating the engine required in Sec. 33.5 of the 
Federal Aviation Regulations (FAR).
    (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 Soloy 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 or torque of each engine, considering the power input 
limitations of the transmission with one engine inoperative.
    (ii) For the Soloy 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 of 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) Powerplant maximum allowable gas temperature at maximum 
allowable power or torque of 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 gear box, 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 a 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 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

[[Page 7338]]

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 system 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 take off 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 conditions 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. if 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<plus-minus>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 Sec. 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 February 7, 1997.
James C. Jones,
Acting Manager, Engine and Propeller Directorate, Aircraft 
Certification Service.
[FR Doc. 97-4067 Filed 2-18-97; 8:45 am]
BILLING CODE 4910-13-M