Special Conditions; Soloy Dual Pac, Inc., Model Soloy Dual Pac Engine

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]

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