[Federal Register Volume 64, Number 176 (Monday, September 13, 1999)]
[Rules and Regulations]
[Pages 49367-49373]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-23721]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 23

[Docket No. CE149; Special Condition 23-097-SC]


Special Conditions: Soloy Corporation Model Pathfinder 21 
Airplane; Airframe.

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Soloy Corporation 
Model Pathfinder 21 airplane. The Model Pathfinder 21 airplane is a 
Cessna Model 208B airplane as modified by Soloy Corporation to be 
considered as a multiengine, part 23, normal category airplane. The 
Model Pathfinder 21 airplane will have a novel or unusual design 
features associated with installation of the Soloy Dual Pac propulsion 
system, which consists of two Pratt & Whitney Canada Model PT6D-114A 
turboprop engines driving a single, Hartzell, five-blade propeller. The 
applicable airworthiness regulations do not contain adequate or 
appropriate safety standards for this design feature. These special 
conditions contain the additional safety standards that the 
Administrator considers necessary to establish a level of safety 
equivalent to that established by the existing airworthiness standards.

EFFECTIVE DATE: October 13, 1999.

FOR FURTHER INFORMATION CONTACT: Dave Keenan, Federal Aviation 
Administration, Aircraft Certification Service, Small Airplane 
Directorate, ACE-111, 601 East 12th Street, Kansas City, Missouri 
64106; 816-426-5688, fax 816-426-2169.

SUPPLEMENTARY INFORMATION:

Background

    On February 6, 1992, Soloy Corporation applied for a supplemental 
type certificate (STC) for the Model Pathfinder 21 airplane, which 
would modify the Cessna Model 208B airplane by installing the Soloy 
Dual Pac propulsion system. This propulsion system consists of two 
Pratt & Whitney Canada (PWC) Model PT6D-114A turboprop engines driving 
a single, Hartzell, five-blade propeller through a combining gearbox. 
Soloy Corporation is seeking approval for this airplane, equipped with 
a Soloy Dual Pac propulsion system, as a normal category multiengine 
airplane. Title 14 CFR part 23 is not adequate to address a multiengine 
airplane with a single propeller. Hence, the requirement for these 
proposed special conditions, which will be applied in addition to the 
applicable sections of part 23.
    The Soloy Dual Pac propulsion system is mounted in the nose of the 
Model Pathfinder 21 airplane. With this arrangement, an engine failure 
does not cause an asymmetric thrust condition that would exist with a 
conventional twin turboprop airplane. This asymmetric thrust compounds 
the flightcrew workload following an engine failure. The Model 
Pathfinder 21 airplane configuration has the potential to substantially 
reduce this workload.
    Since the Model Pathfinder 21 airplane produces only centerline 
thrust, the only direct airplane control implications of an engine 
failure are the change in torque reaction and propeller slipstream 
effect. These transient characteristics require substantially less crew 
action to correct than an asymmetric thrust condition and do not 
require constant effort by the flightcrew to maintain control of the 
airplane for the remainder of the flight.

Safety Analysis

    The FAA has conducted a safety analysis that recognizes both the 
advantages and disadvantages of the proposed Model Pathfinder 21 
airplane. The scope of this safety analysis was limited to the areas 
affected by the unique propulsion system installation and assumes 
compliance with the design-related requirements of these proposed 
special conditions. The FAA examined the accident and incident history 
of small twin turboprop operations for the years of 1983 to 1994 in the 
United States and the United Kingdom. The FAA evaluated each event and 
determined if the outcome,

[[Page 49368]]

given the same pilot, weather, and airplane except with centerline 
thrust and one propeller, would have been more favorable, less 
favorable, or unchanged. Examination of the incident data revealed a 
number of failure modes that, if not addressed as part of the Model 
Pathfinder 21 airplane design, could result in a potential increase in 
the number of accidents for the Model Pathfinder 21 airplane compared 
to the current fleet. Examples of such failure modes include loss of a 
propeller blade tip or failure of the propeller control system. 
Although these proposed special conditions contain provisions to 
prevent catastrophic failures of the remaining non-fail-safe components 
of the Model Pathfinder 21 airplane after compliance with the design 
related requirements, the analysis assumes that these components will 
fail in a similar manner to the failures contained in the incident 
data. Given these assumptions, the FAA determined that the projected 
accident rate of the Model Pathfinder 21 airplane would be equal to or 
lower than the current small twin turboprop airplane fleet. Considering 
that analysis, the FAA has determined that the advantages of centerline 
thrust compensate for the disadvantages of the non-fail-safe design 
features. Once that determination was made, these proposed special 
conditions were formulated with the objective of substantially reducing 
or eliminating risks associated with the non-redundant systems and 
components of the Model Pathfinder 21 airplane design that have been 
identified and providing a level of safety equivalent to that of 
conventional multiengine airplanes.
    The FAA data review conducted to prepare these proposed special 
conditions is applicable only to the Model Pathfinder 21 airplane. For 
the concept of a single-propeller, multiengine airplane to be extended 
to other projects, a separate analysis of the accident and incident 
data for similarly sized airplanes would be required. If the advantages 
of centerline thrust compensated for the disadvantages of the non-fail-
safe components, based on the service history of similarly sized 
airplanes, development of separate special conditions would be 
required.

Type Certification Basis

    Under the provisions of 14 CFR part 21, Sec. 21.101, Soloy 
Corporation must show that the Model Pathfinder 21 airplane continues 
to meet the applicable provisions of the regulations incorporated by 
reference in Type Certificate (TC) Data Sheet A37CE or the applicable 
regulations in effect on the date of application for change. The 
regulations incorporated by reference are commonly referred to as the 
``original type certification basis.'' The regulations incorporated by 
reference in TC No. A37CE are as follows:
    The type certification basis for Cessna Model 208B airplanes shown 
on TC Data Sheet A37CE for parts not changed or not affected by the 
changes proposed by Soloy Corporation is part 23 of the Federal 
Aviation Regulations dated February 1, 1965, as amended by Amendments 
23-1 through 23-28; part 36 dated December 1, 1969, as amended by 
Amendments 36-1 through 36-18; Special Federal Aviation Regulations 
(SFAR) 27 dated February 1, 1974, as amended by Amendments 27-1 through 
27-4. Soloy Corporation must show that the Model Pathfinder 21 airplane 
meets the applicable provisions of part 23, including multiengine 
designated sections, as amended by Amendment 23-42 (the Pathfinder 21 
type certification basis is based on the date of STC application: 
February 6, 1992) for parts changed or affected by the change. Soloy 
Corporation has also elected to comply with Sec. 23.561, Emergency 
Landing Conditions--General (Amendment 23-48); Sec. 23.731, Wheels 
(Amendment 23-45); Sec. 23.733, Tires (Amendment 23-45); Sec. 23.783, 
Doors (Amendment. 23-49); Sec. 23.807, Emergency Exits (Amendment 23-
49); Sec. 23.811, Emergency Exit Marking (Amendment 23-46); 
Sec. 23.901, Installation (Amendment 23-51); Sec. 23.955, Fuel Flow 
(Amendment 23-51); Sec. 23.1041, Cooling--General (Amendment 23-51); 
Sec. 23.1091, Air Induction System (Amendment 23-51); Sec. 23.1181, 
Designated Fire Zones; Regions Included (Amendment 23-51); 
Sec. 23.1189, Shutoff Means (Amendment 23-43); Sec. 23.1305, Powerplant 
Instruments (Amendment 23-52); and Sec. 23.1351, Electrical Systems and 
Equipment--General (Amendment 23-49). The type certification basis for 
the Model Pathfinder 21 airplane also includes parts 34 and 36, each as 
amended at the time of certification. Soloy Corporation may also elect 
to comply with subsequent part 23 requirements to facilitate operators' 
compliance with corresponding part 135 requirements. The type 
certification basis for this airplane will include exemptions, if any; 
equivalent level of safety findings, if any; and the special conditions 
adopted by this rulemaking action.
    If the Administrator finds that the applicable airworthiness 
regulations (part 23, as amended) do not contain adequate or 
appropriate safety standards for the Model Pathfinder 21 airplane 
because of a novel or unusual design feature, special conditions are 
prescribed under the provisions of Sec. 21.16.
    Special conditions, as appropriate, are issued in accordance with 
Sec. 11.49 after public notice, as required by Sec. 11.28 and 
Sec. 11.29(b), and become part of the type certification basis in 
accordance with Sec. 21.101(b)(2).
    Special conditions are initially applicable to the model for which 
they are issued. Should the applicant apply for an STC to modify any 
other model included on the same TC to incorporate the same novel or 
unusual design feature, the special conditions would also apply to the 
other model under the provisions of Sec. 21.101(a)(1).
    The Soloy Dual Pac was certified as a propulsion system under part 
33 and special conditions in Docket No. 93-ANE-14; No. 33-ANE-01 (62 FR 
7335, February 19, 1997) under STC No. SE00482SE to the PWC Model PT6 
engine TC E4EA. Those special conditions were created in recognition of 
the novel and unusual features of the proposal, specifically the 
combining gearbox.

Novel or Unusual Design Features

    The Model Pathfinder 21 will incorporate a novel or unusual design 
feature by installing the Soloy Dual Pac propulsion system, which 
consists of two PWC Model PT6D-114A engines driving a single, Hartzell, 
five-blade propeller through a Soloy-designed combining gearbox. The 
combining gearbox 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.

Propulsion System

    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. The propulsion 
drive system for this multiengine installation must be designed with a 
``continue to run'' philosophy. This means that it must be able to 
power the propeller after failure of one engine or failure in one side 
of the drive system, including any gear, bearing, or element expected 
to fail. Common failures, such as oil pressure loss or gear tooth 
failure, in the

[[Page 49369]]

propulsion drive system must not prevent the propulsion system from 
providing adequate thrust. These design requirements, and other 
propulsion drive system requirements, are included in the part 33 
special conditions, and, therefore, are required as part of these 
proposed special conditions.
    Section 23.903(b)(1) states, in part, ``Design precautions must be 
taken to minimize the hazards to the airplane in the event of a rotor 
failure.'' Part 33 containment requirements address blade failures but 
do not require containment of failed rotor disks; therefore, 
Sec. 23.903(b)(1) requires that airplane manufacturers minimize the 
hazards in the event of a rotor failure. This is done by locating 
critical systems and components out of impact areas as much as 
possible. The separation inherent in conventional twin engine 
arrangements by locating the engines on opposite sides of the fuselage 
provides good protection from engine-to-engine damage. Although most 
multiengine installations have the potential for an uncontained failure 
of one engine damaging the other engine, service history has shown that 
the risk of striking the opposite engine is extremely low.
    The Model Pathfinder 21 airplane propulsion system installation 
does not have the inherent engine-to-engine isolation of a conventional 
twin turboprop airplane. For the Model Pathfinder 21 airplane to obtain 
a level of safety equivalent to that of a conventional multiengine 
airplane, the effects of rotor failure must be addressed. Soloy 
Corporation must demonstrate that the engine type in relevant 
installations has at least ten million hours of service time without a 
high energy rotor failure (for example, disks, hubs, compressor wheels, 
and so forth). Additionally, for any lower energy fragments released 
during this extensive service life of the engine (for example, blades), 
a barrier must be placed between the engines to contain these low 
energy fragments. Even after installation of a barrier, engine-to-
engine isolation following failure of either engine could be 
compromised through the common mount system or shared system interfaces 
such as firewalls, electrical busses, or cowlings. Soloy Corporation 
must, therefore, demonstrate any loads transmitted through the common 
mount system as a result of an engine failure do not prevent continued 
safe flight and landing with the operating engine.
    Section 23.903(b)(1) also addresses damage caused by engine case 
burn-through. Engine case burn-through results in a concentrated flame 
that has the capability to burn through the firewall mandated by 
Sec. 23.1191; therefore, Sec. 23.903(b)(1) requires that design 
precautions must be taken to minimize the hazards to the airplane in 
the event of a fire originating in the engine that burns through the 
engine case. Similar to uncontained engine failures, the conventional 
multiengine airplane arrangement provides inherent protection from 
engine-to-engine damage associated with engine case burn-through by 
placing the engines on opposite sides of the fuselage. The Model 
Pathfinder 21 airplane propulsion system does not have this inherent 
isolation; therefore, the FAA is requiring that engine type in a 
relevant installation to have either at least ten million hours of 
service time without an engine case burn-through, or a firewall able to 
protect the operating engine from engine case burn-through installed 
between the engines.
    Soloy Corporation is not required to show compliance to Sec. 21.35, 
per Sec. 21.115 because the Model Pathfinder 21 airplane certification 
is being conducted under an STC project. Section 21.35(f)(1), Flight 
Tests, requires aircraft incorporating turbine engines of a type not 
previously used in a type certificated aircraft to operate for at least 
300 hours with a full complement of engines that conform to a type 
certificate as part of the certification flight test. The propulsion 
system installation is, however, different from any other airplane 
previously certified; therefore, the FAA is requiring as part of these 
special conditions that Soloy Corporation show compliance with 
Sec. 21.35(f)(1).

Propeller Installation

    As demonstrated by the data discussed in the Safety Analysis 
section, propeller blade failures near the hub result in substantial 
airplane damage on a conventional twin turboprop airplane. One of the 
eight events was catastrophic. Blade debris has damaged critical 
components and structure of the airplane, and large unbalance loads in 
the propeller have led to engine, mount, and wing structural failure. 
In contrast, service history has demonstrated that blade tip failures 
are not necessarily catastrophic on a conventional multiengine airplane 
because the flightcrew is able to secure the engine with the failed 
propeller and safely land the airplane. However, if the Model 
Pathfinder 21 airplane's single propeller failed near the tip, the 
failure would be likely to result in a catastrophic accident caused by 
the total loss of thrust capability and severe vibration. Other 
propeller system structural failures would be equally catastrophic; 
therefore, steps must be taken to reduce the potential for propeller 
system structural failures.
    As discussed earlier, the FAA has determined additional testing is 
required for non-redundant components to ensure that equivalency to the 
fail-safe and isolation requirements of Sec. 23.903(c) is met. The 
Model Pathfinder 21 airplane's single propeller system must be 
installed and maintained in such a manner as to substantially reduce or 
eliminate the occurrence of failures that would preclude continued safe 
flight and landing. To ensure the propeller installation and production 
and maintenance programs are sufficient to achieve the fail-safe 
equivalency requirement, these proposed special conditions include a 
2,500 cycle validation test. This corresponds to the FAA's estimated 
annual usage for a turboprop airplane operating in scheduled service. 
An airplane cycle includes idle, takeoff, climb, cruise, descent, and 
reverse. The test must utilize production parts installed on the engine 
and should include a wide range of ambient and wind conditions, several 
full stops, and validation of scheduled and unscheduled maintenance 
practices.
    Furthermore, these special conditions require identification of the 
critical parts of the propeller assembly, which are components whose 
failure during ground or flight operation could cause a catastrophic 
effect on the airplane, including loss of the ability to produce 
controllable thrust. The FAA is proposing to require that a critical 
parts plan, modeled after plans required by Joint Aviation Requirements 
27 and 29 for critical rotorcraft components, be established and 
implemented for the critical components of the propeller assembly. This 
plan draws the attention of the personnel involved in the design, 
manufacture, maintenance, and overhaul of a critical part to the 
special nature of the part. The plan should define the details of 
relevant special instructions to be included in the Instructions for 
Continued Airworthiness. The Instructions for Continued Airworthiness, 
required by Sec. 23.1529, should contain life limits, mandatory 
overhaul intervals, and conservative damage limits for return to 
service and repair, as appropriate, for the critical parts identified 
in accordance with these special conditions.
    On a conventional multiengine airplane, the flightcrew will secure 
an engine to minimize effects of propeller imbalance. Most of these 
airplanes also incorporate quick acting manual or

[[Page 49370]]

automatic propeller feathering systems that further reduce the time the 
airplane is exposed to the effects of propeller imbalance. In addition 
to the propeller blade failures discussed earlier, the unbalanced 
condition could be caused by a propeller system failure such as loss of 
a de-icing boot, malfunction of a de-icing boot in icing conditions, an 
oil leak into a blade butt, asymmetric blade pitch, or a failure in a 
counterweight attachment. The Model Pathfinder 21 airplane design does 
not provide any means to reduce the vibration produced by an unbalanced 
propeller; therefore, these proposed special conditions require that 
the engines, propulsion drive system, engine mounts, primary airframe 
structure, and critical systems must be designed to function safely in 
the high vibration environment generated by those less severe propeller 
failures. In addition, the degree of flight deck vibration must not 
jeopardize the crew's ability to continue to operate the airplane in a 
safe manner. Component failures that generate vibrations beyond the 
capability of the airplane must be addressed as a critical part in the 
same manner as required for propeller blade failures.

Propeller Control System

    Propeller control system failures on a conventional twin engine 
airplane may result in a one-engine-inoperative configuration. To 
ensure an equivalent level of safety in the event of a propeller 
control system failure, these special conditions require that the Model 
Pathfinder 21 airplane propulsion system be designed such that the 
airplane meets the one-engine-inoperative requirements of Sec. 23.53 
and Sec. 23.67 after the most critical propeller control system 
failure.
    There are several means to accomplish these special condition 
elements. Soloy Corporation plans to address them by providing a 
mechanical high-pitch stop, which would be set to a ``get home'' pitch 
position, thereby preventing the propeller blades from rotating to a 
feather-pitch position when oil pressure is lost in the propeller 
control system. This would allow the propeller to continue to produce a 
minimum amount of thrust as a fixed-pitch propeller. These special 
conditions provide design requirements that the FAA has determined are 
critical to a default fixed-pitch position feature. These include 
maintaining engine and propeller limits following an automatic or 
manual pitch change, the ability to manually select and deselect the 
default fixed-pitch position in flight in the event of a propeller 
control system failure that does not result in a loss of oil pressure, 
and the means to indicate to the flightcrew when the propeller is at 
the default fixed-pitch position.

Propulsion Instrumentation

    On a conventional multiengine airplane, the pilot has positive 
indication of an inoperative engine created by the asymmetric thrust 
condition. The airplane will not yaw when an engine or a portion of the 
propulsion drive system fails because of the centerline thrust of the 
Model Pathfinder 21 airplane propulsion system installation. The 
flightcrew will have to rely on other means to determine which engine 
or propulsion drive system element has failed so as to secure the 
correct engine; therefore, these special conditions require that a 
positive indication of an inoperative engine or a failed portion of the 
propulsion drive system must be provided.
    Section 23.1305 requires instruments for the fuel system, engine 
oil system, fire protection system, and propeller control system. This 
rule is intended for powerplants consisting of a single-engine, 
gearbox, and propeller. To protect the portions of the propulsion drive 
system that are independent of the engines, additional instrumentation, 
which includes oil pressure, oil quantity, oil temperature, propeller 
speed, gearbox torque, and chip detection, is required.

Fire Protection System

    On a conventional twin engine airplane, the engines are 
sufficiently separated to eliminate the possibility of a fire spreading 
from one engine to another. Since the Soloy Dual Pac propulsion system 
is installed in the nose of the airplane, the engines are separated 
only by a firewall. The fire protection system of the Model Pathfinder 
21 airplane must include features to isolate each fire zone from any 
other zone and the airplane to maintain isolation of the engines during 
a fire; therefore, these special conditions mandate that the firewall 
required by Sec. 23.1191 be extended to provide firewall isolation 
between either engine and the propulsion drive system. These special 
conditions require that heat radiating from a fire originating in any 
fire zone must not affect components in adjacent compartments in such a 
way as to endanger the airplane.

Airplane Performance

    Section 23.67, and paragraphs in Sec. 23.53, Sec. 23.69 and 
Sec. 23.75, provide performance requirements for multiengine airplanes 
with one engine inoperative. These rules are not adequate for 
multiengine, single propeller airplanes. In these special conditions, 
the airplane configuration requirements specified in Sec. 23.53(b)(1), 
Sec. 23.67(c)(1), Sec. 23.69(b), and Sec. 23.75(g) have been adapted to 
accommodate the propeller system of the Model Pathfinder 21 airplane to 
ensure a level of safety equivalent to that of conventional multiengine 
airplanes.

Airspeed Indicator

    Section 23.1545(b)(5) provides one-engine-inoperative marking 
requirements for the airspeed indicator. This rule is not adequate to 
address critical propeller control system failures on the Model 
Pathfinder 21 airplane. As a result, these special conditions require 
that the airspeed markings required by Sec. 23.1545(b)(5) be based on 
the most critical flight condition between one engine inoperative or a 
failed propeller control system in order to ensure a level of safety 
equivalent to that of conventional multiengine airplanes.

Airplane Flight Manual

    Sections 23.1585 and 23.1587 require pertinent information to be 
included in the Airplane Flight Manual (AFM). These rules are not 
adequate to address critical propeller control system failures on the 
Model Pathfinder 21 airplane. As a result, these special conditions 
require that the critical procedures and information required by 
Sec. 23.1585, paragraph (c), and Sec. 23.1587, paragraphs (c)(2) and 
(c)(4), include consideration of these critical propeller control 
system failures in order to ensure a level of safety equivalent to that 
of conventional multiengine airplanes.

Discussion of Comments

    Notice of proposed special conditions, Notice No. 23-98-05-SC, 
Docket No. CE149, for the Soloy Corporation Model Pathfinder 21 
airplane was published in the Federal Register on March 25, 1999 (64 FR 
14401). On April 21, 1999, Soloy Corporation requested that the comment 
period be extended to allow them sufficient time to comment on the 
proposals. The FAA reopened the comment period in the Federal Register 
dated June 1, 1999 (64 FR 29247). The new comment period closed July 1, 
1999. The following is a summary of the comments received and a 
response to each comment.
    Only one commenter, Hartzell Propeller, Inc., responded to the 
notice of proposed special conditions. Their comments are summarized 
below:
    1. Comment: This requirement has no clearly stated objectives. Is 
the purpose of each cycle to exercise the blade pitch mechanism or to 
subject the propeller to

[[Page 49371]]

fatigue cycles? This propeller is derived from a model that has been in 
service since the 1970's and has accumulated more than 4 million hours. 
From the propeller's perspective, there is no apparent benefit in 
adding 2,500 cycles to this experience.
    FAA Response: The purpose of this test is not only for the 
propeller alone, but also for the entire propulsion system of the 
Pathfinder 21 airplane. The object of this test is to establish the 
reliability of the engines, combining gearbox, and the propeller system 
together, as installed on the Pathfinder 21 airplane. This propulsion 
system reliability is being imposed due to a multiengine aircraft 
having only a single propeller.
    2. Comment: Balance criteria is very subjective. While most could 
agree when something is within acceptable limits, people's tolerance 
for unbalance can vary widely, making this requirement difficult to 
quantify. The ability of the propeller and airframe structure to 
withstand unbalance far exceeds that of the crew and passengers to 
tolerate it.
    FAA Response: Since this design is being classified as a 
multiengine aircraft, the flight crew will not have the ability to 
shutdown and feather an engine that is running rough due to some form 
of imbalance and continue on with the remaining powerplant. A 
Pathfinder 21 flightcrew may be required to operate the propulsion 
system at higher levels of imbalance than might be required of a 
conventional twin-engine airplane. This special condition is an attempt 
to quantify those levels of imbalance.
    3. Comment: There is no Sec. 23.53(b)(1)(ii). The text of 
Sec. 23.53(b)(1) specifically states both engines are operative. 
Section 23.67 makes specific reference to reciprocating engines and 
weights below 6,000 pounds, neither of which apply to the Pathfinder 
21.
    FAA Response: Section 23.53(b)(1)(ii), Takeoff speeds, in Amendment 
23-34 specifically states, ``Each normal, utility, and acrobatic 
category airplane, upon reaching a height of 50 feet above the takeoff 
surface, must have a speed of not less than the following: For 
multiengine airplanes, the higher of 1.3 VS1, or any lesser 
speed, not less than VX plus 4 knots, that is shown to be 
safe under all conditions, including turbulence and complete engine 
failure.''
    Section 23.67(c), Climb: one engine inoperative, in Amendment 23-42 
specifically states, ``For normal, utility, and acrobatic category 
turbine engine-powered multiengine airplanes the following apply: The 
steady climb gradient must be determined at each weight, altitude, and 
ambient temperature within the operational limits established by the 
applicant, with the airplane in the configuration as prescribed in 
paragraph (a) of this section. Each airplane must be able to maintain 
at least the following climb gradients with the airplane in the 
configuration prescribed in paragraph (a) of this section: 1.5 percent 
at a pressure altitude of 5,000 feet and a speed not less than 1.2 
VS1, and at standard temperature (41 deg.F); and 0.75 
percent at a pressure altitude of 5,000 feet at a speed not less than 
1.2 VS1 and 81 deg.F (standard temperature plus 40 deg.F). 
The minimum climb gradient specified in paragraphs (c)(2)(i) and (ii) 
of this section must vary linearly between 41 deg.F and 81 deg.F and 
must change at the same rate up to the maximum operating temperature 
approved for the airplane.''
    4. Comment: Any means to provide a secondary method to select blade 
angle would affect the type design of the propeller and introduce 
unconventional features which could adversely affect the established 
reliability of the propeller.
    FAA Response: The FAA agrees and this requirement has been removed 
from the special conditions.
    5. Comment: The special conditions state that ``a means to indicate 
to the flight crew when the propeller is at the default fixed-pitch 
position must be provided.'' The obvious signal that the propeller has 
defaulted to a fixed-pitch condition is a reduction in RPM.
    FAA Response: The FAA agrees and this requirement has been removed 
from the special conditions.

Applicability

    As discussed above, these special conditions are applicable to the 
Soloy Corporation Model Pathfinder 21 airplane . Should Soloy 
Corporation apply at a later date for a supplemental type certificate 
to modify any other model included on TC No. A37CE, the same novel or 
unusual design feature, the special conditions would apply to that 
model as well under the provisions of Sec. 21.101(a)(1).

Conclusion

    This action affects only certain novel or unusual design features 
on one model of airplanes. It is not a rule of general applicability, 
and it affects only the applicant who applied to the FAA for approval 
of these features on the airplane.

List of Subjects in 14 CFR Part 23

    Aircraft, Aviation safety, Signs and symbols.

Citation

    The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(g), 40113 and 44701; 14 CFR 21.16 and 
21.101; and 14 CFR 11.28 and 49.

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 Cessna Model 208B airplanes modified 
by the Soloy Corporation.
    1. Propulsion System.
    (a) Engine Requirements. The propulsion system must comply with the 
Soloy Corporation Soloy Dual Pac Engine Special Conditions (Docket No. 
93-ANE-14; No. 33-ANE-01), published in Federal Register, Volume 62, 
Number 33, dated February 19, 1997.
    (b) Engine Rotor Failure. In addition to showing compliance with 
23.903(b)(1) (Amendment 23-40), compliance must be shown with the 
following:
    (1) The engine type to be installed must be shown to have 
demonstrated a minimum of ten million hours of actual service 
experience in installations of equivalent or higher disk rotation 
loading without an uncontained high energy rotor failure; and a shield 
capable of preventing all fragments of an energy level that have been 
released during uncontained engine failures experienced in service from 
impacting the adjacent engine must be installed; and
    (2) It must be shown that the adjacent engine is not affected 
following any expected engine failure.
    (c) Engine case Burn-Through. In addition to showing compliance 
with Sec. 23.903(b)(1) (Amendment 23-40), the engine type to be 
installed must be shown to have demonstrated a minimum of ten million 
hours of actual service experience in installations of equivalent or 
higher combustor pressures and temperatures without an engine case 
burn-through event; or a firewall capable of containing a fire 
originating in the engine that burns through the engine case must be 
installed between the engines.
    (d) Propulsion System Function and Reliability Testing. The 
applicant must complete the testing required by Sec. 21.35(f)(1) 
(Amendment 21-51).
    2. Propeller Installation.
    (a) The applicant must complete a 2,500 airplane cycle evaluation 
of the propeller installation. This evaluation may be accomplished on 
the airplane in a combination of ground and flight

[[Page 49372]]

cycles or on a ground test facility. If the testing is accomplished on 
a ground test facility, the test configuration must include sufficient 
interfacing system hardware to simulate the actual airplane 
installation, including the engines, propulsion drive system, and mount 
system.
    (b) Critical Parts. (1) The applicant must define the critical 
parts of the propeller assembly. Critical parts are those parts whose 
failure during ground or flight operation could cause a catastrophic 
effect to the airplane, including loss of the ability to produce 
controllable thrust. In addition, parts, of which failure or probable 
combinations of failures would result in a propeller unbalance greater 
than that defined under paragraph (c), are classified as critical 
parts.
    (2) The applicant must develop and implement a plan to ensure that 
the critical parts identified in paragraph (b)(1) are controlled during 
design, manufacture, and throughout their service life so that the risk 
of failure in service is minimized.
    (c) Propeller Unbalance. The applicant must define the maximum 
allowable propeller unbalance that will not cause damage to the 
engines, propulsion drive system, engine mounts, primary airframe 
structure, or to critical equipment that would jeopardize the continued 
safe flight and landing of the airplane. Furthermore, the degree of 
flight deck vibration caused by this unbalance condition must not 
jeopardize the crew's ability to continue to operate the airplane in a 
safe manner.
3. Propeller Control System.
    (a) The propeller control system must be independent of the turbine 
engines such that a failure in either turbine engine or an engine 
control system will not result in loss of propeller control.
    (b) The propeller control system must be designed so that the 
occurrence of any single failure or probable combination of failures in 
the system which would prevent the propulsion system from producing 
thrust at a level required to meet Sec. 23.53(b)(1)(ii) (Amendment 23-
34) and Sec. 23.67(c) (Amendment 23-42) is extremely improbable.
    (c) The propeller control system must be designed to implement a 
default fixed-propeller pitch position in the event of a propeller 
control system failure:
    (1) A pitch change to the default fixed-pitch position must not 
exceed any limitation established as part of the engine and propeller 
type certificates;
4. Propulsion Instrumentation.
    (a) Engine Failure Indication. A positive means must be provided to 
indicate when an engine is no longer able to provide torque to the 
propeller. This means may consist of instrumentation required by other 
sections of part 23 or these special conditions if it is determined 
that those instruments will readily alert the flightcrew when an engine 
is no longer able to provide torque to the propeller.
    (b) Propulsion Drive System Instrumentation. In addition to the 
requirements of Sec. 23.1305 (Amendment 23-52), the following 
instruments must be provided for any power gearbox or transmission:
    (1) An oil pressure warning means and indicator for each pressure-
lubricated gearbox;
    (2) A low oil quantity indicator for each gearbox, if lubricant is 
self-contained;
    (3) An oil temperature indicator;
    (4) A tachometer for the propeller;
    (5) A torquemeter for the transmission driving a propeller shaft if 
the sum of the maximum torque that each engine is capable of producing 
exceeds the maximum torque for which the propulsion drive system has 
been certified under 14 CFR part 33; and
    (6) A chip detecting and indicating system for each gearbox.
5. Fire Protection System.
    (a) In addition to Sec. 23.1191(a) and (b) (not amended),
    (1) Each engine must be isolated from the other engine and the 
propulsion drive system by firewalls, shrouds, or equivalent means; and
    (2) Each firewall or shroud, including applicable portions of the 
engine cowling, must be constructed so that no hazardous quantity of 
liquid, gas, or flame can pass from the isolated compartment to the 
other engine or the propulsion drive system and so that firewall 
temperatures under all normal or failure conditions would not result in 
auto-ignition of flammable fluids and vapors present in the other 
engine and the propulsion drive system.
    (b) Components, lines, and fittings located in the engine and 
propulsion drive system compartments must be constructed of such 
materials and located at such distances from the firewall that they 
will not suffer damage sufficient to endanger the airplane if a fire is 
present in an adjacent engine compartment.
6. Airplane Performance.
    (a) In addition to Sec. 23.53(b)(1) (Amendment 23-34), the 
airplane, upon reaching a height of 50 feet above the takeoff surface 
level, must have reached a speed of not less than 1.3 VS1, 
or any lesser speed, not less than VX plus 4 knots, that is 
shown to be safe under all conditions, including turbulence and the 
propeller control system failed in any configuration that is not 
extremely improbable.
    (b) In lieu of Sec. 23.67(c)(1) (Amendment 23-42), the steady climb 
gradient must be determined at each weight, altitude, and ambient 
temperature within the operational limits established by the applicant, 
with the airplane in the following configurations:
    (1) Critical engine inoperative, remaining engine at not more than 
maximum continuous power or thrust, wing flaps in the most favorable 
position, and means for controlling the engine cooling air supply in 
the position used in the engine cooling tests required by Sec. 23.1041 
(Amendment 23-7) through Sec. 23.1045 (Amendment 23-7);
    (2) Both engines operating normally and the propeller control 
system failed in any configuration that is not extremely improbable, 
the engines at not more than maximum continuous power or thrust, wing 
flaps in the most favorable position, and means for controlling the 
engine cooling air supply in the position used in the engine cooling 
tests required by Sec. 23.1041 (Amendment 23-7) through Sec. 23.1045 
(Amendment 23-7).
    (c) Enroute climb/descent.
    (1) Compliance to Sec. 23.69(a) (Amendment 23-50) must be shown.
    (2) The steady gradient and rate of climb/descent must be 
determined at each weight, altitude, and ambient temperature within the 
operational limits established by the applicant with--
    (i) The critical engine inoperative, the engines at not more than 
maximum continuous power, the wing flaps retracted, and a climb speed 
not less than 1.2 VS1.
    (ii) Both engines operating normally and the propeller control 
system failed in any configuration that is not extremely improbable, 
the engines at not more than maximum continuous power, the wing flaps 
retracted, and a climb speed not less than 1.2 VS1.
    (d) In addition to Sec. 23.75 (Amendment 23-42), the horizontal 
distance necessary to land and come to a complete stop from a point 50 
feet above the landing surface must be determined as required in 
Sec. 23.75 (Amendment 23-42) with both engines operating normally and 
the propeller control system failed in any configuration that is not 
extremely improbable.
7. Airspeed Indicator.
    In lieu of the requirements of Sec. 23.1545(b)(5) (Amendment 23-
23), for one--engine inoperative or the propeller control system failed 
in any configuration that

[[Page 49373]]

is not extremely improbable, whichever is most critical, the best rate 
of climb speed VY, must be identified with a blue sector 
extending from the VY speed at sea level to the 
VY speed at an altitude of 5,000 feet, if VY is 
less than 100 feet per minute, or the highest 1,000-foot altitude (at 
or above 5,000 feet) at which the VY is 100 feet per minute 
or more. Each side of the sector must be labeled to show the altitude 
for the corresponding VY.
    8. Airplane Flight Manual. (a) In addition to the requirements of 
Sec. 23.1585(c) (Amendment 23-34), the following information must be 
included in the Airplane Flight Manual (AFM):
    (1) Procedures for maintaining or recovering control of the 
airplane at speeds above and below VS1 with the propeller 
control system failed in any configuration that is not extremely 
improbable.
    (2) Procedures for making a landing with the propeller control 
system failed in any configuration that is not extremely improbable and 
procedures for making a go-around with the propeller control system 
failed in any configuration that is not extremely improbable, if this 
latter maneuver can be performed safely; otherwise, a warning against 
attempting the maneuver.
    (3) Procedures for obtaining the best performance with the 
propeller control system failed in any configuration that is not 
extremely improbable, including the effects of the airplane 
configuration.
    (b) In lieu of the requirements of Sec. 23.1587 (c)(2) and (c)(4) 
(Amendment 23-39), the following information must be furnished in the 
Airplane Flight Manual:
    (1) The best rate-of-climb speed or the minimum rate-of-descent 
speed with one engine inoperative or the propeller control system 
failed in any configuration that is not extremely improbable, whichever 
is more critical.
    (2) The steady rate or gradient of climb determined in Special 
Condition #6, Airplane Performance, paragraph (b)(1) or paragraph 
(b)(2), whichever is more critical, and the airspeed, power, and 
airplane configuration.
    (c) The steady rate and gradient of climb determined in Special 
Condition #6, Airplane Performance, paragraph (c), must be furnished in 
the Airplane Flight Manual.
    (d) The landing distance determined under Sec. 23.75 (Amendment 23-
42) or in Special Condition #6, Airplane Performance, paragraph (d) of 
these proposed special conditions, whichever is more critical.

    Issued in Kansas City, Missouri on August 27, 1999.
Michael Gallagher,
Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. 99-23721 Filed 9-10-99; 8:45 am]
BILLING CODE 4910-13-P