[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
