Special Conditions: Cirrus Design Corporation, Model SF50; Fire Extinguishing for Upper Aft Fuselage Mounted Engine, 20516-20518 [2010-9026]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 75, Number 75 (Tuesday, April 20, 2010)]
[Rules and Regulations]
[Pages 20516-20518]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-9026]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 23

[Docket No. CE305; Special Conditions No. 23-245-SC]


Special Conditions: Cirrus Design Corporation, Model SF50; Fire 
Extinguishing for Upper Aft Fuselage Mounted Engine

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions; request for comments.

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SUMMARY: These special conditions are issued for the Cirrus Design 
Corporation, model SF50 airplane. This single turbofan engine airplane 
will have a novel or unusual design feature(s) associated with mounting 
the engine in the aft fuselage. 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.

DATES: The effective date of these special conditions is April 12, 
2010.
    We must receive your comments by May 20, 2010.

ADDRESSES: Mail two copies of your comments to: Federal Aviation 
Administration, Regional Counsel, ACE-7, Attn: Rules Docket No. CE305, 
901 Locust, Kansas City, MO 64106. You may deliver two copies to the 
Regional Counsel at the above address. Mark your comments: Docket No. 
CE305. You may inspect comments in the Rules Docket weekdays, except 
Federal holidays, between 7:30 a.m. and 4 p.m.

FOR FURTHER INFORMATION CONTACT: Leslie B. Taylor, Federal Aviation 
Administration, Small Airplane Directorate, Aircraft Certification 
Service, 901 Locust, Room 301, Kansas City, MO 64106; telephone (816) 
329-4134; facsimile (816) 329-4090, email leslie.b.taylor@faa.gov.

SUPPLEMENTARY INFORMATION: The FAA has determined that notice and 
opportunity for prior public comment hereon are impracticable because 
these procedures would significantly delay issuance of the design 
approval and thus delivery of the affected aircraft. In addition, the 
substance of these special conditions has been subject to the public 
comment process in several prior instances with no substantive comments 
received. The FAA therefore finds that good cause exists for making 
these special conditions effective upon issuance.

Comments Invited

    We invite interested persons to submit such written data, views, or 
arguments as they desire. The most helpful comments reference a 
specific portion of the special conditions, explain the reason for any 
recommended change, and include supporting data. We ask that you send 
us two copies of written comments.
    We will file in the docket all comments we receive, as well as a 
report summarizing each substantive public contact with FAA personnel 
about these special conditions. You may inspect the docket before and 
after the comment closing date. If you wish to review the docket in 
person, go to the address in the ADDRESSES section of this preamble 
between 7:30 a.m. and 4 p.m., Monday through Friday, except Federal 
holidays.
    We will consider all comments we receive by the closing date for 
comments. We will consider comments filed late if it is possible to do 
so without incurring expense or delay. We may change these special 
conditions based on the comments we receive.
    If you want us to let you know we received your comments on these 
special conditions, send us a pre-addressed, stamped postcard on which 
the docket number appears. We will stamp the date on the postcard and 
mail it back to you.

Background

    On September 9, 2008, Cirrus Design Corporation applied for a type 
certificate for their new model SF50. The model SF50 is a 7 seat (5 
adults and 2 children), pressurized, retractable gear, carbon 
composite, airplane with one turbofan engine mounted partially in the 
upper aft fuselage.
    The single turbofan engine is mounted on the upper aft fuselage, 
not in the pilot's line of site. Upper aft fuselage mounted engine 
installations, along with the need to protect such installed engines 
from fires, were not envisioned in the development of the part 23 
normal category regulations.

[[Page 20517]]

Type Certification Basis

    Under the provisions of 14 CFR 21.17, Cirrus Design Corporation 
must show that the model SF50 meets the applicable provisions of part 
23, as amended by Amendment 23-1 through Amendment 23-59 thereto.
    If the Administrator finds that the applicable airworthiness 
regulations, part 23, do not contain adequate or appropriate safety 
standards for the model SF50 because of a novel or unusual design 
feature, special conditions are prescribed under the provisions of 
Sec.  21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the model SF50 must comply with the fuel vent and exhaust 
emission requirements of 14 CFR part 34 and the noise certification 
requirements of 14 CFR part 36; and the FAA must issue a finding of 
regulatory adequacy under section 611 of Public Law 92-574, the ``Noise 
Control Act of 1972.''
    The FAA issues special conditions, as defined in Sec.  11.19, under 
Sec.  11.38 and they become part of the type certification basis under 
Sec.  21.17(a)(2).
    Special conditions are initially applicable to the model for which 
they are issued. Should the type certificate for that model be amended 
later to include any other model that incorporates the same novel or 
unusual design feature, the special conditions would also apply to the 
other model.

Novel or Unusual Design Features

    The model SF50 will incorporate the following novel or unusual 
design features: An aft fuselage mounted engine is not in the pilot's 
line of sight. This type of configuration was not envisioned in the 
development of part 23 normal category airplanes. Therefore, a special 
condition for the fire extinguishing system for the engine on the model 
SF50 is required.
    Regulations requiring and defining engine compartment fire 
extinguishing systems already exist for part 23 commuter category 
airplanes. These regulations will provide an adequate level of safety 
for the normal category model SF50 with the aft mounted engine except 
SC 23.1195 will require a two shot system.
    As the extinguishing agent is subject to change during the service 
life of the airplane, the certification basis must include 14 CFR 
23.1197, 23.1199, 23.1201 in their entirety.

Discussion

    Part 23 has historically addressed fire protection through 
prevention, identification, and containment. Prevention has been 
accomplished by minimizing the potential for ignition of flammable 
fluids and vapors. Identification has traditionally been achieved by 
the location of the engines within the pilot's primary field of view 
and/or with the incorporation of fire detection systems. This 
philosophy has provided for both the rapid detection of a fire and 
confirmation when it has been extinguished. Containment has been 
provided through the isolation of designated fire zones through 
flammable fluid shutoff valves and firewalls. The containment 
philosophy also ensures that components of the engine control system 
will function effectively to permit a safe shutdown of the engine. 
However, containment has only been required to be demonstrated for 15 
minutes. In the event of a fire in a traditional part 23 airplane, the 
corrective action is to land as soon as possible. For a small, simple 
aircraft originally envisioned by part 23, it is possible to descend 
the aircraft to a suitable landing site within 15 minutes. Thus, if the 
isolation means do not extinguish the fire, the occupants can safely 
exit the aircraft prior to the firewall being breached. These simple 
and traditional aircraft normally have the engine located away from 
critical flight control systems and primary structure. This has ensured 
that throughout the fire event the pilot can maintain control and 
continue safe flight. It has also made predicting the effects of a fire 
relatively easy. Other design features of these simple and traditional 
aircraft, such as low stall speeds and short landing distances, ensure 
that even in the event of an off field landing the potential for a 
catastrophic outcome has been minimized.
    Excluding commuter category, normal category airplanes 
incorporating one or more engines on the aft fuselage were not 
envisioned in part 23. Engine(s) located on the aft fuselage offer 
minimal opportunity to visually detect a fire. The ability to 
extinguish an engine fire becomes extremely critical due to this 
location. In a traditional pylon engine there is a standoff distance 
from the fuselage where there is no possible impingement of fluid or 
flame on the fuselage. Thus after 5 minutes if the fluid lines succumb 
to the fire any liberated fluid would not come into contact with any 
other critical structure or the fuselage. In essence the engine could 
burn off of the pylon and not adversely compromise the fuselage. The 
Cirrus design configuration does not benefit from this consideration 
and thus there is a greater risk due to fire. Also, if there was a fire 
due to a buildup of fuel in the exhaust nozzle a low velocity flame 
could impinge upon the fuselage or empennage.
    Airplanes of the classic configuration with twin aft pylon mounted 
engines have fire extinguishing ``one-shot'' systems. A two shot system 
is necessary for fuselage embedded engines since the metallic 
components in the fire zone can be hot enough to re-ignite flammable 
fumes after the first fire has been extinguished. The consequences of a 
fire in these locations can be more varied, adverse, and difficult to 
predict than the engine fire envisioned for a typical part 23 airplane. 
The Cirrus aft engine installation is more indicative of an embedded 
engine rather than a pylon mounted engine.

Applicability

    As discussed above, these special conditions are applicable to the 
model SF50. Should Cirrus Design Corporation apply at a later date for 
a change to the type certificate to include another model incorporating 
the same novel or unusual design feature, the special conditions would 
apply to that model as well.

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 affects only the applicant who applied to the FAA for approval of 
these features on the airplane.
    The substance of these special conditions has been subjected to the 
notice and comment period in several prior instances and has been 
derived without substantive change from those previously issued. It is 
unlikely that prior public comment would result in a significant change 
from the substance contained herein. Therefore, because a delay would 
significantly affect the certification of the airplane, which is 
imminent, the FAA has determined that prior public notice and comment 
are unnecessary and impracticable, and good cause exists for adopting 
these special conditions upon issuance. The FAA is requesting comments 
to allow interested persons to submit views that may not have been 
submitted in response to the prior opportunities for comment described 
above.

List of Subjects in 14 CFR Part 23

    Aircraft, Aviation safety, Signs and symbols.

[[Page 20518]]

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 
21.17; and 14 CFR 11.38 and 11.19.

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 Cirrus Design Corporation model SF50 
airplanes.

Fire Extinguishing for Upper Aft Fuselage Mounted Engine

SC 23.1195 Fire Extinguishing Systems

    Fire extinguishing systems must be installed and compliance shown 
with the following:
    (a) Except for combustor, turbine, and tailpipe sections of 
turbine-engine installations that contain lines or components carrying 
flammable fluids or gases for which a fire originating in these 
sections is shown to be controllable, a fire extinguisher system must 
serve each engine compartment.
    (b) The fire extinguishing system, the quantity of the 
extinguishing agent, the rate of discharge, and the discharge 
distribution must be adequate to extinguish fires. An individual ``two 
shot'' system must be used.
    (c) The fire extinguishing system for a nacelle must be able to 
simultaneously protect each compartment of the nacelle for which 
protection is provided.

SC 23.1197 Fire Extinguishing Agents

    The following applies:
    (a) Fire extinguishing agents must--
    (1) Be capable of extinguishing flames emanating from any burning 
of fluids or other combustible materials in the area protected by the 
fire extinguishing system; and
    (2) Have thermal stability over the temperature range likely to be 
experienced in the compartment in which they are stored.
    (b) If any toxic extinguishing agent is used, provisions must be 
made to prevent harmful concentrations of fluid or fluid vapors (from 
leakage during normal operation of the airplane or as a result of 
discharging the fire extinguisher on the ground or in flight) from 
entering any personnel compartment, even though a defect may exist in 
the extinguishing system. This must be shown by test except for built-
in carbon dioxide fuselage compartment fire extinguishing systems for 
which--
    (1) Five pounds or less of carbon dioxide will be discharged, under 
established fire control procedures, into any fuselage compartment; or
    (2) Protective breathing equipment is available for each flight 
member on flight deck duty.

SC 23.1199 Extinguishing Agent Containers

    The following applies:
    (a) Each extinguishing agent container must have a pressure relief 
valve to prevent bursting of the container by excessive internal 
pressures.
    (b) The discharge end of each discharge line from a pressure relief 
connection must be located so that discharge of the fire extinguishing 
agent would not damage the airplane. The line must also be located or 
protected to prevent clogging caused by ice or other foreign matter.
    (c) A means must be provided for each fire extinguishing agent 
container to indicate that the container has discharged or that the 
charging pressure is below the established minimum necessary for proper 
functioning.
    (d) The temperature of each container must be maintained under 
intended operating conditions to prevent the pressure in the container 
from --
    (1) Falling below that necessary to provide an adequate rate of 
discharge; or
    (2) Rising high enough to cause premature discharge.
    (e) If a pyrotechnic capsule is used to discharge the extinguishing 
agent, each container must be installed so that temperature conditions 
will not cause hazardous deterioration of the pyrotechnic capsule.

SC 23.1201 Fire Extinguishing System Materials

    The following apply:
    (a) No material in any fire extinguishing system may react 
chemically with any extinguishing agent so as to create a hazard.
    (b) Each system component in an engine compartment must be 
fireproof.

    Issued in Kansas City, Missouri on April 12, 2010.
Steve Thompson,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2010-9026 Filed 4-19-10; 8:45 am]
BILLING CODE 4910-13-P