[Federal Register Volume 80, Number 236 (Wednesday, December 9, 2015)]
[Rules and Regulations]
[Pages 76379-76381]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2015-31058]



Federal Aviation Administration

14 CFR Part 23

[Docket No. FAA-2015-3464; Special Conditions No. 23-272-SC]

Special Conditions: Cirrus Aircraft Corporation, SF50; Auto 

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.


SUMMARY: These special conditions are issued for the Cirrus Aircraft 
Corporation Model SF50 airplane. This airplane will have a novel or 
unusual design feature(s) associated with installation of an Auto 
Throttle System. 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 December 9, 
2015 and are applicable on December 2, 2015.

FOR FURTHER INFORMATION CONTACT: Jeff Pretz, Regulations and Policy 
Branch, ACE-111, Federal Aviation Administration, Small Airplane 
Directorate, Aircraft Certification Service, ACE-111, 901 Locust, Room 
301, Kansas City, MO 64106; telephone (816) 329-3239, facsimile (816) 



    On September 9, 2008, Cirrus Aircraft Corporation applied for a 
type certificate for their new Model SF50. On December 11, 2012 Cirrus 
elected to adjust the certification basis of the SF50 to include 14 CFR 
part 23 through amendment 62. The SF50 is a low-wing, 7-seat (5 adults 
and 2 children), pressurized, retractable gear, carbon composite 
airplane with one turbofan engine mounted partially in the upper aft 
fuselage. It is constructed largely of carbon and fiberglass composite 
materials. Like other Cirrus products, the SF50 includes a 
ballistically deployed airframe parachute. The SF50 has a maximum 
operating altitude of 28,000 feet and the maximum takeoff weight will 
be at or below 6,000 pounds with a range at economy cruise of roughly 
1,000 nautical miles.
    Current part 23 airworthiness regulations do not contain 
appropriate safety standards for an Auto Throttle System (ATS) 
installation; therefore, special conditions are required to establish 
an acceptable level of safety. Part 25 regulations contain appropriate 
safety standards for these systems, making the intent for this project 
to apply the language in Sec.  25.1329 for the auto throttle, while 
substituting Sec.  23.1309 and Sec.  23.143 in place of the similar 
part 25 regulations referenced in Sec.  25.1329. In addition, 
malfunction of the ATS to perform its intended function shall be 
evaluated per the Loss of Thrust Control (LOTC) criteria established 
under part 33 for electronic engine controls. An analysis must show 
that no single failure or malfunction or probable combinations of 
failures of the ATS will permit the LOTC probability to exceed those 
established under part 33 for an electronic engine control.

Type Certification Basis

    Under the provisions of 14 CFR 21.17, Cirrus must show that the 
Model SF50 meets the applicable provisions of part 23, as amended by 
amendments 23-1 through 23-62 thereto.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 23) do not contain adequate or 
appropriate safety standards for the SF50 because of a novel or unusual 
design feature, special conditions are prescribed under the provisions 
of Sec.  21.16.
    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 or similar 
novel or unusual design feature, the special conditions would also 
apply to the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the 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 14 CFR 11.19, in 
accordance with Sec.  11.38, and they become part of the type-
certification basis under Sec.  21.17(a)(2).

Novel or Unusual Design Features

    The SF50 will incorporate the following novel or unusual design 
features: An ATS as part of the automatic flight control system. The 
ATS utilizes a Garmin ``smart'' autopilot servo with a physical 
connection to the throttle quadrant control linkage. The auto throttle 
may be controlled by the pilot with an optional auto throttle control 
panel adjacent to the throttle lever. The auto throttle also provides 
an envelope protection function which does not require installation of 
the optional control panel.


    Part 23 currently does not sufficiently address auto throttle (also 
referred to as auto thrust) technology and safety concerns. Therefore, 
special conditions must be developed and applied to this project to 
ensure an acceptable level of safety has been obtained. For approval to 
use the ATS during flight, the SF50 must demonstrate compliance to the 
intent of the requirements of Sec.  25.1329,

[[Page 76380]]

applying the appropriate part 23 references to Sec.  23.1309 (to 
include performing a functional hazard assessment or system safety 
assessment to determine the applicable Software and Airborne Electronic 
Hardware assurance levels, and compliance to DO-178C & DO-254, as 
required) and Sec.  23.143.
    In addition, a malfunction of the ATS to perform its intended 
function is an LOTC event, and may result in a total loss of thrust 
control, transients, or uncommanded thrust changes. The classification 
of the failure condition for an LOTC event on a Class II single-engine 
aircraft is hazardous for aircraft that stall at or below 61 knots. 
From publication AC 23.1309-1E, based upon failure probability values 
shown in Figure 2, an LOTC event would have to meet a probability of 
failure value not to exceed 1 x 10-6. In-service data for 
LOTC in single-engine turbine aircraft shows LOTC events exceed this 
probability; therefore, part 33 requirements for engine control 
probabilities will be accepted for the part 23 LOTC requirement.
    The probabilities of failure for an LOTC event on a turbine engine 
shall not exceed the following (see AC33.28-1 and ANE-1993-33.28TLD-R1 
for further guidance):

1. Average Events per Million Hours: 10 (1x10-05 per 
2. Maximum Events per Million Hours: 100 (1x10-04 per 

    Note:  The maximum events per flight hour are intended for Time 
Limited Dispatch (TLD) operation where the risk exposure is 
mitigated by limiting the time in which the aircraft is operated in 
the degraded condition.

Discussion of Comments

    Notice of proposed special conditions No. 23-15-04-SC for the 
Cirrus Aircraft Corporation Model SF50 airplanes was published in the 
Federal Register on August 21, 2015 (80 FR 50808). No comments were 
received, and the special conditions are adopted as proposed.


    As discussed above, these special conditions are applicable to the 
Model SF50. Should Cirrus 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.
    Under standard practice, the effective date of final special 
conditions would be 30 days after the date of publication in the 
Federal Register; however, as the certification date for the Cirrus 
Aircraft Corporation Model SF50 airplane is imminent, the FAA finds 
that good cause exists to make these special conditions effective upon 


    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.


    The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704, 14 CFR 
21.16 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 Aircraft Corporation Model SF50 

1. Certification of Auto Throttle System Under Part 23

    a. Quick disengagement controls for the auto thrust functions must 
be provided for each pilot. The auto thrust quick disengagement 
controls must be located on the thrust control levers. Quick 
disengagement controls must be readily accessible to each pilot while 
operating the thrust control levers.
    b. The effects of a failure of the system to disengage the auto 
thrust functions when manually commanded by the pilot must be assessed 
in accordance with the requirements of Sec.  23.1309.
    c. Engagement or switching of the flight guidance system, a mode, 
or a sensor may not cause the auto thrust system to affect a transient 
response that alters the airplane's flight path any greater than a 
minor transient, as defined in paragraph (l)(1) of this section.
    d. Under normal conditions, the disengagement of any automatic 
control function of a flight guidance system may not cause a transient 
response of the airplane's flight path any greater than a minor 
    e. Under rare normal and non-normal conditions, disengagement of 
any automatic control function of a flight guidance system may not 
result in a transient any greater than a significant transient, as 
defined in paragraph (l)(2) of this section.
    f. The function and direction of motion of each command reference 
control, such as heading select or vertical speed, must be plainly 
indicated on, or adjacent to, each control if necessary to prevent 
inappropriate use or confusion.
    g. Under any condition of flight appropriate to its use, the flight 
guidance system may not produce hazardous loads on the airplane, nor 
create hazardous deviations in the flight path. This applies to both 
fault-free operation and in the event of a malfunction, and assumes 
that the pilot begins corrective action within a reasonable period of 
    h. When the flight guidance system is in use, a means must be 
provided to avoid excursions beyond an acceptable margin from the speed 
range of the normal flight envelope. If the airplane experiences an 
excursion outside this range, a means must be provided to prevent the 
flight guidance system from providing guidance or control to an unsafe 
    i. The flight guidance system functions, controls, indications, and 
alerts must be designed to minimize flight crew errors and confusion 
concerning the behavior and operation of the flight guidance system. 
Means must be provided to indicate the current mode of operation, 
including any armed modes, transitions, and reversions. Selector switch 
position is not an acceptable means of indication. The controls and 
indications must be grouped and presented in a logical and consistent 
manner. The indications must be visible to each pilot under all 
expected lighting conditions.
    j. Following disengagement of the auto thrust function, a caution 
(visual and auditory) must be provided to each pilot.
    k. During auto thrust operation, it must be possible for the flight 
crew to move the thrust levers without requiring excessive force. The 
auto thrust may not create a potential hazard when the flight crew 
applies an override force to the thrust levers.
    l. For purposes of this section, a transient is a disturbance in 
the control or flight path of the airplane that is not consistent with 
response to flight crew inputs or environmental conditions.
    (1) A minor transient would not significantly reduce safety margins 
and would involve flight crew actions that are well within their 
capabilities. A minor transient may involve a slight increase in flight 
crew workload or some physical discomfort to passengers or cabin crew.
    (2) A significant transient may lead to a significant reduction in 

[[Page 76381]]

margins, an increase in flight crew workload, discomfort to the flight 
crew, or physical distress to the passengers or cabin crew, possibly 
including non-fatal injuries. Significant transients do not require, in 
order to remain within or recover to the normal flight envelope, any of 
the following:
    i. Exceptional piloting skill, alertness, or strength.
    ii. Forces applied by the pilot which are greater than those 
specified in Sec.  23.143(c).
    iii. Accelerations or attitudes in the airplane that might result 
in further hazard to secured or non-secured occupants.
    It must also be demonstrated, through tests and analysis, that no 
single failure or malfunction or probable combinations of failures of 
the auto thrust system components results in the probability for LOTC, 
or un-commanded thrust changes and transients that result in an LOTC 
event, to exceed the following:

(1) Average Events per Million Hours: 10 (1x10-05 per 
(2) Maximum Events per Million Hours: 100 (1x10-04 per 

    Note:  The term ``probable'' in the context of ``probable 
combination of failures'' does not have the same meaning as used for 
a safety assessment process. The term ``probable'' in ``probable 
combination of failures'' means ``foreseeable,'' or those failure 
conditions anticipated to occur one or more times during the 
operational life of each airplane.

    Issued in Kansas City, Missouri, on December 2, 2015.
Patrick Mullen,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
[FR Doc. 2015-31058 Filed 12-8-15; 8:45 am]