~ CIRRUS 

CIRRUS DESIGN 

CORPORATION 

4515 Taylor Circle 

Duluth, MN 55811 

OPERATIONS 

PHONE 218.727.2737 

FAX 218.727.2148 

SALES 

PHONE 218.788.3900 

FAX 218.788.3500 

www.cirrusdesign.com 

23 July 2014 

U.S. Department of Transportation 

Docket Operations 

West Building Ground Floor, Room W12-140 

1200 New Jersey Avenue, SE 

Washington, D.C. 20590 

Subject 

Petition for Exemption from 14 CFR §23.177(b) 

SF 50 aircraft project# TC6444CH-A. 

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Letter Log: 9447 

Cirrus Design Corporation requests regulatory relief in the form of an exemption to the 

requirements of 14 CFR §23.177(b) for Cirrus model SF50 aircraft Project Number 

TC6444CH-A. 

The Cirrus Model SF 50 is a single-engine, turbofan, low-wing, retractable gear aircraft. 

A somewhat atypical v-tail is its most unique feature. The primary flight control system 

is composed of conventional control surfaces with actuation achieved through push-pull 

tubes for pitch and roll, and cables for yaw. Roll control is achieved through ailerons, 

while pitch and yaw control are achieved through mixing ruddervator control inputs. 

Secondary flight controls include partial span wing flaps. 

Aileron trim control is achieved with a trim tab located on the LH aileron. The trim tab is 

connected to an electric actuator via push-pull tubes. In the event primary roll control is 

lost, aileron trim remains effective on the LH aileron. Additionally, the SF50 aileron trim 

system will meet the requirements of §23.147(c), allowing continued safe flight in the 

event of primary lateral control system failure. 

During developmental flight testing, the SF 50 flight test proof-of-concept vehicle 

demonstrated weakly divergent lateral stability in certain configurations. All other 

configurations demonstrated either neutral or positive lateral stability. 

On the SR20 and SR22 the rudder aileron interconnect introduced a higher level of 

complexity into the flight control system, and was the subject of several Service 

Bulletins as well as an Airworthiness Directive (AD) on the previous Cirrus Models 

SR20 and SR22. To avoid a similar happening on the SF50 Cirrus is requesting and 

exemption. 

An exemption is requested to simplify maintainability, by not designing in a RAI system, 

without having a detrimental effect on aircraft operational safety. 

The following is provided to fulfill the exemption information requirement of 14 CFR 

§11.81. 

§11.81 (a) your name and mailing address and, if you wish, other contact 

information such as a fax number, telephone number, or e-mail address; 

Cirrus Design Corporation 

4515 Taylor Circle 

Duluth, MN 55811 
Engelmann (CDC) to US DOT 

Page 2 of 4 

Additional contact information is provided at the end of this letter. 

Log:9447 

23 July 2014 

§11.81(b) the specific section or sections of 14 CFR from which you seek an 

exemption; 

Cirrus Design Corporation seeks an exemption from the Static Directional and Lateral 

Stability requirements expressed in 14 CFR §23.177(b). 

(1) The static lateral stability, as shown by the tendency to raise the low wing in a 

sideslip with the aileron controls free, may not be negative for any landing gear and 

flap position appropriate to the takeoff, climb, cruise, approach, and landing 

configurations. This must be shown with symmetrical power from idle up to 75 

percent of maximum continuous power at speeds from 1.2 Vs 1 in the takeoff 

configuration(s) and at speeds from 1.3 Vs 1 in other configurations up to the 

maximum allowable airspeed for the configuration being investigated (VpE, VLE, 

VNo, VpcfMpc, whichever is appropriate) in the takeoff, climb, cruise, descent, and 

approach configurations. For the landing configuration the power must be that 

necessary to maintain a 3-degree angle of descent in coordinated flight. 

(2) The static lateral stability may not be negative at 1.2 V81 in the takeoff 

configuration, or at 1.3 V81 in other configurations. 

(3) The angle of sideslip for these tests must be appropriate to the type of airplane, 

but in no case may the constant heading sideslip angle be less than that obtainable 

with a 10 degree bank or, if less, the maximum bank angle obtainable with full 

rudder deflection or 150 pound rudder force. 

§11.81 (c) the extent of relief you seek, and the reason you seek the relief; 

Cirrus Design Corporation requests this exemption to reduce the complexity of the flight 

control system by allowing the SF50 aircraft design to not include a Rudder-Aileron 

Interconnect (RAI). This will improve maintainability and reduce the possibility of a misrigged condition resulting from a maintenance action on a system that included an RAI. 

§11.81 (d) the reasons why granting your request would be in the public interest; 

that is, how it would benefit the public as a whole; 

Granting this exemption is in the public interest by allowing simpler flight control rigging 

and easier maintenance without adversely affecting operational safety. 

The Rudder-Aileron interconnect (RAI) has been the subject of at least two service 

bulletins and an AD intended to assure proper rigging on previous Cirrus designed 

aircraft with similar wing and tail feather design. Granting this exemption would allow 

operators to perform maintenance on a system of less complexity of the flight control 

system and relieve possible maintenance induced rigging errors thereby increasing 

operational safety. 

§11.81(e) the reasons why granting the exemption would not adversely affect 

safety, or how the exemption would provide a level of safety at least equal to that 

provided by the rule from which you seek the exemption; 
Engelmann (CDC) to US DOT 

Page 3 of 4 

Log:9447 

23 July 2014 

The Cirrus SF50 AFM will provide guidance stating that both primary rudder control and 

aileron trim should be used to control the airplane in the event of loss of primary aileron 

control. The aileron trim control is located on the primary control stick on the SF50 and 

moves in the same axis as the primary control. This provides for a more intuitive and 

natural backup to the primary roll control than does rudder pedal backup for primary 

yaw control. 

The FAA currently accepts use of the pitch trim system to show compliance to the 

requirements of §23.145(e) for longitudinal controllability in the event of loss of primary 

control. The intent of this regulation is the same as that of §23.177(b), controllability with 

the loss of the primary control system. However, the currently accepted method for 

demonstrating compliance incorporates the use of the trim system rather than inherent 

aerodynamic stability. Demonstration requires establishing a zero rate of descent using 

only normal flight and power controls, without the use of the primary longitudinal control 

system. 

Precedent- A similar method of satisfying the intent of §23.177(b) has been approved 

by the Small Airplane Directorate in the case of the exemption for the Quest Aircraft 

Design, LLC., Model 100 Kodiak aircraft on Wipaire model 7000 amphibian floats. In a 

letter dated May 25, 2010, exemption no. 10068 was granted, stating: 

Wipaire, Inc. model7000 amphibian floats on Quest Aircraft Design, LLC model 100 

"Kodiak" aircraft is exempt from meeting the static lateral stability requirement of 

§23.177 (b) -provided the aircraft is equipped with the Wipaire Emergency Trim Timer 

Override System (ETTOS). The ETTOS system provides a level of safety at least equal 

to that provided by§ 23.177(b). 

The ETTOS is necessary in the case of the Kodiak §23.177(b) exemption, as it allows 

continuous operation of the trim system. The Kodiak's standard system architecture 

incorporates built-in delays in trim system actuation. The Cirrus SF50 trim system 

functions immediately and continuously upon depressing the trim switch, thus 

eliminating the need for any trim system override. 

§11.81(f) a summary we can publish in the Federal Register, stating: (1) The rule 

from which you seek the exemption; and (2) A brief description of the nature of 

the exemption you seek; 

The FAA may publish this letter in its entirety. 

§11.81(g) any additional information, views or arguments available to support your 

request; 

Cirrus Design notes that the FAA granted an exemption to 14 CFR §23.177(b} for a 

Quest Aircraft Design Model 100 "Kodiak" aircraft in order to install Wipaire Model 7000 

floats. The Kodiak exhibited a weak low speed lateral instability with the ailerons free 

which was correctable by use of roll trim. 

Cirrus Design pilots flying the SF 50 easily overcome the weak negative static lateral 

instability using roll trim inputs. 
Engelmann (CDC) to US DOT 

Page 4 of 4 

Log:9447 

23 July 2014 

§11.81 (h) if you want to exercise the privileges of your exemption outside the 

United States, the reason why you need to do so. 

This petition for exemption is for FAA type certification purposes only. Thus, this item is 

not applicable for the exemption described herein. 

In conclusion, 

Cirrus Design Corporation requests an exemption to the requirements prescribed in 14 

CFR §23.177(b) for the SF50 (Project number TC6444CH-A) aircraft. This exemption 

would be in the public interest because it would allow removal of the RAI in these 

aircraft, reduce complexity of the flight control system, and relieve possible maintenance 

induced rigging errors thereby increasing safety of these aircraft. This conclusion is 

supported by flight tests showing compliance with the intent of 14 CFR §23.177(b). This 

exemption would not adversely affect the level of safety provided in the existing 

regulations. 

Sincerely, 

Tom Engelmann 

Certification Engineer, Cirrus Aircraft 

Phone: 218.788.3164 

Fax: 218.529.7301 

Email: tengelmann@cirrusdesign.com 

Cc: Wesley Rouse, Chicago AGO