# ~ 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 ofTransportation 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) SF50 aircraft project#TC6444CH-A. i ;

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Letter Log: 9447

Cirrus Design Corporation requests regulatory relief in the form ofan exemption to the requirements of 14 CFR §23.177(b) for Cirrus model SF50 aircraft Project Number TC6444CH-A.

The Cirrus Model SF50 is a single-engine, turbofan, low-wing, retractable gearaircraft. A somewhat atypical v-tail is its most unique feature. The primary flight control system is composed ofconventional 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 actuatorvia 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 meetthe requirements of§23.147(c), allowing continued safe flight in the event of primary lateral control system failure. During developmental flight testing, the SF50 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 ofseveral 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, ifyou wish, other contact information such as a fax number, telephone number, or e-mail address; Cirrus Design Corporation 4515 Taylor Circle Duluth, MN 55811Engelmann (CDC) to US DOT Page 2 of4

Additional contact information is provided atthe end ofthis letter. Log:9447 23 July 2014

§11.81(b) the specific section orsections of 14 CFRfrom 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 lateralstability, as shown bythe tendencyto raise the low wing in a sideslip with the aileron controls free, maynotbe negative foranylanding gearand flap position appropriate to the takeoff, climb, cruise, approach, andlanding configurations. This mustbe shown with symmetricalpowerfrom idle up to 75 percentofmaximum continuouspoweratspeeds from 1.2 Vs 1 in the takeoff configuration(s) andatspeeds from 1.3 Vs 1 in otherconfigurations up to the maximum allowable airspeedforthe configuration being investigated (VpE, VLE, VNo, VpcfMpc, whicheveris appropriate) in the takeoff, climb, cruise, descent, and approach configurations. Forthe landing configuration the powermustbe that necessary to maintain a 3-degree angle ofdescentin coordinatedflight. (2) The static lateralstabilitymaynotbe negative at 1.2 V 81 in the takeoff configuration, orat 1.3 V 81 in otherconfigurations. (3) The angle ofsideslip for these tests mustbe appropriate to the type ofairplane, butin no case may the constantheading sideslip angle be less than thatobtainable with 

### a 10 degree bankor, ifless, the maximum bankangle obtainable with full rudderdeflection or 150poundrudderforce.
§11.81(c) the extent of reliefyou seek, and the reason you seekthe relief; Cirrus Design Corporation requests this exemption to reduce the complexity ofthe 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 ofa 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 itwould benefitthe public as awhole; Granting this exemption is in the public interest by allowing simplerflight control rigging and easier maintenance without adversely affecting operational safety. The Rudder-Aileron interconnect (RAI) has been the subject ofat leasttwo service bulletins and an AD intended to assure proper rigging on previous Cirrus designed aircraftwith similarwing and tail feather design. Granting this exemption would allow operators to perform maintenance on a system of less complexity ofthe 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 howthe exemption would provide a level ofsafety at least equal to that provided by the rule from which you seekthe exemption;Engelmann (CDC) to US DOT Page 3 of4 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 ofthe 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 ofthis regulation is the same as that of §23.177(b), controllability with the loss ofthe primary control system. However, the currently accepted method for demonstrating compliance incorporates the use ofthe trim system ratherthan inherent aerodynamic stability. Demonstration requires establishing a zero rate ofdescent using only normal flight and power controls, without the use ofthe 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 ofthe exemption for the QuestAircraft 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. model7000amphibian floats on QuestAircraftDesign, LLCmodel 100 "Kodiak" aircraft is exempt from meetingthe static lateralstabilityrequirementof §23.177(b) -providedthe aircraft is equippedwith the Wipaire Emergency Trim Timer Override System (ETTOS). The ETTOSsystemprovides a level of safetyatleast equal to thatprovidedby§23.177(b).
The ETTOS is necessary in the case ofthe Kodiak §23.177(b) exemption, as it allows continuous operation ofthe 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 seekthe exemption; and (2) A brief description ofthe nature of the exemption you seek; The FAA may publish this letter in its entirety.
§11.81(g) any additional information, views orarguments available to supportyour request; Cirrus Design notes that the FAA granted an exemption to 14 CFR §23.177(b} for a QuestAircraft 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 SF50 easily overcome the weak negative static lateral instability using roll trim inputs.Engelmann (CDC) to US DOT Page 4 of4 Log:9447 23 July 2014 §11.81(h) ifyou want to exercise the privileges ofyour exemption outside the United States, the reason why you need to do so. This petition for exemption is for FAAtype certification purposes only. Thus, this item is not applicable forthe 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 numberTC6444CH-A) aircraft. This exemption would be in the public interest because it would allow removal ofthe RAI in these aircraft, reduce complexity ofthe flight control system, and relieve possible maintenance induced rigging errors thereby increasing safety ofthese aircraft. This conclusion is supported by flight tests showing compliance with the intent of 14 CFR §23.177(b). This exemption would not adversely affectthe level ofsafety 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