27 Feb., 20 15 U.S. Department of Transportation Docket Operations West Building Ground Floor, Room W1 2 - 140 1200 New Jersey Avenue, SE Washington, D.C. 20590 Subject: FAA Project T C6444 CH -A

– Petition for Stall Speed Exemption Log: 9737 Cirrus requests a n exemption to the stall speed requirement of 14 CFR §23.1419(a), Am dt. 43, as part of the flight in icing conditions ma jor type design change to the Cirrus Model S F50 . This type design change is open with the Chicago ACO under FAA project TC6444 CH -A . Th e exemption is requested since the S F50 will not meet the 61 - knot stall speed requirement with critical ice accretions. The following responses to the exemption information requirement of 14 CFR §11.81 use the guidance found in AC 23.1419 -2D, Para. 13.a.( c). **§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 Additional contact information is provided at the end of this letter. **§11.81(b) The specific section or sections of 14 CFR from which you seek an exemption;**  Cirrus seeks an exemption to 14 CFR §23.1419(a) with respect to the 61 - knot stall speed requirement of §23.49 (c) & (d)

. **§11.81(c) The extent o f relief you seek, and the reason you seek the relief;**  Specifically, Cirrus seeks an exemption to the following statement of 14 CFR §23.1419(a): “As used in this section, “Capable of operating safely,” means that airplane performance, controllability, ma neuverability, and stability must not be less than that required in part 23, subpart B.” This exemption is only requested with respect to the 61 - knot stall speed requirement of 14 CFR §23.49(c) & (d ) for the SF50

. T he non - contaminated stall speed of the SF 50 is above the 61 - knot rule, being at 65kias with the stick pusher at 67kias. T he SF50 with critical ice accretions will not cause these num bers to be even higher . Thus, this exemption has been requested as described in the FAA guidance provided in AC 23 .1419 -2D, Para. 13.a.(c).**Engelmann (**  **CDC) to US DOT**  **Log: 9737**  **Page 2**  **of 4**  **27 Feb.**  **20 15**  This exemption is only requested for aircraft units receiving an initial standard certificate of airworthiness subsequent to the type design certified by FAA project T C6444 CH -A. **§11.81(d) The reasons why granting your request wo uld be in the public interest;**  **that is, how it would benefit the public as a whole;** The SF50 is primarily used for cross- country travel and has a high probability of encountering inclement weather

– including icing conditions . Increasing the flight envelo pe of the SF50 to include flight in icing conditions provides a significant increase in safety for SF50 operators
– especially those who inadvertently encounter icing conditions

. The associated design features required to make flight in icing operations possible add s a significant level of redundancy and increased system capability over the existing design. Also , the flight testing required for this design change will fully prove out the capability of this system and shown that operational safety will have been increased

. Thus, granting this exemption would be in the public interest due to the increased safety associated with the operational envelope expansion without negatively impacting aircraft utility. **§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;**  The following compensating features, as described in AC 23.1419 -2D, will ensure the level of safety will not be adversely affected by this exemption. 1 . The airplane with critical ice accretions as defined in paragraph 13.b. of this AC com plies with the stall warning requirements of §23.207. The SF50 ma intain s the required stall margin and doe s not cause nuisance warnings as required by §23.207. This will be shown by flight test and documented in the flight test reports submitted to the FAA

. 2 . The AFM performance data in icing conditions reflects the higher stall and operating speeds. The AFM supplement for flight in icing equipped airplanes includes the performance data to be used when flying in icing conditions and/or with known aircraft ice accretions. These speeds have been determined by flight test and documented in the flight test reports submitted to the FAA

. 3

. The airplane with critical ice accretions has acceptable stall characteristics and is safely controllable with normal piloting skill as required by §23.201 and §23.203. F light testing with simulated critical ice accretions was a ccomplished showing acceptable stall characteristics as required by §23.201 and §23.203 and accounting for normal piloting skill as required by §23.141. This was documented in the flight test reports submitted to the FAA

.**Engelmann (**  **CDC) to US DOT**  **Log: 9737**  **Page 3**  **of 4**  **27 Feb.**  **20 15**  4 . The tire requirements of §23.7 33 and brake requirements of §23.735 are met with the higher stall and operating speeds. Cirrus has show n that the existing tires and brake system will meet the requirements of §23.733 and §23.735, respectively. This was shown by analysis and documented i n the design report submitted to the FAA

. 5 . The ground handling requirements of §23.231 , §23.233 and §23.235 are met with higher landing speeds. Cirrus conducted ground handling tests during the simulated ice shape flight tests and found no adverse handli ng characteristics

. 6 . All other airplane s ystem or testing requirements that could be affected by higher operating speeds, such as autopilot and flight director gains are evaluated. The autopilot and flight director were evaluated during the flight test p rogram and documented in the natural icing flight test report submitted to the FAA

. 7 . Each seat/restraint system would have to include a safety belt an d shoulder harness with a metal -to- metal latching device. The SF50 utilizes a seat restraint system th at includes safety belts and shoulder harnesses with metal -to- metal latching devices for all seven pilot / occupant seats. 8 . The airplane certification basis would have to include §23.1091 at amendment 23 - 51 and §23.1093 at amendment 23 - 51 to provide the latest regulations for engine operation in icing conditions. The certification basis for the SF50 was established at amendment 23 -62 and includes §23.1091 and §23.1093 at amendment 23 - 51. Compliance for each of these regulations will be addressed as part of this type certification project and documented in the design report submitted to the FAA

. 9 . The airplane certification basis would have to include §23.995 at amendment 23 -29. The certification basis for the SF50 was established at amendment 23 -62 and includes §23.995 at amendment 23 - 29. The existing compliance shown for this regulation was not affected by this type design change. **§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 )**  **An y additional information, views or arguments available to support your**  **request;** In addition to the compensating safety features dis cussed for §11.81(e) above, Cirrus will be providing a training module specific to flight in icing conditions that will include training related to increased stall speeds associated with airframe ice accretion. Cirrus has an**Engelmann (**  **CDC) to US DOT**  **Log: 9737**  **Page 4**  **of 4**  **27 Feb.**  **20 15**  excellent pilot training program that emphasizes operational safety. This module will be all SF50 airplanes. **§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 type certifi cation purposes only. Thus, this item is not applicable for the exemption described herein

. In conclusion, Cirrus requests the FAA grant an exemption to 14 CFR §23.1419(a) specific to the 61 - knot stall speed requirement. This exemption would be in the pu blic interest by providing increased safety in inclement weather without requiring a significant reduction in useful load. Fu rther, the level of safety will be maintained by complying the com pensating features as described in AC 23.1419 -2D. Sincerely, 

# Signed: Tom Engelmann To m Engelmann Lead , Airworthiness Phone: 218. 788.3 164 Fax: 218.529.7301 Em ail: tengelmann@cirrusaircraft.com Cc: Wesley Rouse, Chicago ACO