27 Feb., 2015

U.S. Department of Transportation

Docket Operations

West Building Ground Floor, Room W12-140

1200 New Jersey Avenue, SE

Washington, D.C. 20590

Subject: FAA Project TC6444CH-A – Petition for Stall Speed Exemption Log: 9737

Cirrus requests an exemption to the stall speed requirement of 14 CFR §23.1419(a), 

Amdt. 43, as part of the flight in icing conditions major type design change to the Cirrus 

Model SF50. This type design change is open with the Chicago ACO under FAA project 

TC6444CH-A. The exemption is requested since the SF50 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 of 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, maneuverability, 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.

The non-contaminated stall speed of the SF50 is above the 61-knot rule, being at 65kias 

with the stick pusher at 67kias. The SF50 with critical ice accretions will not cause these 

numbers 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).
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This exemption is only requested for aircraft units receiving an initial standard certificate of 

airworthiness subsequent to the type design certified by FAA project TC6444CH-A. 

§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;

The SF50 is primarily used for cross-country travel and has a high probability of 

encountering inclement weather – including icing conditions. Increasing the flight 

envelope 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 adds 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 

complies with the stall warning requirements of §23.207.

The SF50 maintains the required stall margin and does 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.

Flight testing with simulated critical ice accretions was accomplished 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.
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4. The tire requirements of §23.733 and brake requirements of §23.735 are met with the 

higher stall and operating speeds.

Cirrus has shown 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 in 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 handling characteristics.

6. All other airplane system 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 program 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 and shoulder harness 

with a metal-to-metal latching device.

The SF50 utilizes a seat restraint system that 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) Any additional information, views or arguments available to support your 

request;

In addition to the compensating safety features discussed 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 
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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 certification 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 public 

interest by providing increased safety in inclement weather without requiring a significant 

reduction in useful load. Further, the level of safety will be maintained by complying the 

compensating features as described in AC 23.1419-2D.

Sincerely, 

Signed: Tom Engelmann

Tom Engelmann

Lead, Airworthiness

Phone: 218.788.3164

Fax: 218.529.7301

Email: tengelmann@cirrusaircraft.com

Cc: Wesley Rouse, Chicago ACO