u.s. Deportment

of Transportation Federal Aviotlon Administration

InReply Refer To: ANM-112-10-004

Todd Sigler Assistant Vice President Civil Aviation, Aerospace Industries Association 1000 Wilson Blvd, Suite 1700 Arlington, VA 22209 Transport Airplane Directorate 1601 Und Ave SW Renton, WA 98057-3356

Dear Mr. Sigler, I Thank you for your letter dated August 31, 2010, requesting an extension to the conunent period forNotice ofProposed Rulemaking (NPRM) 10-10 (Docket: FAA-2010-0636). This pertains to proposed Airplane and Engine Certification Requirements in Supercooled Large Drop, Mixed Phase, and Ice Crystal Icing Conditions.
Wehave reviewed the information contained inyour letter but have detennined to keep the current NPRM comment period, which closes September 29, 2010. All the revised or new advisory circulars (ACs) related toNPRM 10-10 have been posted forpublic conunent. Four of the five new orrevised ACs have comment periods ending with theNPRM. The proposed revision to AC 20-147, which was the primary concerri noted inyour letter, was posted on September 1,2010 and has acomment period which ends onNovember 1,2010. NPRM 10-10 and the related guidance isthe result ofrecommendations made by anAviation Rulemaking Advisory Committee. Following completion ofthe recOimnendations made in 2005, aPhase IV review was conducted by the ARAC working group dJe tothe immature state oflarge drop icing simulation and compliance methods atthe time, with completion inMarch 2009. The recommendations made following the Phase Nreview were incorporated into the only new proposed AC, 25-xx, which has been available forpublic comment since July 2, 2010 and remains available for comment until September 30, 20~O.



### "" l.. Ali Bahrami

- Manager, Transport Airplane Directorate Aircraft Certification Service
Cc: Gregory Bowles, General Aviation, Manufacturers AssociationU.S.Department

of Transportation Federal Aviation Administration 

## SE?10 1010 InReply Refer To: ANM-1l2-1O-005

Gregory J. Bowles Director, Engineering &Manufacturing General Aviation, Manufacturers Association 1400 K Street N.W., Suite 801 Washington, DC 20005

Dear Mr. Bowles: Transport Airplane Directorate 160t Lind Ave SW Renton. WA 98057-3356

Thank you for your letter dated August 31, 2010, requesting an extension tothe comment period forNotice ofProposed Rulemaking (NPRM) to-IO (Docket: FAA-20to-0636). This pertains to Airplane and Engine Certification Requirements in Su,percooled Large Drop, Mixed Phase, and Ice Crystal Icing Conditions.

We have reviewed the information contained inyour letter but have determined to retain the current NPRM comment period, which closes September 29, 2010. All ofthe revised or new advisory circulars (ACs) related toNPRM 10-tO have been posted forpublic comment. Four of the five new orrevised ACs have comment periods el1dingwith the NPRM. The proposed revision to AC 20-147, which was the primary concem noted in your letter, was posted on September I, 2010 and has acomment period which ends onNovember I, 2010. NPRM 10-10 and the related guidance isthe result ofrecornmendations made by anAviation Rulemaking Advisory Committee. Following completion ofthe recommendations made in 2005, aPhase IV review was conducted by the ARAC working group due to the immature state of large drop icing simulation and compliance methods atthe time, with Gompletion inMarch 2009. The recommendations made following the Phase NrevieJr were incorporated into the only new proposed AC, 25-xx, which has been available forpublic comment since July 2, 2010 and remains available forcomment until September 30, 20to. Sincerely,



## ..-:I. Ali Bahrami f"O...-- Manager, Transport Airplane Directorate Aircraft Certification Service
Cc: Mr. Todd Sigler, Aerospace Industries Association