u.s. Deportment

of Transportation

Federal Aviotlon

Administration

In Reply 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

for Notice of Proposed 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.

We have reviewed the information contained in your 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 to NPRM 10-10 have been posted for public conunent. Four of

the five new or revised ACs have comment periods ending with the NPRM. The proposed

revision to AC 20-147, which was the primary concerri noted in your letter, was posted on

September 1, 2010 and has a comment period which ends on November 1, 2010. NPRM 10-10

and the related guidance is the result of recommendations made by an Aviation Rulemaking

Advisory Committee. Following completion of the recOimnendations made in 2005, a Phase IV

review was conducted by the ARAC working group dJe to the immature state oflarge drop icing

simulation and compliance methods at the time, with completion in March 2009. The

recommendations made following the Phase N review were incorporated into the only new

proposed AC, 25-xx, which has been available for public 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 Association
U.S.Department

of Transportation

Federal Aviation

Administration

SE? 1 0 1010

In Reply 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 to the comment period

for Notice of Proposed 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 in your letter but have determined to retain the

current NPRM comment period, which closes September 29, 2010. All of the revised or new

advisory circulars (ACs) related to NPRM 10-tO have been posted for public comment. Four of

the five new or revised ACs have comment periods el1ding with 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 a comment period which ends on November I, 2010. NPRM 10-10

and the related guidance is the result ofrecornmendations made by an Aviation Rulemaking

Advisory Committee. Following completion of the recommendations made in 2005, a Phase IV

review was conducted by the ARAC working group due to the immature state of large drop icing

simulation and compliance methods at the time, with Gompletion in March 2009. The

recommendations made following the Phase N revieJr were incorporated into the only new

proposed AC, 25-xx, which has been available for public comment since July 2, 2010 and

remains available for comment until September 30, 20to.

Sincerely,

..-:I. Ali Bahrami

f"O...-- Manager, Transport Airplane Directorate

Aircraft Certification Service

Cc: Mr. Todd Sigler, Aerospace Industries Association