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###### Department of Transportation

###### Federal Aviation Administration 

# AGENCY:

Federal Aviation Administration, DOT. 

# ACTION:

Notice of Availability of Proposed Advisory Circular (AC) 25.21-1X and request for comments. 

# SUMMARY:

This notice announces the availability of and requests comments on a proposed advisory circular (AC) that provides methods acceptable to the Administrator related to the proposed certification requirements for performance and handling characteristics of transport category airplanes affected by flight in the icing conditions defined in appendix C of Title 14, Code of Federal Regulations (CFR) part 25. This notice is necessary to give all interested persons an opportunity to present their views on the proposed AC. 

# DATES:

Comments must be received on or before January 3, 2006. 

# ADDRESSES:

                            Send all comments on the proposed AC to: Federal Aviation Administration, Attention: Don Stimson, Airplane and Flight Crew Interface Branch, ANM-111, Transport Airplane Directorate, Aircraft Certification Service, 1601 Lind Avenue, SW., Renton, WA 98055-4056. Comments may also be submitted electronically to the following address:                             *don.stimson@faa.gov.*                             Comments may be inspected at the above address between 7:30 a.m. and 4 p.m. weekdays, except Federal holidays.                         

# FOR FURTHER INFORMATION CONTACT:

                            Don Stimson at the above address, telephone (425) 227-2143; facsimile (425) 227-1320, or e-mail at:                             *don.stimson@faa.gov.*

# SUPPLEMENTARY INFORMATION:

## Comments Invited 

                        Interested persons are invited to comment on the proposed AC by submitting such written data, views, or arguments, as they may desire. Commenters should identify AC 25.21-1X, and submit comments, in duplicate, to the address specified above. The Transport Standards Staff will consider all communications received on or before the closing date for comments before issuing the final AC. The AC can be found and downloaded from the Internet at:                         *www.airweb.faa.gov/​rgl*                         under “Draft Advisory Circulars.” A paper copy of the proposed AC may be obtained by contacting the person named above under the caption                         **FOR FURTHER INFORMATION CONTACT.**

## Harmonization of Standards and Guidance 

The proposed AC is based on recommendations submitted to the FAA by the Aviation Rulemaking Advisory Committee (ARAC). The FAA tasked ARAC (63 FR 50954, September 23, 1998) to provide advice and recommendations on “harmonizing” certain sections of part 25 (including section 25.21) with the counterpart standards contained in Joint Aviation Requirements (JAR) 25. The goal of “harmonization tasks,” such as this, is to ensure that: 

1. Where possible, standards and guidance do not require domestic and foreign parties to manufacture or operate to different standards for each country involved; and 

2. The standards and guidance adopted are mutually acceptable to the FAA and the foreign aviation authorities; 

3. the guidance contained in the proposed AC has been harmonized with that of the JAA, and provides a method of compliance that has been found acceptable to both the FAA and JAA. 

## Discussion 

This proposed AC sets forth acceptable methods of compliance with the provisions of 14 CFR 25.21 dealing with the certification requirements for performance and handling characteristics of transport category airplanes affected by flight in icing conditions defined in appendix C. 

                        It is one means, but not the only means, of complying with the revisions proposed in Notice No. 05-10 entitled “Airplane Performance and Handling Qualities in Icing Conditions,” published in this same edition of the                         **Federal Register**                        . Issuance of AC 25-21-1 is contingent of final adoption of the proposed revisions to part 25. Other methods of compliance with the requirements may be acceptable.                     

                        In addition, a separate Notice of Availability of Proposed Revisions to AC 25-7A, “Flight Test Guide for Certification of Transport Category Airplanes,” will be published in the                         **Federal Register**                         when issued. In that proposed AC, the FAA proposes removing the icing-related guidance from AC 25—7A because that material is addressed by the NPRM Notice No. 05-10, “Airplane Performance and Handling Qualities In Icing Conditions” and proposed AC 25.21-1, “Performance And Handling Characteristics In The Icing Conditions Specified In Part 25, Appendix C.”                     

Issued in Washington, DC, on October 27, 2005. 

John Hickey, 

Director, Aircraft Certification Service. 

[FR Doc. 05-21791 Filed 11-3-05; 8:45 am] 

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