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###### Department of Transportation

###### Federal Aviation Administration

# AGENCY:

Federal Aviation Administration, DOT.

# ACTION:

Notice of availability of proposed advisory circular and request for comments.

# SUMMARY:

This notice announces the availability of proposed Advisory Circular (AC) No. 39XX, Continued Airworthiness Assessments of Powerplant and Auxiliary Power Unit Installations on Transport Category Airplanes.

# DATES:

Comments must be received on or before July 14, 2000.

# ADDRESSES:

Send all comments on the proposed AC to the Federal Aviation Administration, Attn: Engine and Propeller Standards Staff, ANE-110, Engine and Propeller Directorate, Aircraft Certification Service, 12 New England Executive Park, Burlington, MA, 01803-5299.

# FOR FURTHER INFORMATION CONTACT:

Ann Azevedo, Engine and Propeller Standards Staff, ANE-110, at the above address, telephone (781) 238-7117, fax (781) 238-7199. A copy of the subject AC may also be obtained electronically by writing to the following Internet address: “ann.azevedo@faa.gov”. Additionally, you may obtain a copy of the AC directly from the internet at the following address: http://www.faa.gov/​avr/​air/​acs/​draftach.htm.

# SUPPLEMENTARY INFORMATION:

## Comments Invited

                    A copy of the subject AC may be obtained by contacting the person named above under                     **FOR FURTHER INFORMATION CONTACT**                    . Interested persons are invited to comment on the proposed AC, and to submit such written data, views, or arguments as they desire. Commenters must identify the subject of the AC, and submit comments in duplicate to the address specified above. All communications received on or before the closing date for comments will be considered by the Engine and Propeller Directorate, Aircraft Certification Service, before issuance of the final AC.                

## Background

This Advisory Circular (AC) describes the Continued Airworthiness Assessment Methodologies (CAAM). The Federal Aviation Administration (FAA) Engine & Propeller Directorate (E&PD) and the Transport Airplane Directorate (TAD) may use CAAM, supplemented to meet each Directorate's needs, to identify those unsafe conditions in products that deserve priority attention. The FAA may issue an Airworthiness Directive (AD) under Part 39 of Title 14 of the Code of Federal Regulations (14 CFR part 39) to prescribe corrective actions that must be taken to address an unsafe condition in a product when “the unsafe condition is likely to exist or develop in other products of the same type design.” CAAM, as described in this proposed AC, is intended to be used for products associated with the Powerplant or Auxiliary Power Unit (APU) Installations on Transport Category Airplanes.

Continued airworthiness requires that safety concerns within the existing fleet be addressed, and the knowledge gained applied for the benefit of future fleets as well. This AC provides CAAM guidance for estimating the risks associated with identified unsafe conditions; defining, prioritizing, and selecting suitable corrective actions for all identified unsafe conditions; and verifying that the corrective actions were effective. This AC is intended to present a tangible means of logically assessing and responding to the safety risks posed by unsafe conditions.

This AC does not establish any requirement that the FAA must perform a risk assessment before issuing an AD, or that the FAA must wait to issue an AD until the design approval holder performs a risk assessment, or that the FAA must accept the findings of a risk assessment performed by the design approval holder. CAAM, as described in this proposed AC, assists the FAA in making decisions concerning the priority in which unsafe conditions should be addressed. The FAA may issue an AD for a particular unsafe condition before a risk assessment is performed, or without having an assessment performed at all.

In this regard, CAAM does not define “unsafe condition” in a powerplant or APU installation. Rather, CAAM is a tool that the FAA usually will use to make the kinds of decisions described above.

It is recognized that the proposed AC represents a significant change from the specific CAAM process detailed in draft AC39.XX that was published for public comment several years ago. Therefore, it is anticipated that comments will be received on the newly-proposed AC. The FAA does not intend to issue a final document until those comments have been appropriately reviewed and resolved.

The FAA recognizes that many manufacturers use risk assessment practices to evaluate continued airworthiness. The FAA considers these current practices to be acceptable, and no reassessment will take place until all comments with the proposed are properly dispositioned.

This proposed advisory circular, published under the authority granted to the Administrator by 49 U.S.C. 106(g), 40113, 44701-44702, 44704, provides guidance for the use of CAAM.

Issued in Burlington, Massachusetts, on May 4, 2000.

David A. Downey, 

Assistant Manager, Engine and Propeller Directorate, Aircraft Certification Service.

[FR Doc. 00-12145  Filed 5-12-00; 8:45 am]

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