On May 4, 2004, we became aware of three reports of third-stage turbine wheel blade and shroud failures on RRC model 250-C28 series turboshaft engines. Investigation by RRC revealed that high cycle fatigue caused the third-stage turbine blade and shroud failures. Investigation has also revealed that this high cycle fatigue condition is limited to a population of 73 third-stage turbine wheels that were manufactured and inadvertently accepted with a blueprint variance. The turbine wheel original life limits were 4,550 operating hours and 6,000 cycles-in-service. This condition, if not corrected, could result in loss of power and uncommanded engine shutdown due to failure of third- stage turbine blades and shrouds.
FAA's Determination and Requirements of This AD
The unsafe condition described previously is likely to exist or develop on other RRC 250-C28 series engines of the same type design. We are issuing this AD to prevent loss of power and uncommanded engine shutdown due to failure of third-stage turbine blades and shrouds. This AD requires replacing the third-stage turbine wheels, P/N 6899383, with SNs listed in the compliance section of this proposed AD at the following:
For any turbine wheel with fewer than 250 operating hours time since new (TSN) on the effective date of the proposed AD, before accumulating 300 operating hours TSN; and
For any turbine wheel with 250 or more operating hours TSN on the effective date of the proposed AD, before accumulating an additional 50 operating hours.
FAA's Determination of the Effective Date
Since an unsafe condition exists that requires the immediate adoption of this AD, we have found that notice and opportunity for public comment before issuing this AD are impracticable, and that good cause exists for making this amendment effective in less than 30 days.
Docket Management System (DMS)
We have implemented new procedures for maintaining AD dockets electronically. As of May 17, 2004, we posted new AD actions on the DMS and assigned a DMS docket number. We track each action and assign a corresponding Directorate identifier. The DMS docket No. is in the form "Docket No. FAA-2004-18538." Each DMS docket also lists the Directorate identifier ("Old Docket Number") as a cross-reference for searching purposes.
Comments Invited
This AD is a final rule that involves requirements affecting flight safety and was not preceded by notice and an opportunity for public comment; however, we invite you to submit any written relevant data, views, or arguments regarding this AD. Send your comments to an address listed under ADDRESSES. Include "AD Docket No. FAA-2004-18538; Directorate Identifier 2004-NE-29-AD" in the subject line of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify it.
We will post all comments we receive, without change, to http://dms.dot.gov , including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this AD. Using the search function of the DMS web site, anyone can find and read the comments in any of our dockets, including the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review the DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78) or you may visit http://dms.dot.gov.
We are reviewing the writing style we currently use in regulatory documents. We are interested in your comments on whether the style of this document is clear, and your suggestions to improve the clarity of our communications with you. You can get more information about plain language at http://www.faa.gov/language and http://www.plainlanguage.gov.
Examining the AD Docket
You may examinethe docket that contains the AD, any comments received, and any final disposition in person at the DMS Docket Offices between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Office (telephone (800) 647-5227) is located on the plaza level of the Department of Transportation Nassif Building at the street address stated in ADDRESSES. Comments will be available in the AD docket shortly after the DMS receives them.
Regulatory Findings
We have determined that this AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect on the States, on the relationship between the national Government and the States, or on the distribution of power and responsibilities among the various levels of government.
For the reasons discussed above, I certify that the regulation:
1. Is not a "significant regulatory action" under Executive Order 12866;
2. Is not a "significant rule" under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and
3. Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.
We prepared a summary of the costs to comply with this AD and placed it in the AD Docket. You may get a copy of this summary at the address listed under ADDRESSES.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Safety.
Adoption of the Amendment
Under the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. The FAA amends Sec. 39.13 by adding the following new airworthiness directive: