The Civil Aviation Authority (CAA), which is the airworthiness authority for the United Kingdom (UK), recently notified the FAA that an unsafe condition may exist on RR models Tay 650-15 and 651-54 turbofan engines. The CAA advises that four cracked HPC stage 11/12 spacers have been found during engine overhaul. Investigation has concluded that the spacer cracking results from prior failures of the HPC OGV retaining bolts. The separated OGV bolt material is released into a cavity between the inner seal support assembly air seal and stage 12 rotor disc assembly, damaging the disc assembly, resulting in high stresses and cracking of the HPC stage 11/12 spacer. Loose object damage resulting from OGV retaining bolt material release is clearly visible during borescope inspection of the stage 12 rotor disc assembly rear face. Based on an engineering review, a redesign has been introduced to reduce the loading on the OGV retaining bolts, introduced by mandatory service bulletin (SB) Tay-72-1498, which is terminating action for this AD.
Manufacturer's Service Information
Rolls-Royce, plc has issued mandatory SB's Tay-72-1483, Revision 2, dated October 20, 2000, Tay-72-1498, dated October 20, 2000, and Tay-72-1498, Revision 1, dated December 1, 2000, that specify procedures for:
Initial and repetitive borescope inspections, based on bolt cyclic life exposure, of the stage 12 rotor disc assembly for damage due to failed HPC OGV retaining bolts and, if necessary, replacement with serviceable parts.
Introduction of revised retaining and locking features for the HPC OGV and outer seal spacer, to eliminate stage 12 rotor disc assembly damage and stage 11/12 spacer cracking.
The CAA has classified SB's Tay-72-1483, Revision 2, dated October 20, 2000; and Tay-72-1498, Revision 1, dated December 1, 2000; as mandatory and issued AD 005-12-99, dated December 2, 1999; and AD 003-10-2000, dated December 1, 2000, in order to assure the airworthiness of these RR Tay engines in the UK.
Bilateral Airworthiness Agreement
These engines are manufactured in the UK, and are type certificated for operation in the United States under the provisions of Sec. 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the CAA has kept the FAA informed of the situation described above. The FAA has examined the findings of the CAA, reviewed all available information, and determined that AD action is necessary for products of this type design that are certificated for operation in the United States.
FAA's Determination of an Unsafe Condition and Required Actions
Since an unsafe condition has been identified that is likely to exist or develop on other RR models Tay 650-15 and 651-54 turbofan engines of the same type design, this AD is being issued to prevent an uncontained failure of the HPC stage 11/12 disc spacer, which could result in damage to the airplane. This AD requires:
Initial and repetitive borescope inspections of the stage 12 rotor disc assembly for damage due to failed HPC OGV retaining bolts, and replacement with serviceable parts as required.
Introduction of revised retaining and locking features for the HPC OGV and outer seal spacer, to eliminate stage 12 rotor disc assembly damage and stage 11/12 spacer cracking due to failed HPC OGV retaining bolts.
The actions must be done in accordance with the service bulletins described previously.
Immediate Adoption of This AD
Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days. Therefore, a situation exists that allows the immediate adoption of this regulation.
Comments Invited
Although this action is in theform of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications should identify the Rules Docket number and be submitted in triplicate to the address specified under the caption ADDRESSES. All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.
Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All commentssubmitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.
Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this action must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 2001-NE-02-AD." The postcard will be date stamped and returned to the commenter.
Regulatory Analysis
This final rule does not have federalism implications, as defined in Executive Order 13132, because it would 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. Accordingly, the FAA has not consulted with state authorities prior to publication of this final rule.
The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption ADDRESSES.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, pursuant to 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. Section 39.13 is amended by adding the following new airworthiness directive: