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**DEPARTMENT OF TRANSPORTATION Federal Aviation Administration**  **14 CFR Part 39 [Docket No. FAA** **- 20**  **15 -**  **0869 ; Directorate Identifier**  **2015 -** **NE -**  **11 -** **AD ]**  **RIN 2120 -** **AA64 Airworthiness Directives;**  **Pratt & Whitney Turbofan Engines AGENCY:**  Federal Aviation Administration (FAA), DOT. **ACTION:** Notice of proposed rulemaking (NPRM). **SUMMARY:** We propose to adopt a new airworthiness directive (AD) for all Pratt & Whitney (PW) PW4164, PW4168, PW4168A, PW4164 - 1D, PW4168 - 1D, PW4168A - 1D , and PW4170 turbofan engines. This p roposed AD was prompted by crack finds in the 6 th stage low -pressure turbine (LPT) disk. This proposed AD would require removal of affected 6 th stage LPT disks. We are proposing this AD to prevent failure of the 6 th stage LPT disk , which could lead to an uncontained disk release, damage to the engine, and damage to the airplane. **DATES:** We must receive comments on this proposed AD b y [ INSERT DATE 60 DAYS AFTER DATE OF PUBLICATION IN THE Federal Register]. **ADDRESSES:** You may send comments , using the procedure s found in 14 CFR 11.43 and 11.45, b y any of the following methods: • Federal eRulemaking Portal: Go to http://www.regulations.gov . Follow the instructions for submitting comments. • Fax: 202 - 493 - 2251. • Mail: U.S. Department of Transportation, Docket Operations, M - 30, West Building Ground Floor, Room W12 - 140, 1200 New Jersey Avenue SE., Washington, DC 20590 .2 • Hand Delivery : Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through Friday , except Federal holidays . For service information identified in this proposed AD, contact Pratt & Whitney , 400 Main St., East Hartford, CT 06108; phone: 860 - 565 - 8770; fax: 860 - 565 - 4503 . You may view this service information at the FAA, Engine & Propeller Directorate, 12 New England Executive Park, Burlington, MA. For information on the availability of this material at the FAA, call 781 - 238 - 7125. **Examining the AD**  **Docket** You may examine the AD docket on the Internet at http://www.regulations.gov by searching for and locating Docket No. FAA - 20 15 - 0869 ; or in perso n at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday , except Federal holiday s. The AD docket contains this proposed AD, the regulatory evaluation, any comments received , and other information. The street address for the Dock et Office (phone : 800 - 647 - 5527) is in the ADDRESSES section. C omments will be available in the AD docket shortl y after receipt. **FOR FURTHER INFORMATION CONTACT:** Kathery n Malatek, Aerospace Engineer, Engine Certification Office, FAA, Engine & Propeller Dire ctorate, 12 New England Executive Park, Burlington, MA 01803; phone: 781 - 238 - 7747; fax: 781 - 238 - 7199; email: kathery

n.malatek@faa.gov. **SUPPLEMENTARY INFORMATION: Comments Invited**  We invite you to send any written relevant data, views, or arguments about this NPRM . Send your comments to an address listed under the ADDRESSES section. In clude “Docket No. FAA - 2015 - 0869 ; Directorate Identifier 2015 -NE - 11 - AD ” at the beginning of your comments. We specificall y invite comments on the overall regulatory, economic, environmental, and energy aspects of this NPRM . We will consider all3

comments received b y the closing date and may amend this NPRM because of those comments. We will post all comments we receive, without change, to http://www.regulations.gov , including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this NPRM . **Discussion** We received reports of two crack finds in the front and rear knife - edge seals on the forward arm of the 6 th stag e LPT disk during a scheduled heavy maintenance shop visit. The suspected root cause of the cracks is residual stress introduced during knife edge weld repair. This condition, if not corrected, could result in failure of the 6 th stage LPT disk , which could lead to an uncontained disk release, damage to the engine, and damage to the airplane. **Related Service Information**  **under 1 CFR Part 51** We reviewed PW Service Bulletin No. PW4G - 100 - 7 2 - 252 , dated November 18 , 2014. This service information identifies and directs removal of the suspect 6 th stage LPT disks. This service information is reasonabl y available because the interested parties have access to it through their normal course of business or see ADDRESSES for other way s to access this service information. **FAA’s Determ ination**  We are proposing this NPRM because we evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the same ty pe design . **Proposed AD Requirements** This NPRM would require removing certain serial number 6 th stage LPT disks, part number 50N886.4

**Costs of Compliance** We estimate that this proposed AD would affect 18 engines installed on airplanes of U.S. registry . We also estimate that no additional hours would be required per engine to comply

with this proposed AD because the engine is already disassembled in the shop when we require the part to be removed. The average labor rate is $85 per hour. We estimate that 6 of the engines will require replacement part s during an LP T shop visit , and that the prorated replacement parts cost would be $ 108,800 per engine. Based on these figures, we estimate the cost of this proposed AD on U.S. operators to be $ 652,800 . **Authority for this Rulemaking** Title 49 of the United S tates Code specifies the FAA’s authority to issue rules on aviation safety. Subtitle I, section 106, describes the autho rity of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency ’s authority . We are iss uing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: “ General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identifi ed in this rulemaking action. **Regulatory Findings** We determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD 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.5 For the reasons discussed above, I certify this proposed regulation: ( 1 ) Is not a “significant regulatory action” under Ex ecutive Order 12866 , ( 2 ) Is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979), (3) Will not affect intrastate aviation in Alaska to the extent that it justifies making a regulatory

distinction, and ( 4) 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. **List of Subjects in 14 CFR Part 39** Air transportation , Aircraft, Aviation safety, In corporation by reference, Safety . **The Proposed Amendment** Accordingl y, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows: **PART 39 -**  **AIRWORTHINESS DIRECTIVES** 1. The authority citation for part 39 continue s to read as follows: Authority : 49 U.S.C. 106(g), 40113, 44701. **§ 39.13 [Amended]** 2. The FAA amends § 39.13 by adding the following new airworthiness directive (AD ) : **Pratt & Whitney** : Docket No. FAA - 2015 - 0869 ; Directorate Identifier 20 15 -NE - 11 - AD . **(a) Comm**  **ents Due Date** We must receive comments by [ INSERT DATE 60 DAYS AFTER DATE OF PUBLICATION IN THE Federal Register]. **(b) Affected ADs**  None .6

**(c) Applicability**  This AD applies to all Pratt & Whitney (PW) PW4164, PW4168, PW4168A, PW4164 - 1D, PW4168 - 1D, PW4168A - 1 D , and PW4170 turbofan engines with 6 th stage low -pressure turbine (LPT) disks , part number 50N886, installed. **( d**  **) Unsafe Condition**  This AD was prompted by crack finds in the 6 th stage LPT disk. We are issuing this AD to prevent failure of the 6 th stage LP T disk , which could lead to an uncontained disk release, damage to the engine, and damage to the airplane. **(e) Compliance**  Comply with this AD within the compliance times specified, unless already done. At the next LP T shop visit after the effective date of this AD, remove from service 6 th stage LP T disks with serial numbers listed in the Accomplishment Instructions, Table 1, of PW Service Bulletin (SB) No. PW4G - 100 - 7 2 - 252 , dated November 18 , 2014 . **( f**  **) Definition** For the purpose of this AD , an “LPT shop visi t” is defined as maintenance which involves disassembly

of the LPT rotor module. **( i** **) Alternative Methods of Compliance (AMOCs)**  The Manager, Engine Certification Office, FAA, may approve AMOCs for this AD. Use the procedures found in 14 CFR 39.19 to make yo ur request. You may email yo ur request to: ANE - AD - AMOC@faa.gov. **( j**  **) Related Information**  (1) For more information about this AD, contact Kathery n Malatek, Aerospace Engineer, Engine Certification Office, FAA, Engine & Propeller Directorate, 12 New England Executive Park, Burlington, MA 01803; phone: 781 - 238 - 7747; fax: 781 - 238 - 7199; email: kathery

n.malatek@faa.gov .7 (2) PW SB No. PW4G - 100 - 72 - 252, dated November 18, 2014 , can be obtained from Pratt & Whitney using the contact information in paragraph (j)(3) of this proposed rule. (3) For service information identified in this proposed rule , contact Pratt & Whitney, 400 Main St., East Hartford, CT 06108; phone: 860 - 565 - 8770; fax: 860 - 565 - 4503 . (4) You may

view this service information at the FAA, Engine & Propell er Directorate, 12 New England Executive Park, Burlington, MA. For information on the availability

of this material at the FAA, call 781 - 238 - 7125. Issued in Burlington, Massachusetts, on May 12 , 2015. Colleen M. D’Alessandro, Assistant Directorate Manager, Engine & Propeller Directorate, Aircraft Certification Service.