AD 2017-18-14

This AD is effective October 13, 2017.

See the FOR FURTHER INFORMATION CONTACT section.

John Tallarovic, Aerospace Engineer, FAA, Chicago ACO Branch, Compliance and Airworthiness Division, 2300 E. Devon Ave., Des Plaines, IL 60018; phone: 847-294-8180; fax: 847-294-7834; email: john.m.tallarovic@faa.gov.

We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to supersede AD 2015-02-22, Amendment 39-18090 (80 FR 5452, February 2, 2015), (“AD 2015-02-22”). AD 2015-02-22 applied to certain RRC 250-B17, -B17B, -B17C, -B17D, -B17E, -B17F, -B17F/1, -B17F/2, turboprop engines; and 250-C20, -C20B, -C20F, -C20J, -C20R, -C20R/1, -C20R/2, -C20R/4, -C20S, and -C20W turboshaft engines. The NPRM published in the Federal Register on March 29, 2017 (82 FR 15474). The NPRM was prompted by our determination that it is necessary to remove the 4th-stage wheels at the next inspection. The NPRM proposed to require repetitive visual inspections and FPIs of 3rd-stage turbine wheels while removing from service 4th-stage turbine wheels. We are also revising the applicability to remove all RRC turboprop engines and add additional turboshaft engines. We are issuing this AD to prevent failure of the 3rd-stage and 4th-stage turbine wheel blades, damage to the engine, and damage to the aircraft.

We gave the public the opportunity to participate in developing this AD. The following presents the comments received on the NPRM and the FAA's response to each comment.

RRC requested that we remove references in this AD to the 3rd stage turbine wheel, part number (P/N) RR30000236, installed on the RRC 250-C300/A1 and 250-C300/B1 turboshaft engines. RRC indicated that 3rd stage turbine wheels, P/N RR30000236, are not susceptible to cracks. RRC noted that there have been no cracks observed on 3rd stage wheels installed on RRC 250-C300/A1 or 250-C300B/1 engines.

We agree. The 3rd stage turbine wheel, P/N RR30000236, installed on RRC 250-C300/A1 and 250-C300/B1 engines does not require inspections. They are subject to less severe operating conditions and are not susceptible to this type of failure. We removed references to the 3rd stage turbine wheel, P/N RR30000236, from this AD.

RRC requested that we change references in this AD from “power turbine” to “turbine.” RRC noted that this AD should refer to the entire turbine module rather than just to the power turbine. RRC also commented that the risk analysis for this AD is based on changing the parts anytime the turbine is being serviced, not just the power turbine. Revising the reference in this AD to “turbine” would remove the affected 4th stage turbine wheels from the fleet in a shorter time period since the actions specified in this AD are to be complied with whenever the turbine is at the shop and is dissembled for any reason, or at the next turbine wheel replacement, whichever occurs first.

We agree. We changed the reference in the Compliance section of this AD from “power turbine” to “turbine.”

RRC also commented that changing the references to “turbine” would allow for removal of the Definition section from this AD.

We disagree. The term “engine shop visit” is used as one of the criteria in this AD to determine when an inspection of affected applicable turbine wheels is required. Given that “engine shop visit” may be interpreted in different ways, we provide a definition for this term in this AD. We did not change this AD.

RRC requested that we revise the Compliance section of this AD so that it does not require removal from service all turbine wheels found with cracks. RRC commented that only certain cracks are related to this AD and are a safety concern.

We agree. The intent of this AD is to address cracks at the trailing edge of the turbine wheel blades, near the fillet at the rim. The maintenance manuals for these engines allow certain cracks in areas of the turbine wheels not subject to this AD. Engines may still operate safety with turbine wheels that have allowable cracks. We revised paragraph (f)(3) of this AD to refer to cracks found at the trailing edge, near the fillet at the rim, of the turbine blades.

We reduced the estimated cost of inspection of 3rd stage wheels from $320,365 to $288,320 since we removed the 3rd stage wheel, P/N RR30000236, from the applicability of this AD. As noted in our previous comment response, these P/N 3rd stage wheels are not subject to the unsafe condition identified in this AD.

We reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting this AD with the changes described previously and minor editorial changes. We have determined that these minor changes:

• Are consistent with the intent that was proposed in the NPRM for correcting the unsafe condition; and

• Do not add any additional burden upon the public than was already proposed in the NPRM.

We also determined that these changes will not increase the economic burden on any operator or increase the scope of this AD.

We estimate that this AD affects 3,769 engines installed on airplanes of U.S. registry.

We estimate the following costs to comply with this AD:

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority.

We are issuing 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 identified in this rulemaking action.

This AD is issued in accordance with authority delegated by the Executive Director, Aircraft Certification Service, as authorized by FAA Order 8000.51C. In accordance with that order, issuance of ADs is normally a function of the Compliance and Airworthiness Division, but during this transition period, the Executive Director has delegated the authority to issue ADs applicable to engines, propellers, and appliances to the Manager, Engine and Propeller Standards Branch, Policy and Innovation Division.

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 this AD:

(1) Is not a “significant regulatory action” under Executive Order 12866,

(2) Is not a “significant rule” under 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.

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows:

1. The authority citation for part 39 continues to read as follows:

2. The FAA amends § 39.13 by removing Airworthiness Directive (AD) 2015-02-22, Amendment 39-18090 (80 FR 5452, February 2, 2015), and adding the following new AD: