Airworthiness Directives; Rolls-Royce Corporation Models 250-C30, 250-C40, and 250-C47 Series Turboshaft Engines

[Federal Register Volume 71, Number 188 (Thursday, September 28, 2006)]
[Rules and Regulations]
[Pages 56864-56866]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 06-8230]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2005-23392; Directorate Identifier 2005-NE-47-AD; 
Amendment 39-14776; AD 2006-20-07]
RIN 2120-AA64


Airworthiness Directives; Rolls-Royce Corporation Models 250-C30, 
250-C40, and 250-C47 Series Turboshaft Engines

AGENCY: Federal Aviation Administration (FAA), Department of 
Transportation (DOT).

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for 
Rolls-Royce Corporation (RRC) models 250-C30, 250-40, and 250-C47 
series turboshaft engines with a third-stage turbine wheel, part number 
(P/N) 6898663 or P/N 23065843 installed, or a fourth-stage turbine 
wheel, P/N 6892764 or P/N 23066744, installed. This AD adds an 
additional life limit for third- and fourth-stage turbine wheels. This 
AD results from analysis by RRC of failures of third-stage turbine 
wheels. We are issuing this AD to prevent loss of power, possible 
engine shutdown, or uncontained engine failure.

DATES: This AD becomes effective November 2, 2006. The Director of the 
Federal Register approved the incorporation by reference of certain 
publications listed in the regulations as of November 2, 2006.

ADDRESSES: You can get the service information identified in this AD 
from Rolls-Royce Corporation, P.O. Box 420, Indianapolis, IN 46206-
0420; telephone (317) 230-6400; fax (317) 230-4243.
    You may examine the AD docket on the Internet at http://dms.dot.gov 
or in Room PL-401 on the plaza level of the Nassif Building, 400 
Seventh Street, SW., Washington, DC.

FOR FURTHER INFORMATION CONTACT: John Tallarovic, Aerospace Engineer, 
Chicago Aircraft Certification Office, FAA, 2300 East Devon Avenue, Des 
Plaines, IL 60018-4696; telephone (847) 294-8180; fax (847) 294-7834.

SUPPLEMENTARY INFORMATION: The FAA proposed to amend 14 CFR part 39 
with a proposed AD. The proposed AD applies to RRC models 250-C30, 250-
40, and 250-C47 series turboshaft engines. We published the proposed AD 
in the Federal Register on January 25, 2006 (71 FR 4065). That action 
proposed to add an additional life limit for third- and fourth-stage 
turbine wheels.

Examining the AD Docket

    You may examine the docket that contains the AD, any comments 
received, and any final disposition in person at the Docket Management 
Facility Docket Office 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.

Comments

    We provided the public the opportunity to participate in the 
development of this AD. We have considered the comments received.

Request to Correct Factual Errors

    One commenter, RRC, requests that we correct factual errors in the 
NPRM and revise the Discussion paragraph, to state that:
    <bullet> Only third-stage turbine wheels actually failed in the 
past; and
    <bullet> Only the third-stage turbine wheel (not the third-and-
fourth-stage turbine

[[Page 56865]]

wheels) could prematurely fail if operated too many times in the 
transient overspeed region.
    We agree with these factual corrections. We changed the AD by 
removing certain references to the fourth-stage turbine wheel and 
changing the AD to state that it results from analysis by RRC of 
failures of third-stage turbine wheels.

Final Rule Should Include the Lower-Speed Avoidance Range

    A private citizen states that the final rule should include the 
lower-speed avoidance range (68.4% to 87.1%) in addition to the high-
speed transient range, when counting speed excursions and retiring 
turbine wheels. The commenter gave three reasons for the request:
    First, that operation in the lower-speed avoidance range probably 
does more cumulative damage to the turbine wheel than operation in the 
high-speed excursion range. The commenter bases this on data that he 
claims shows higher stress levels at the low-speed transient range 
compared to the high-speed transient range.
    Second, the fact that the engine control unit does not record 
operation in the low-speed avoid range, emphasizes the importance to 
inform operators about the danger of cumulative damage.
    Third, the current commercial engine bulletin gives no information 
about cumulative damage in the low-speed avoid range. The commenter 
states that currently there is no warning to operators of the potential 
damage to turbine wheels operated for any length of time in the avoid 
range which may cause more cumulative damage than high-speed 
excursions.
    We do not agree. The supporting data the commenter provided 
includes information from a manufacturer development configuration that 
does not represent the current production configuration. The data also 
does not represent the manufacturer's current, more detailed, knowledge 
of the stresses on the turbine airfoils. Transients in the low-speed 
range do not need to be tracked and used to retire turbine wheels. The 
low-speed range from 22,000 rpm to 28,045 rpm is a speed range that is 
normally passed through transiently, during the start up and shutdown 
procedures. The rate of speed change during the start up or shutdown is 
high enough that no significant time is spent at any resonant speed and 
no significant dynamic stresses are encountered that would lead to 
damage. In comparison to the low-speed excursions, if an operational 
situation occurs that results in a speed excursion above the maximum 
continuous speed, the rate of change of speed goes from positive to 
negative as it accelerates up to the maximum speed before returning 
back to the continuous operating range. During this transition, speed 
may hold close to constant, or only change very slowly, for a number of 
seconds. In this case, there could be sufficient time for the dynamic 
stresses to build to their full resonant values and potentially cause 
some level of damage to a turbine wheel. This difference between a fast 
acceleration or deceleration through a resonant speed, and a potential 
slow motion or hold in a resonant speed is why counting of occurrences 
in the low speed range is unnecessary.
    Finally, the inclusion of a specific ``steady state operation 
prohibited'' speed avoid zone denotes that failure could occur if 
operation outside of the defined continuous operating range was 
performed. RRC SB No. CEB A-72-3272, CEB A-72-5048, and CEB A-72-6054 
(combined in one document), all Revision 2, dated June 27, 2006, 
clearly instruct operators to avoid the low-speed region. As stated 
above, this speed range is not of concern for normal transient 
operation of the engine. We did not change the AD.

Conclusion

    We have carefully reviewed the available data, including the 
comments received, and determined that air safety and the public 
interest require adopting the AD with the changes described previously. 
We have determined that these changes will neither increase the 
economic burden on any operator nor increase the scope of the AD.

Costs of Compliance

    We estimate that this AD will affect 1,300 engines installed on 
airplanes of U.S. registry. We also estimate that it will take about 42 
work-hours per engine to replace the third- and fourth-stage turbine 
wheels, and that the average labor rate is $65 per work-hour. Required 
parts will cost about $25,000 per engine. We estimate that only 10% of 
all turbine wheel replacements will result from operators exceeding the 
new transient overspeed event limits. Based on these figures, we 
estimate the total potential maximum cost of the AD to U.S. operators 
to be $3,604,900.

Authority for This Rulemaking

    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.

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 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); 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, Incorporation by 
reference, Safety.

Adoption of the Amendment

0
Accordingly, under the authority delegated to me by the Administrator, 
the Federal Aviation Administration amends 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

0
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]

0
2. The FAA amends Sec.  39.13 by adding the following new airworthiness 
directive:


[[Page 56866]]


2006-20-07 Rolls-Royce Corporation (formerly Allison Engine Company, 
Allison Gas Turbine Division, and Detroit Diesel Allison): Amendment 
39-14776. Docket No. FAA-2005-23392; Directorate Identifier 2005-NE-
47-AD.

Effective Date

    (a) This airworthiness directive (AD) becomes effective November 
2, 2006.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Rolls-Royce Corporation (RRC) models 250-
C30, -C30G, -C30G/2, -C30M, -C30P, -C30R, -C30R/1, -C30R/3, -C30R/
3M, -C30S, -C30U, -C40B, -C47B, and -C47M turboshaft engines, with a 
third-stage turbine wheel, part number (P/N) 6898663 or P/N 23065843 
installed, or a fourth-stage turbine wheel, P/N 6892764 or P/N 
23066744, installed. These engines are installed on, but not limited 
to, Bell 206L-3, Bell 206L-4, Bell 230, Bell 407, Bell 430, MDHI 
369F, MDHI 369FF, MDHI 600N, and Sikorsky S-76A helicopters.

Unsafe Condition

    (d) This AD results from analysis by RRC of failures of third-
stage turbine wheels. We are issuing this AD to prevent loss of 
power, possible engine shutdown, or uncontained failure.

Compliance

    (e) You are responsible for having the actions required by this 
AD performed within the compliance times specified unless the 
actions have already been done.
    (f) Within 30 days after the effective date of this AD, record 
each time the third- and fourth-stage turbine wheels enter into the 
speed range between ``Event Threshold'' and ``Maximum Overspeed 
Transient''. Use paragraph 2.A. through 2.A.(5) of the 
Accomplishment Instructions and the applicable Figures 1 through 5 
of RRC Alert Commercial Engine Bulletins (CEBs) No. CEB A-72-3272, 
No. CEB A-72-5048, and No. CEB A-72-6054 (combined in one document), 
all Revision 2, dated June 27, 2006, to determine the speed range.
    (g) Remove and retire any third-stage turbine wheel or fourth-
stage turbine wheel after the sixth time the wheel enters into the 
speed range between ``Event Threshold'' and ``Maximum Overspeed 
Transient''.

Third- and Fourth-Stage Turbine Wheel Life Limits

    (h) The retirement criteria in this AD are in addition to the 
existing third- and fourth-stage turbine wheel hour and cycle life 
limits. You must retire the wheels when you exceed any published 
life limit (transient speed excursions, hours, or cycles).

Alternative Methods of Compliance

    (i) The Manager, Chicago Aircraft Certification Office, has the 
authority to approve alternative methods of compliance for this AD 
if requested using the procedures found in 14 CFR 39.19.

Related Information

    (j) None.

Material Incorporated by Reference

    (k) You must use Rolls-Royce Corporation Alert Commercial Engine 
Bulletins No. CEB A-72-3272, No. CEB A-72-5048, and No. CEB A-72-
6054 (combined in one document), all Revision 2, dated June 27, 
2006, to perform the actions required by this AD. The Director of 
the Federal Register approved the incorporation by reference of this 
service bulletin in accordance with 5 U.S.C. 552(a) and 1 CFR part 
51. Contact Rolls-Royce Corporation, P.O. Box 420, Indianapolis, IN 
46206-0420; telephone (317) 230-6400; fax (317) 230-4243 for a copy 
of this service information. You may review copies at the FAA, New 
England Region, Office of the Regional Counsel, 12 New England 
Executive Park, Burlington, MA; or at the National Archives and 
Records Administration (NARA). For information on the availability 
of this material at NARA, call 202-741-6030, or go to: http://www.archives.gov/federal-register/cfr/ibr-locations.html.

    Issued in Burlington, Massachusetts, on September 20, 2006.
Francis A. Favara,
Manager, Engine and Propeller Directorate, Aircraft Certification 
Service.
[FR Doc. 06-8230 Filed 9-27-06; 8:45 am]
BILLING CODE 4910-13-P

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