[Federal Register Volume 78, Number 80 (Thursday, April 25, 2013)]
[Proposed Rules]
[Pages 24363-24366]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2013-09767]


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 Proposed Rules
                                                 Federal Register
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
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  Federal Register / Vol. 78, No. 80 / Thursday, April 25, 2013 / 
Proposed Rules  

[[Page 24363]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2008-0442; Directorate Identifier 2007-SW-24-AD]
RIN 2120-AA64


Airworthiness Directives; Various Sikorsky-Manufactured Transport 
and Restricted Category Helicopters

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Supplemental notice of proposed rulemaking (SNPRM); reopening 
of comment period.

-----------------------------------------------------------------------

SUMMARY: We are revising the proposals in an earlier notice of proposed 
rulemaking (NPRM) for certain Sikorsky Aircraft Corporation (Sikorsky) 
Model S-61A, D, E, L, N, NM (serial number 61454), R, and V; Croman 
Corporation Model SH-3H, Carson Helicopters, Inc., Model S-61L; Glacier 
Helicopters, Inc. Model CH-3E; Robinson Air Crane, Inc. Model CH-3E, 
CH-3C, HH-3C, and HH-3E; and Siller Helicopters Model CH-3E and SH-3A 
helicopters. The NPRM proposed superseding an existing AD but retaining 
some requirements of that AD, removing certain dowel pin bores, 
expanding the applicability to include additional helicopters, and 
implementing a new retirement life for each main rotor shaft (MRS) 
based on a reevaluation of the MRS service life. This SNPRM is prompted 
by the comments received in response to the NPRM and a reevaluation of 
the relevant data. The proposed actions are intended to prevent MRS 
structural failure, loss of power to the main rotor, and subsequent 
loss of control of the helicopter.

DATES: We must receive comments on this SNPRM by June 24, 2013.

ADDRESSES: You may send comments by any of the following methods:
     Federal eRulemaking Docket: Go to http://www.regulations.gov. Follow the instructions for sending your comments 
electronically.
     Fax: 202-493-2251.
     Mail: Send comments to the U.S. Department of 
Transportation, Docket Operations, M-30, West Building Ground Floor, 
Room W12-140, 1200 New Jersey Avenue SE., Washington, DC 20590-0001.
     Hand Delivery: Deliver to the ``Mail'' address between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.

Examining the AD Docket

    You may examine the AD docket on the Internet at http://www.regulations.gov or in person at the Docket Management Facility 
between 9 a.m. and 5 p.m., Monday through Friday, except Federal 
holidays. The AD docket contains this proposed AD, the regulatory 
evaluation, any comments received, and other information. The street 
address for the Docket Office (phone: 800-647-5527) is in the ADDRESSES 
section. Comments will be available in the AD docket shortly after 
receipt.
    For service information identified in this AD, contact Sikorsky 
Aircraft Corporation, Attn: Manager, Commercial Technical Support, 
mailstop s581a, 6900 Main Street, Stratford, CT, telephone (203) 383-
4866, email address [email protected], or at http://www.sikorsky.com. You may review a copy of the referenced service 
information at the FAA, Office of the Regional Counsel, 2601 Meacham 
Blvd., Room 663, Fort Worth, Texas 76137.

FOR FURTHER INFORMATION CONTACT: Jeffrey Lee, Aviation Safety Engineer, 
Boston Aircraft Certification Office, 12 New England Executive Park, 
Burlington, MA 01803, telephone (781) 238-7161, fax (781) 238-7170, 
email [email protected].

SUPPLEMENTARY INFORMATION: 

Comments Invited

    We invite you to participate in this rulemaking by submitting 
written comments, data, or views. We also invite comments relating to 
the economic, environmental, energy, or federalism impacts that might 
result from adopting the proposals in this document. The most helpful 
comments reference a specific portion of the proposal, explain the 
reason for any recommended change, and include supporting data. To 
ensure the docket does not contain duplicate comments, commenters 
should send only one copy of written comments, or if comments are filed 
electronically, commenters should submit only one time.
    We will file in the docket all comments that we receive, as well as 
a report summarizing each substantive public contact with FAA personnel 
concerning this proposed rulemaking. Before acting on this proposal, we 
will consider all comments we receive on or before the closing date for 
comments. We will consider comments filed after the comment period has 
closed if it is possible to do so without incurring expense or delay. 
We may change this proposal in light of the comments we receive.

Discussion

    On April 10, 2008, we issued an NPRM (73 FR 21556, April 22, 2008) 
proposing to amend 14 CFR part 39 to include an AD for Sikorsky 
Aircraft Corporation Model S-61A, D, E, L, N, NM, R, and V; Croman 
Corporation Model SH-3H, Carson Helicopters, Inc. Model S-61L; Glacier 
Helicopters, Inc. Model CH-3E; Robinson Air Crane, Inc. Model CH-3E, 
CH-3C, HH-3C and HH-3E; and Siller Helicopters Model CH-3E and SH-3A 
helicopters. That NPRM proposed superseding AD 98-26-02, published in 
the Federal Register on December 16, 1998 (63 FR 69177), that only 
applied to the affected Sikorsky model helicopters. That NPRM proposed 
retaining some of the requirements of the existing AD but also proposed 
determining a new retirement life for each MRS, removing from service 
any MRS with oversized dowel pin bores, and expanding the applicability 
to include certain restricted category models that were inadvertently 
omitted in the current AD. That NPRM was prompted by the manufacturer's 
reevaluation of the retirement life for the MRS based on torque, 
ground-air-ground (GAG) cycle, and fatigue testing. Those proposals 
were intended to prevent MRS structural failure, loss of power to the 
main rotor, and subsequent loss of control of the helicopter.

Actions Since Previous NPRM Was Issued

    Since we issued the NPRM (73 FR 21556, April 22, 2008), we have 
determined a need to revise the proposed requirements, based on our 
review of the data and the comments

[[Page 24364]]

received. These supplemental proposals are intended to extend the hours 
time-in-service (TIS) required for identifying the MRS as a repetitive 
external lift (REL) MRS to coincide with the nondestructive inspection 
(NDI) so that only one disassembly of the shaft is required, which 
would reduce the down time required to disassemble the shaft. Also, 
this action proposes to extend the time required to replace the MRS.
    This action also proposes to modify a paragraph in the AD that 
imposes a factor of 30 for unknown flight time. This has been changed 
to a factor of 13.6. This action proposes to add the determination of 
the shaft cycle count for the purpose of establishing the life limit. 
Also, this action proposes to allow additional Revision A service 
information that can be used to modify an REL MRS for its life limit 
determination.
    We are reopening the comment period to allow the public to comment 
on these proposed changes.

Comments

    We gave the public the opportunity to comment on the previous NPRM 
(73 FR 21556, April 22, 2008). The following presents the comments 
received on the NPRM, and the FAA's response to those comments.

Request

    One commenter stated there was a difference between AD 98-26-02 and 
the NPRM in how many lifts constitute the shaft being REL. The 
commenter stated that a shaft that had 6 lifts per hour is REL under AD 
98-26-02 but would not be considered REL (more than 6 lift cycles per 
hour) under the NPRM.
    We agree. The proposed AD is changed to match AD 98-26-02. Those 
shafts that have 6 or more lifts per hour are REL shafts.
    Two commenters commented on the requirement to identify the REL 
MRS. One commenter stated that the compliance time to identify the REL 
MRS should be extended from 5 hours to 10 hours. Another commenter 
asked if the identification of REL MRS on the component history card 
would be sufficient and stated that the marking requirement of the REL 
MRS would require an extended down time and lost revenue.
    We partially agree. We still believe the physical REL MRS should be 
identified and marking the component history card alone is 
insufficient. However, to avoid unnecessary down time, we are proposing 
to mark the MRS to coincide with the NDI at 1,100 hours TIS, at which 
time, the shaft would be disassembled anyway thus avoiding 
unnecessarily disassembling the MRS just to mark it.
    One commenter stated that mentioning the identification of the TS-
281 marking in the proposed ``Note 2'' could result in a serviceable 
MRS being rejected. The commenter further states that an MRS can have 
the TS-281 marking but not have oversized dowel pin holes.
    We disagree. The proposed AD would not require all shafts marked 
with the TS-281 marking to be removed from service. Only those shafts 
that have oversized dowel pin bores would be required to be removed 
from service.
    A commenter stated that compliance time (grace period) should be 
extended for the MRS over life limit because the steel plates 
referenced in the service information may not be available. Another 
commenter, the manufacturer, further stated that cycle limits should be 
added to the grace period.
    We disagree. Providing a grace period within which to comply with a 
retirement life essentially extends the retirement life and would not 
be appropriate. Also, this AD does not mandate modifying the 
configuration using the steel plates in SB 61B35-53A, and therefore the 
availability of that part does not factor into the compliance times 
identified.
    Another commenter stated that the lack of documented failures 
supports keeping the existing life limits in place and does not support 
the additional cycle limits to the MRS due to flawed testing. The 
commenter further stated that there have been no reported cracks in the 
MRS in the 9+ years since issuing AD 98-26-02. The commenter also 
stated that the life limits were generated using a flawed test program. 
Based on an approved Rotorcraft Flight Manual, the chart shows that at 
above 20 degrees Celsius and 1000-foot pressure altitude, the 
helicopter cannot produce 103 per cent torque. The capability of the 
helicopter reaching 103 percent torque was one of the reasons the 
commenter gave that the testing was flawed. Due to that capability, the 
testing at the 96 percent torque value was indicated to be more 
realistic (the test specimen lasted for longer than 1.4 million 
cycles). The second example of flawed testing given by the commenter 
was that using the 200,000 cycle in the presentation and without using 
the mean or working curve, the factor of 30 gives an equivalent time of 
over 6,660 flight hours. This would allow several 1000-hour inspections 
based on the overhaul manual to remove any of the fretting damage. 
Therefore, the fretting damage would have been repaired, resulting in a 
significant increase in cycles to failure.
    We partially agree. During certain operations, the helicopter can 
reach 103 percent torque depending on the temperature and altitude 
adjustments. The ability of the helicopter to reach 103 percent torque 
was one of the reasons given for flawed testing. Based on logging 
surveys conducted by Sikorsky, the current usage spectrum of some 
operators exceeds those that generated the MRS life limits. However, 
there have been no new reported cracks. During the time histories of 
engine torque available during an operator logging survey, the 103 per 
cent engine torque was seen during those operations. Because the torque 
value can be reached during logging operations, it is a realistic 
torque value for determining the new life limit.
    The second example provided of flawed testing is based on 
inspecting the specimen by following the overhaul manual and repairing 
any damage. However, when performing fatigue tests for life limit 
certification of the helicopter, these tests are carried out for the 
life of the part without any stoppage for inspections or repairs. The 
allowable cycles are further reduced due to the limited number of test 
specimens to represent the manufacturing variability and other unknown 
factors. Therefore, those cycles are modified using a reduction factor 
to determine a life limit. Since the testing to determine life limits 
does not consider repairs, the testing performed was not flawed. 
Therefore, we are proposing to retain the new life limits.
    The same commenter stated that the lack of documented failures 
supports keeping the existing life limits in place and does not support 
the additional cycle limits to the MRS because the 30,000 cycle limit 
would reduce the actual flight hour time to as low as 1,000 hours 
(using imposed 30 cycles per flight hour factor). The commenter further 
stated that the significant decrease in life limit from 2,200 hours to 
1,000 hours is not justified.
    We partially agree. Providing the factor of 30 to the unknown 
flight time to determine the component lift cycle count would reduce 
the existing life limit to below those of AD 98-26-02. Therefore, we 
are modifying the requirements by imposing a factor of 13.6 for the 
lift cycle count to the unknown flight time.
    The manufacturer stated that we should require incorporating 
Customer Service Notice (CSN) 6135-10A and Alert Service Bulletin (ASB) 
61B35-53A for unmodified REL MRS and reference these instead of the 
prior revisions. The

[[Page 24365]]

commenter further stated that we should require replacing the planetary 
assembly and MRS assembly attaching hardware with the high strength 
steel hardware for unmodified REL MRS because the titanium planetary 
plates have a history of cracks in REL operations.
    We partially agree. The titanium plates continue to be airworthy so 
long as the compliance times for the unmodified REL MRS times are 
followed. Because they are still airworthy parts, incorporating CSN 
6135-10A and ASB 61B35-53A, both dated April 29, 2004, will not be 
required for unmodified REL MRS. Operators continuing to use the 
unmodified REL MRS will continue to have a lower life limit as 
identified in AD 98-26-02 for the unmodified REL MRS in comparison to 
the life of a modified REL MRS. However, the later versions of the CSN 
and ASB (Revision A) will not be incorporated because that is 
unnecessary to correct the unsafe condition. The previous versions are 
equivalent to CSN 6135-10A and ASB 61B35-53A for determining a modified 
REL MRS configuration. Therefore, for modified REL MRS, we propose 
adding CSN 6135-10A and ASB 61B35-53A to provide credit for those 
modified by following the original ASB and CSN or revision A to those 
documents.
    The manufacturer also stated that the compliance time (grace 
period) for the non-REL MRS should be reduced to 150 from 1500 hours 
TIS.
    We disagree. Sikorsky issued ASB 61B35-69, which specified 
replacing a non-REL MRS at the next main gearbox overhaul or within 6 
months. However, as these shafts have exceeded the life limit for the 
part, it should be replaced with an airworthy part. Therefore, we are 
proposing to remove the grace period.

FAA's Determination

    We are proposing this SNPRM because we evaluated all the relevant 
information and determined the unsafe condition described previously is 
likely to exist or develop in other helicopters of these same type 
designs. Certain changes described above expand the scope of the 
original NPRM. As a result, we have determined that it is necessary to 
reopen the comment period to provide additional opportunity for the 
public to comment on this SNPRM.

Proposed AD Requirements

    This proposed AD would retain some of the requirements from the 
current AD 98-26-02 (63 FR 69177, December 16, 1998): Recording the 
number of external lift cycles, determining whether the shaft is REL or 
non-REL, marking the REL shafts at the time of the NDI, and conducting 
an NDI for shafts used in REL operations and replacing it if a crack is 
found.
    The proposed AD would also require calculating a 250-hour TIS 
moving average of lift cycles to determine whether the MRS is an REL 
MRS, determine a new retirement life for each MRS based on hour TIS and 
lift cycles, remove from service any MRS with oversized dowel pin 
bores, and expand the applicability to include certain restricted 
category models that were inadvertently omitted in the existing AD. 
Also, this proposed action would extend the retirement life of modified 
REL MRS from 2,200 hours TIS to 5,000 hours TIS but also implement 
lift-cycle retirement lives. Lastly, this action proposes allowing the 
use of Revision A service information to modify the REL MRS for life 
limit determination.

Costs of Compliance

    We estimate that this proposed AD would affect 60 helicopters of 
U.S. registry. We estimate that operators may incur the following costs 
in order to comply with this proposed AD: It would take about 2.2 work 
hours to NDI an REL MRS at $85 per work hour plus a $50 consumable 
cost, for a total cost of $237 per helicopter and $14,220 for the U.S. 
fleet. It would take 2.2 work hours at $85 per work hour to replace an 
MRS, and parts would cost $44,753, for a total cost of $44,940 per 
helicopter.

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 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.
    For the reasons discussed, I certify this proposed 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);
    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.
    We prepared an economic evaluation of the estimated costs to comply 
with this proposed AD and placed it in the AD docket.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA proposes to amend 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 removing Amendment 39-10943 (63 FR 
69177, December 16, 1998), and by adding the following new 
airworthiness directive (AD):

Sikorsky Aircraft Corporation; Croman Corporation; Carson 
Helicopters, Inc.; Glacier Helicopters, Inc.; Robinson Air Crane, 
Inc.; and Siller Helicopters: Docket No. FAA-2008-0442; Directorate 
Identifier 2007-SW-24-AD.

(a) Applicability

    This AD applies to Model S-61A, D, E, L, N, NM (serial number 
(S/N) 61454), R, V, CH-3C, CH-3E, HH-3C, HH-3E, SH-3A, and SH-3H 
helicopters with main rotor shaft (MRS), part number (P/N) S6135-
20640-001, S6135-20640-002, or S6137-23040-001, installed, 
certificated in any category.

(b) Unsafe Condition

    This AD defines the unsafe condition as MRS structural failure, 
loss of power to the main rotor, and subsequent loss of control of 
the helicopter.

[[Page 24366]]

(c) Affected ADs

    This AD supersedes AD 98-26-02 (63 FR 69177, December 16, 1998), 
Amendment 39-10943, Docket No. 96-SW-29-AD.

(d) Comments Due Date

    We must receive comments by June 24, 2013.

(e) Compliance

    You are responsible for performing each action required by this 
AD within the specified compliance time unless it has already been 
accomplished prior to that time.

(f) Required Actions

    (1) Within 10 hours time-in-service (TIS):
    (i) Create a component history card or equivalent record for 
each MRS.
    (ii) If there is no record of the hours TIS on an individual 
MRS, substitute the helicopter's hours TIS.
    (iii) If the record of lift cycles on an individual MRS is 
incomplete, add the known number of lift cycles to a number 
calculated by multiplying the number of hours TIS of the individual 
MRS by the average lift cycles calculated according to the 
instructions in Section I of Appendix I of this AD or by a factor of 
13.6, whichever is higher.
    (iv) At the end of each day's operations, record the number of 
external lift cycles (lift cycles) performed and the hours TIS. An 
external lift cycle is defined as a flight cycle in which an 
external load is picked up, the helicopter is repositioned (through 
flight or hover), and the helicopter hovers and releases the load 
and departs or lands and departs.
    (2) Within 250 hours TIS, determine whether the MRS is a 
repetitive external lift (REL) or non-REL MRS.
    (i) Calculate the first moving average of lift cycles by 
following the instructions in Section I of Appendix I of this AD.
    (A) If the calculation results in 6 or more lift cycles per hour 
TIS, the MRS is an REL-MRS.
    (B) If the calculation results in less than 6 lift cycles per 
hour TIS, the MRS is a Non-REL MRS.
    (ii) If the MRS is a Non-REL MRS based on the calculation 
performed in accordance with paragraph (e)(2)(i), thereafter at 
intervals of 50 hour TIS, recalculate the average lift cycles per 
hour TIS by following the instructions in Section II of Appendix 1 
of this AD.
    (iii) Once an MRS is determined to be an REL MRS, you no longer 
need to perform the 250-hour TIS moving average calculation, but you 
must continue to count and record the lift cycles and number of 
hours TIS.
    (iv) If an MRS is determined to be an REL MRS, it remains an REL 
MRS for the rest of its service life and is subject to the 
retirement times for an REL MRS.
    (3) Within 1,100 hours TIS:
    (i) Conduct a Non-Destructive Inspection for a crack on each 
MRS. If there is a crack in an MRS, before further flight, replace 
it with an airworthy MRS.
    (ii) If an MRS is determined to be an REL MRS, identify it as an 
REL MRS by etching ``REL'' on the outside diameter of the MRS near 
the part S/N by following the Accomplishment Instructions, paragraph 
3.C., of Sikorsky Alert Service Bulletin (ASB) 61B35-69, dated April 
19, 2004.
    (4) Replace each MRS with an airworthy MRS on or before reaching 
the revised retirement life as follows:
    (i) For an REL MRS that is not modified by following Sikorsky 
Customer Service Notice (CSN) 6135-10, dated March 18, 1987, and ASB 
No. 61B35-53, dated December 2, 1981 (unmodified REL MRS), the 
retirement life is 30,000 lift cycles or 1,500 hours TIS, whichever 
occurs first.
    (ii) For an REL MRS that is modified by following Sikorsky CSN 
6135-10, dated March 18, 1987, and Sikorsky ASB No. 61B35-53 dated 
December 2, 1981, or CSN 6135-10A, Revision A, and ASB 61B35-53A, 
Revision A, both dated April 19, 2004 (modified REL MRS), the 
retirement life is 30,000 lift cycles or 5,000 hours TIS, whichever 
occurs first.
    (iii) For a non-REL MRS, the retirement life is 13,000 hours 
TIS.
    (5) Establish or revise the retirement lives of the MRS as 
indicated in paragraphs (e)(4)(i) through (e)(4)(iii) of this AD by 
recording the new or revised retirement life on the MRS component 
history card or equivalent record.
    (6) Within 50 hours TIS, remove from service any MRS with 
oversized (0.8860'' or greater diameter) dowel pin bores.

(g) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Boston Aircraft Certification Office, FAA, may 
approve AMOCs for this AD. Send your proposal to Jeffrey Lee, 
Aviation Safety Engineer, Boston Aircraft Certification Office, 12 
New England Executive Park, Burlington, MA 01803, telephone (781) 
238-7161, fax (781) 238-7170, email [email protected].
    (2) For operations conducted under 14 CFR part 119 operating 
certificate or under 14 CFR part 91, subpart K, we suggest that you 
notify your principal inspector, or lacking a principal inspector, 
the manager of the local flight standards district office or 
certificate holding district office before operating any aircraft 
complying with this AD through an AMOC.

(h) Additional Information

    (1) Sikorsky Aircraft Corporation issued an All Operators Letter 
(AOL) CCS-61-AOL-04-0005, dated May 18, 2004, with an example and 
additional information about tracking cycles and the moving average 
procedure. This AOL is not incorporated by reference but contains 
additional information about the subject of this AD.
    (2) The Overhaul and Repair Instruction (ORI) Number 6135-281, 
Part B, Step 5, and ORI 6137-041, Section III, Oversize Dowel Pin 
Bore Repair and identified on the flange as TS-281 or TS-041-3, 
which is not incorporated by reference, contains additional 
information about the subject of this AD.
    (3) For more information about the AOL or the ORI, contact 
Sikorsky Aircraft Corporation, Attn: Manager, Commercial Technical 
Support, mailstop s581a, 6900 Main Street, Stratford, CT, telephone 
(203) 383-4866, email address [email protected], or at http://www.sikorsky.com. You may review a copy of the referenced service 
information at the FAA, Office of the Regional Counsel, 2601 Meacham 
Blvd., Room 663, Fort Worth, Texas 76137.

APPENDIX I

Section I: The First Moving Average of Lift Cycles per Hour TIS

    The first moving average calculation is performed on the MRS 
assembly when the external lift component history card record 
reflects that the MRS assembly has reached its first 250 hours TIS. 
To perform the calculation, divide the total number of lift cycles 
performed during the first 250 hours TIS by 250. The result will be 
the first moving average calculation of lift cycles per hour TIS.

Section II: Subsequent Moving Average of Lift Cycles per Hour TIS

    Subsequent moving average calculations are performed on the MRS 
assembly at intervals of 50 hour TIS after the first moving average 
calculation. Subtract the total number of lift cycles performed 
during the first 50-hour TIS interval used in the previous moving 
average calculation from the total number of lift cycles performed 
on the MRS assembly during the previous 300 hours TIS. Divide this 
result by 250. The result will be the next or subsequent moving 
average calculation of lift cycles per hour TIS.

Section III: Sample Calculation for Subsequent 50 Hour TIS 
Intervals

    Assume the total number of lift cycles for the first 50 hour TIS 
interval used in the previous moving average calculation = 450 lift 
cycles and the total number of lift cycles for the previous 300 
hours TIS = 2700 lift cycles. The subsequent moving average of lift 
cycles per hour TIS = (2700-450) divided by 250 = 9 lift cycles per 
hour TIS.

(i) Subject

    Joint Aircraft Service Component (JASC) Code: 6320, Main Rotor 
Gearbox.

    Issued in Fort Worth, Texas, on April 16, 2013.
Lance T. Gant,
Acting Manager, Rotorcraft Directorate, Aircraft Certification Service.
[FR Doc. 2013-09767 Filed 4-24-13; 8:45 am]
BILLING CODE 4910-13-P