DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2017-0141; Product Identifier 2016-SW-067-AD; Amendment
39-19154; AD 2018-02-01]
RIN 2120-AA64

Airworthiness Directives; The Enstrom Helicopter Corporation Helicopters

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: We are superseding Airworthiness Directive (AD) 2015-08-51 for
the Enstrom Helicopter Corporation (Enstrom) Model F-28A, 280, F-28C,
F-28C-2, F-28C-2R, 280C, F-28F, F-28F-R, 280F, 280FX, and 480
helicopters. AD 2015-08-51 required an inspection of the main rotor
spindle (spindle) and reporting the inspection results to the FAA. This
new AD was prompted by additional reports of cracked spindles and
requires establishing a life limit and a recurring inspection. The
actions of this AD are intended to prevent the unsafe condition on
these products.

DATES: This AD is effective February 21, 2018.

ADDRESSES: For service information identified in this final rule,
contact Enstrom Helicopter Corporation, 2209 22nd Street, Menominee,
MI; telephone (906) 863-1200; fax (906) 863-6821; or at
www.enstromhelicopter.com. You may view this referenced service
information at the FAA, Office of the Regional Counsel, Southwest
Region, 10101 Hillwood Pkwy., Room 6N-321, Fort Worth, TX 76177.

Examining the AD Docket

You may examine the AD docket on the internet at http://www.regulations.
gov in Docket No. FAA-2017-0141; 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 AD, the
economic evaluation, any comments received, and other information. The
address for the Docket Office (phone: 800-647-5527) is Document
Management Facility, U.S. Department of Transportation, Docket
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New
Jersey Avenue SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Manzoor Javed, Senior Aerospace
Engineer, Chicago ACO Branch, Compliance and Airworthiness Division,
FAA, 2300 East Devon Ave., Des Plaines, IL 60018; telephone (847) 294-
8112; email manzoor.javed@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR
part 39 to remove AD 2015-08-51, Amendment 39-18160 (80 FR 28172, May
18, 2015) (AD 2015-08-51) and add a new AD. AD 2015-08-51 applied to
Enstrom Model F-28A, 280, F-28C, F-28C-2, F-28C-2R, 280C, F-28F, F-28F-
R, 280F, 280FX, and 480 helicopters with a spindle part number (P/N)
28-14282-11 or 28-14282-13 installed. AD 2015-08-51 required conducting
a one-time magnetic particle inspection (MPI) of the spindle for cracks
and reporting the inspection results to the FAA. AD 2015-08-51 was
prompted by a fatal accident and reports of spindles with cracks. AD
2015-08-51 was issued as an interim action and was intended to detect a
crack in a spindle and prevent loss of a main rotor blade and
subsequent loss of control of the helicopter.
The NPRM published in the Federal Register on March 2, 2017 (82 FR
12308). The NPRM was prompted by additional reports of cracked
spindles. Based on review of in-service data and a fatigue analysis,
the FAA determined a life limit and recurring MPIs are necessary to
reduce the risk of a crack developing in a spindle. We also determined
the reporting requirement in AD 2015-08-51 is no longer necessary.
Accordingly, the NPRM proposed to require an MPI of the spindle every
500 hours time-in-service (TIS) until the spindle reaches its new life
limit of 1,500 hours TIS.
Since the NPRM was issued, the FAA's Aircraft Certification Service
has changed its organizational structure. The new structure replaces
product directorates with functional divisions. We have revised some of
the office titles and nomenclature throughout this Final rule to
reflect the new organizational changes. Additional information about
the new structure can be found in the Notice published on July 25, 2017
(82 FR 34564).

Comments

After our NPRM was published, we received comments from 50
commenters.

A. Support for the NPRM

One commenter supported the 500-hour repetitive inspection proposed
by the NPRM.

B. Comments Regarding the FAA's Justification of the Unsafe Condition

Many commenters, including Enstrom, disagreed with the FAA's
determination that an unsafe condition exists and requested the FAA
provide more information about the additional cracks that prompted this
AD.
Request: A few commenters noted the entire fleet has been inspected
in accordance with AD 2015-08-51 and no additional cracks were found.
Other commenters stated no additional cracks have been found in the
area of a spindle where a failure could cause a catastrophic accident.
A few commenters, including Enstrom, stated no additional cracking has
been reported in the same location as that of the accident spindle.
Other commenters requested the FAA provide information about the
number of additional reported cracks and whether there is any
correlation between cracks and manufacturing dates or suppliers.
Enstrom stated the cracked spindles discovered after the accident were
manufactured between 1975 to 1980 by two specific suppliers.
FAA Response: We agree to provide information about the cracks that
prompted this AD. Contrary to the public comments stating there were no
additional cracks found by the inspections required by AD 2015-08-51,
those inspection results revealed 34 cracked spindle assemblies. The
commenters are correct that the additional cracking was not in the same
location as that of the accident spindle. The location of the
additional 34 spindle cracks was at the hole for the cotter pin
securing the lamiflex bearing nut. However, we disagree that the
additional cracks were not in an area where a failure could cause a
catastrophic accident. A spindle assembly is a primary structural
element and a critical part. Flight with any known crack is prohibited
in primary structural elements including spindle assemblies. Regardless of the
location of the crack, failure of a spindle assembly could result in
loss of a main rotor blade.
We agree with Enstrom's comment that the cracked spindles
discovered after the accident were manufactured between 1975 to 1980 by
two specific suppliers. However, the accident helicopter had two
cracked and one failed spindle that were manufactured in 1984 by a
third manufacturer. The identities of the manufacturers are unknown.
The parts were marked differently with a letter designation at the end
depending on the manufacturer, but no manufacturing records exist to
indicate which letter corresponds to which manufacturer. Therefore, no
investigation could be conducted as to what manufacturing processes or
specifications used by these suppliers may have resulted in the
cracking. Accordingly, we cannot draw a conclusion as to whether the
manufacturer and date range are causal factors in the accident.
Request: One commenter questioned whether the FAA investigated the
possibility that the cracked spindle resulted from improper maintenance
action or procedures.
FAA's Response: As part of the accident investigation, the NTSB lab
inspected the three spindles from the accident aircraft for any tool
marks that might indicate an initiation point that was maintenance
related. They were unable to find such marks. Based on the number of
cracks found in the field and the fact that they were not all
maintained by the same organization, there is no data to suggest that
this resulted from improper maintenance.

C. Comments Regarding the Required Actions

Request: Thirty-eight commenters, including Enstrom, requested the
AD not require the 1,500-hour life limit because it would be burdensome
and unnecessary. Most of these commenters also stated that the
repetitive inspections specified by Enstrom would be effective in
identifying cracks and removing any cracked spindles from service. Four
commenters requested the life limit be higher than 1,500 hours, and
proposed alternative life limits of 4,000 hours, 6,750 hours, between
8,000 and 9,000 hours, and 15,000 hours.
FAA Response: We disagree. The corrective action outlined in the
Enstrom service information did not reduce the risk to an acceptable
level. Consequently, we used the crack data to conduct a risk
assessment in accordance with the FAA's Rotorcraft Risk Analysis
Handbook, Revision 3, dated September 10, 2014. The accident
investigation and inspection results from AD 2015-08-51 show cracked
spindles from 1,800 hours up to 9,300 hours (on the accident
helicopter). A Weibull analysis identified a life limit of
approximately 800 hours. But the goodness of fit was not high as the
times on these parts historically have not been tracked, so we assumed
the part time to be the time on the airframe, which may not be
accurate. We therefore applied an additional method to determine an
appropriate life limit. We used inspection results as baseline data to
conduct a fatigue analysis using standard fatigue methodology and
scatter factors found in Advisory Circular (AC) 23-13A, ``Fatigue,
Fail-Safe, and Damage Tolerance Evaluation of Metallic Structure For
Normal, Utility, Acrobatic, and Commuter Category Airplanes.'' While
this AC was written for small aircraft, its approach for establishing a
life limit is conventional and was the most computationally valid
method considered. This analysis resulted in a life limit of 1,500
hours. We also reviewed the potential for higher life limits, but these
resulted in unacceptably short inspection intervals. For example, a
retirement age of 10,000 hours with an initial inspection at 1,500
hours would require repetitive inspections every 75 hours to maintain
an acceptable level of risk. We rejected these short inspection
frequencies because of the potential for increased maintenance errors.
Additionally, we considered the life limit of 1,500 hours is similar to
those for spindles used in other rotorcraft.
Request: Twenty-three commenters, including Enstrom, disagreed with
the compliance time for the 500-hour initial inspection. To support
this disagreement, most of these commenters stated no cracks have been
reported on spindles with less than 1,800 hours TIS. The commenters
requested that the AD require the initial inspection within 1,500 hours
as specified in Enstrom's service information.
FAA Response: We disagree. While the commenters are correct that no
cracks have been reported on spindles with less than 1,800 hours TIS,
this factor is less significant than those discussed above. Standard
practice in addressing fatigue and life limits require inspection
intervals that provide two inspection opportunities to detect a crack
before a life limit is reached. Because the FAA determined a life limit
of 1,500 hours TIS is required for the spindles, it follows that at a
minimum initial and repetitive inspections every 500 hours TIS are
necessary.
Request: One commenter requested the AD require the spindle life
limit of 7,500 cycles instead of 1,500 flight hours.
FAA Response: We disagree. All data considered and analysis
conducted for this AD has been determined using flight hours. The
commenter states he used figure AC 27 MG 11-9 from AC 27-1B,
``Certification of Normal Category Rotorcraft,'' for his conversion.
The spectrum in that figure is an example and therefore we do not find
the commenter's conversion the most appropriate in this case.
Request: Two commenters disagreed with the AD because of the
service history of their helicopters and Enstrom's history in general.
FAA Response: The fact that the individual helicopters owned or
operated by some commenters have not experienced cracking does not
negate the existence of an unsafe condition. The risk analysis used to
support the requirements of this AD was based on in-service data
reported as a result of AD 2015-04-51. This data represents the actual
service state of the current Enstrom fleet, which is more accurate than
the factors mentioned by the commenters.

D. Requests To Allow Alternative Actions

Request: Many commenters, including Airwolf Aerospace (Airwolf),
requested the AD allow installing an Airwolf tension-torsion strap
assembly (TT strap) as a means of complying with or terminating the AD.
In support of this request, Airwolf stated that TT strap installation
completely removes the threaded area of the spindle, leaving nothing
left to inspect.
FAA Response: We disagree. The commenter's request is unnecessary.
The Airwolf TT strap installation modifies the helicopter and the
spindle, changing the P/N of the spindle, such that the AD would no
longer apply.
Request: One commenter requested that instead of a life limit, the
AD require a visual inspection of the cotter pin hole at each 100-hour
or annual inspection. No technical data supporting this request was
provided by the commenter.
FAA Response: We disagree. As explained above, the FAA has
determined a life limit is required to correct the unsafe condition.
Inspection programs alone are not sufficient to lower the risk to an
acceptable level.
Request: Four commenters stated they have already inspected the
spindles in accordance with AD 2015-08-51. One
commenter requested the AD allow a 300-hour grace period for spindles
that have already been inspected.
FAA Response: We disagree. Providing a grace period within which to
comply with a life limit essentially extends the life limit and would
not be appropriate.

E. Comments Regarding Costs of Compliance With This AD

Request: Many commenters stated that the cost to comply with this
AD is underestimated or inaccurate. These commenters stated the cost
should include the costs associated with loss of utility; should
reflect a replacement cost of $24,492 for three spindles; and should
increase the labor rate.
FAA's Response: We disagree. The cost analysis in AD rulemaking
actions typically includes only the costs associated with complying
with the AD, which does not include indirect costs such as down-time
and loss of revenue.
The parts costs for this AD were provided by the manufacturer. We
do not control any price differences or retail pricing.
The labor rate of $85 per hour is provided by the FAA Office of
Aviation Policy and Plans for the FAA to use when estimating the labor
costs of complying with AD requirements.
Request: Several commenters requested the FAA not issue the AD
because the extremely high cost will cause small operators to cease
operations.
FAA's Response: We disagree. Although the FAA sympathizes with
owners and the economic impact this AD may have, it does not negate the
need to correct the identified unsafe condition. The applicable
spindles in this design are critical for safe flight.

FAA's Determination

We have reviewed the relevant information and determined that an
unsafe condition exists and is likely to exist or develop on other
helicopters of these same type designs and that air safety and the
public interest require adopting the AD requirements as proposed.

Related Service Information

We reviewed Enstrom Service Directive Bulletin No. 0119, Revision
3, dated June 24, 2016, for Model F-28A, F-28C, F-28F, 280, 280C, 280F,
and 280FX helicopters with a spindle P/N 28-14282-11 or 28-14282-13. We
also reviewed Enstrom Service Directive Bulletin No. T-050, Revision 3,
dated June 24, 2016, for Model 480 helicopters, serial numbers 5001
through 5004 and 5006, and with a spindle P/N 28-14282-13, except those
aircraft modified with tension-torsion straps. Both service directive
bulletins specify sending the spindle to Enstrom for an MPI before the
spindle reaches 1,500 hours TIS, or within 5 hours TIS for those
spindles with 1,500 or more hours TIS. Thereafter, the service
directive bulletins specify returning the spindle to Enstrom for an MPI
every 500 hours.

Differences Between This AD and the Service Information

This AD requires establishing a spindle life limit of 1,500 hours
TIS. The service information does not specify a life limit.
This AD requires that the MPI be conducted by a Level II or Level
III inspector or equivalent. The service information specifies sending
the spindle to Enstrom for an MPI.
This AD requires an initial MPI before further flight for a spindle
with 500 or more hours TIS, unless an MPI has been done within the last
500 hours TIS. The service information specifies an initial MPI
compliance time of within 5 hours TIS for a spindle with 1,500 or more
hours TIS.

Costs of Compliance

We estimate that this AD affects 323 helicopters of U.S. Registry.
We estimate that operators may incur the following costs in order to
comply with this AD. Labor costs are estimated at $85 per work-hour.
Inspecting the spindles takes about 15 work-hours for an estimated cost
of $1,275 per helicopter and $411,825 for the U.S. fleet per inspection
cycle. Replacing a cracked spindle costs $8,164 for parts and no
additional work-hours. Replacing a set of three spindles that have
reached their life limit takes about 14 work-hours and parts will cost
$17,500 for a total cost of $18,690 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 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 a regulatory distinction is required; 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, Incorporation by
reference, Safety.

Adoption of the Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 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. The FAA amends Sec. 39.13 by removing Airworthiness Directive (AD)
2015-08-51, Amendment 39-18160 (80 FR 28172, May 18, 2015), and adding
the following new AD: