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2018-22-03 BOMBARDIER, INC.: Amendment 39-19476; Docket No. FAA-2018-0160; Product Identifier 2017-NM-139-AD.
(a) EFFECTIVE DATE

    This AD is effective November 28, 2018.

(b) AFFECTED ADS

    This  AD  replaces  AD  2016-24-03,  Amendment 39-18720  (81 FR 88623,
    December 8, 2016) ("AD 2016-24-03").

(c) APPLICABILITY

    This AD  applies  to  Bombardier, Inc., Model DHC-8-400, -401 and -402
    airplanes, certificated in any category,  serial numbers 4001 and sub-
    sequent.

(d) SUBJECT

    Air Transport Association (ATA) of America Code 55, Stabilizers.

(e) REASON

    This AD was  prompted by reports  of cracked and  corroded barrel nuts
    found  at  the  mid-spar  location  of  the   horizontal-stabilizer-to
    -vertical-stabilizer attachment joint, and the issuance of new service
    information that includes a terminal modification. We are issuing this
    AD to address cracked and corroded barrel nuts, which could compromise
    the structural integrity of the vertical-stabilizer attachment  joints
    and lead to loss of control of the airplane.

(f) COMPLIANCE

    Comply  with this  AD within  the compliance  times specified,  unless
    already done.

(g) RETAINED DETAILED  INSPECTION OF BARREL NUTS FOR CRACKS AND CORROSION,
    WITH NO CHANGES

    This paragraph restates  the requirements of paragraphs (g)(1) and (g)
    (2) of AD 2016-24-03, with no changes.

(1) For airplanes that have accumulated 5,400 flight hours or more or have
    been in service 32  months or more since  the date of issuance  of the
    original certificate of airworthiness or  the date of issuance of  the
    original export certificate of  airworthiness, as of January  12, 2017
    (the effective date  of AD 2016-24-03):  Within 600 flight  hours or 4
    months, whichever occurs first after  January 12, 2017, do a  detailed
    visual inspection for signs of cracks and corrosion of the barrel  nut
    and cradle,  in accordance  with paragraph  3.B., "Procedure,"  of the
    Accomplishment Instructions of  Bombardier Alert Service  Bulletin A84
    -55-04, Revision C, dated May 3, 2016.

(2) For airplanes that have less than 5,400 flight hours and have been in-
    service for  less than  32 months  since the  date of  issuance of the
    original certificate of airworthiness or  the date of issuance of  the
    original export certificate of airworthiness, as of January 12,  2017:
    Before the accumulation of 6,000 total flight hours or 36 months since
    the date of issuance of  the original certificate of airworthiness  or
    the  date  of   issuance  of  the   original  export  certificate   of
    airworthiness, whichever occurs first, do a detailed visual inspection
    of the barrel nut for signs of cracks and corrosion of the barrel  nut
    and cradle,  in accordance  with paragraph  3.B., "Procedure,"  of the
    Accomplishment Instructions of  Bombardier Alert Service  Bulletin A84
    -55-04, Revision C, dated May 3, 2016.

(h) RETAINED CORRECTIVE ACTIONS, DETAILED INSPECTION,  AND  REPETITIVE IN-
    SPECTIONS,  WITH  NEW SERVICE INFORMATION,  REFERENCE  TO  TERMINATING
    ACTION, AND REFERENCE TO CORRECTIVE ACTIONS

    This paragraph restates  the requirements of paragraph (h) of AD 2016-
    24-03, with new service information and terminating action.  Depending
    on the findings of any  inspection required by paragraphs (g)  and (j)
    of this AD,  do the applicable  actions in paragraphs  (h)(1), (h)(2),
    (h)(3), and (h)(4) of this AD. Accomplishment of the actions  required
    by paragraphs (l)  and (m) of  this AD, as  applicable, terminates the
    requirements of this paragraph.

(1) If any barrel nut or cradle is found cracked or broken, before further
    flight, replace the barrel nut and associated hardware,  in accordance
    with paragraph 3.B.,  "Procedure,"  of the Accomplishment Instructions
    of Bombardier Service Bulletin 84-55-08,  Revision A,  dated August 2,
    2017.

(i) Concurrently with the replacement of any barrel nut, do a detailed in-
    spection  for corrosion  and damage  of the  bore of  the fitting,  in
    accordance  with paragraph  3.B., "Procedure,"  of the  Accomplishment
    Instructions  of  Bombardier Service  Bulletin  84-55-08,  Revision A,
    dated August 2, 2017, and, before further flight, repair all corrosion
    and damage, in accordance  with Bombardier Repair Drawing  (RD) 8/4-55
    -1143, Issue  1,  dated  May 21, 2015; or  Bombardier RD  8/4-55-1143,
    Issue 2,  dated May  25, 2015.  If the  bore of  the fitting cannot be
    repaired in accordance with Bombardier RD 8/4-55-1143, Issue 1,  dated
    May 21,  2015; or  Bombardier RD  8/4-55-1143, Issue  2, dated May 25,
    2015; accomplish corrective actions in accordance with the  procedures
    specified in paragraph (q)(2) of this AD. As of the effective date  of
    this AD, use Bombardier RD  8/4-55-1143, Issue 2,  dated May 25, 2015,
    for the repair required by this paragraph.

(ii) Within 600 flight hours or 4 months,  whichever  occurs  first, after
     the replacement of a cracked barrel nut, replace the remaining barrel
     nuts and  their associated  hardware at  the horizontal-stabilizer-to
     -vertical-stabilizer attachment joints, in accordance with  paragraph
     3.B., "Procedure,"  of  the Accomplishment Instructions of Bombardier
     Service Bulletin 84-55-08, Revision A, dated August 2, 2017.

(2) If any corrosion is found on any barrel nut on the front  or rear-spar
    joints, before further  flight, replace the  barrel nut in  accordance
    with paragraph 3.B.,  "Procedure," of the  Accomplishment Instructions
    of Bombardier Service Bulletin  84-55-08, Revision A, dated  August 2,
    2017,  or  accomplish  corrective  actions  in  accordance  with   the
    procedures specified in paragraph (q)(2) of this AD.

(3) If any corrosion above level 1, as defined in Bombardier Alert Service
    Bulletin  A84-55-04,  Revision C,  dated  May 3, 2016, is  found on  a
    barrel nut at the mid-spar  joint, before further flight, replace  the
    barrel nut and  accomplish corrective actions  in accordance with  the
    procedures specified in paragraph (q)(2) of this AD.

(4) If all corrosion found is at level 1 or below as defined in Bombardier
    Alert Service Bulletin A84-55-04, Revision C, dated May 3, 2016, on  a
    barrel nut at the mid-spar  joint, repeat the inspection specified  in
    paragraph (g) of this AD at  intervals not to exceed 600 flight  hours
    or 4 months, whichever occurs  first, until completion of the  actions
    required by paragraph (k) of this AD.

(i) RETAINED PRELOAD INDICATING (PLI) WASHER CHECK,  WITH  NEW TERMINATING
    ACTION

    This paragraph restates the requirements of paragraph (i) of  AD 2016-
    24-03, with  new terminating  action. For  airplanes with  PLI washers
    installed at  the front  and rear-spar  joints, before  further flight
    after accomplishing any inspection  required by paragraph (g)  of this
    AD and all applicable corrective actions required by paragraph (h)  of
    this AD,  check the  bolt preload,  and do  all applicable  corrective
    actions,  in  accordance  with  paragraph  3.B.,  "Procedure,"  of the
    Accomplishment Instructions of  Bombardier Alert Service  Bulletin A84
    -55-04, Revision C,  dated May 3, 2016.  Do all  applicable corrective
    actions before further flight. Accomplishment of the actions  required
    by paragraphs (l)  and (m) of  this AD, as  applicable, terminates the
    requirements of this paragraph.

(j) RETAINED REPETITIVE INSPECTION INTERVAL, WITH NEW TERMINATING ACTION

    This paragraph restates the requirements  of paragraph (j) of AD  2016
    -24-03, with new terminating action. Repeat the inspection and preload
    check required by paragraphs (g) and  (i) of this AD at intervals  not
    to exceed  3,600 flight  hours or  18 months,  whichever occurs first,
    except as provided by paragraph (k) of this AD. Accomplishment of  the
    actions required by paragraphs (l) and (m) of this AD, as  applicable,
    terminates the requirements of this paragraph.

(k) RETAINED OPTIONAL BARREL NUT REPLACEMENT, WITH NEW SERVICE INFORMATION

    This paragraph restates the provisions of paragraph (k) of AD 2016-24-
    03, with new  service information. Inspection  and replacement of  all
    barrel   nuts   at   the  horizontal-stabilizer-to-vertical-stabilizer
    attachment joints, in accordance with paragraph 3.B., "Procedure,"  of
    the Accomplishment Instructions  of Bombardier Service  Bulletin 84-55
    -08, Revision  A, dated  August 2,  2017, extends  the next inspection
    required by paragraph (j) of this  AD to within 6,000 flight hours  or
    36   months,   whichever  occurs   first,   after  accomplishing   the
    replacement.

(l) NEW REQUIREMENT OF THIS AD: SEALING DISK INSTALLATION

    Within 8,000 flight hours or 48 months, whichever occurs first,  after
    the effective date of this AD, install a sealing disk at the  mid-spar
    location of the vertical stabilizer in accordance with paragraph 3.B.,
    "Procedure," of the Accomplishment Instructions of Bombardier  Service
    Bulletin  84-55-06,  dated  January 31, 2017.  Accomplishment  of  the
    actions required by paragraphs (l) and (m) of this AD, as  applicable,
    terminates the requirements  of paragraphs (h),  (i), and (j)  of this
    AD.

(m) NEW REQUIREMENT OF THIS AD: REPLACEMENT OF DSC228 SERIES BARREL NUTS

    For Bombardier, Inc., Model DHC-8-400, -401 and -402 airplanes, serial
    numbers 4001 through 4524 inclusive:  Within 8,000 flight hours or  48
    months, whichever occurs first, after  the effective date of this  AD,
    replace all DSC228 series barrel nuts at the  horizontal-stabilizer-to
    -vertical-stabilizer  attachment  joints with  B0203073  series barrel
    nuts  in   accordance  with   paragraph  3.B.,   "Procedure,"  of  the
    Accomplishment Instructions of  Bombardier Service Bulletin  84-55-08,
    Revision  A,  dated  August 2, 2017.  Accomplishment  of  the  actions
    required  by  paragraphs  (l)  and  (m)  of  this  AD,  as applicable,
    terminates the requirements  of paragraphs (h),  (i), and (j)  of this
    AD.

(n) PARTS INSTALLATION PROHIBITION

    After modification of  an airplane as  required by paragraphs  (l) and
    (m) of this AD,  no person may install  a DSC228 series barrel  nut at
    the horizontal-stabilizer-to-vertical-stabilizer  attachment joint  on
    the modified airplane.

(o) TERMINATING ACTIONS FOR PARAGRAPHS (H), (I), AND (J) OF THIS AD

    Accomplishment of the  actions required by  paragraphs (l) and  (m) of
    this AD, as applicable, terminates the requirements of paragraphs (h),
    (i), and (j) of this AD.

(p) CREDIT FOR PREVIOUS ACTIONS

(1) This paragraph provides credit for actions required  by paragraphs (g)
    (1),  (g)(2),  (h)(1),  (h)(1)(i), (h)(1)(ii), (h)(2), (h)(3), (h)(4),
    (i), and (k) of this AD,  if  those actions  were performed before the
    effective date of this AD using the service information  identified in
    paragraphs (p)(1)(i) through (p)(1)(iii) of this AD.

(i) Bombardier Alert Service Bulletin A84-55-04, dated May 21, 2015, which
    is not incorporated by reference in this AD.

(ii) Bombardier Alert Service Bulletin A84-55-04, Revision A dated June 2,
     2015, which is not incorporated by reference in this AD.

(iii) Bombardier Alert Service Bulletin A84-55-04, Revision B,  dated July
      30, 2015, which is not incorporated by reference in this AD.

(2) This paragraph provides credit for actions required  by paragraphs (h)
    (1),  (h)(1)(i),  (h)(1)(ii),  (h)(2),  and (k) of this AD,  if  those
    actions were performed before the effective date of this AD  using the
    service information  identified in paragraphs (p)(2)(i) and (p)(2)(ii)
    of this AD.

(i) Bombardier Service Bulletin 84-55-08, dated January 27, 2017, which is
    not incorporated by reference in this AD.

(ii) Bombardier Alert Service Bulletin A84-55-04, Revision C, dated May 3,
     2016, which was incorporated by reference in AD 2016-24-03.

(q) OTHER FAA AD PROVISIONS

(1) Alternative Methods of Compliance (AMOCs):  The Manager,  New York ACO
    Branch,  FAA,  has  the authority  to approve  AMOCs for  this AD,  if
    requested using the  procedures found in  14 CFR 39.19.  In accordance
    with 14 CFR  39.19, send your  request to your  principal inspector or
    local Flight  Standards District  Office, as  appropriate. If  sending
    information directly to the manager of the certification office,  send
    it to ATTN: Program  Manager, Continuing Operational Safety,  FAA, New
    York ACO Branch, 1600 Stewart  Avenue, Suite 410, Westbury, NY  11590;
    telephone 516-228-7300; fax 516-794-5531.

(i) Before using any approved AMOC,  notify your appropriate principal in-
    spector, or lacking  a principal inspector,  the manager of  the local
    flight standards district office/certificate holding district office.

(ii) AMOCs approved previously for AD 2016-24-03 are approved as AMOCs for
     the corresponding provisions of this AD.

(2) Contacting the Manufacturer:  For any requirement in this AD to obtain
    corrective  actions   from  a   manufacturer,  the   action  must   be
    accomplished using  a method  approved by  the Manager,  New York  ACO
    Branch, FAA; or Transport Canada Civil Aviation (TCCA); or Bombardier,
    Inc.'s TCCA  Design Approval  Organization (DAO).  If approved  by the
    DAO, the approval must include the DAO-authorized signature.

(r) RELATED INFORMATION

(1) Refer   to   Mandatory  Continuing  Airworthiness  Information  (MCAI)
    Canadian  AD   CF-2015-13R1,  dated   June  26,   2017,  for   related
    information. This MCAI may be found  in the AD docket on the  internet
    at http://www.regulations.gov by searching for and locating Docket No.
    FAA-2018-0160.

(2) For  more information  about this AD,  contact  Aziz Ahmed,  Aerospace
    Engineer, Airframe and Propulsion Section,  FAA,  New York ACO Branch,
    1600 Stewart Avenue, Suite 410, Westbury, NY 11590; telephone 516-228-
    7329; fax 516-794-5531; email 9-avs-nyaco-cos@faa.gov.

(3) Service information  identified in this AD that is not incorporated by
    reference is available at the addresses specified in paragraphs (s)(5)
    and (s)(6) of this AD.

(s) MATERIAL INCORPORATED BY REFERENCE

(1) The Director of the Federal Register  approved  the  incorporation  by
    reference (IBR) of  the service information  listed in this  paragraph
    under 5 U.S.C. 552(a) and 1 CFR part 51.

(2) You must use  this service information as applicable to do the actions
    required by this AD, unless this AD specifies otherwise.

(3) The following service information was approved for IBR on November 28,
    2018.

(i) Bombardier Repair Drawing  (RD) 8/4-55-1143,  Issue 2,  dated  May 25,
    2015.

(ii) Bombardier Service Bulletin 84-55-06, dated January 31, 2017.

(iii) Bombardier Service Bulletin 84-55-08,  Revision A,  dated  August 2,
      2017.

(4) The following service information was approved for IBR  on January 12,
    2017 (81 FR 88623, December 8, 2016).

(i) Bombardier Alert Service Bulletin A84-55-04,  Revision C, dated May 3,
    2016.

(ii) Reserved.

(5) For  service information identified  in this AD,  contact  Bombardier,
    Inc.,  Q-Series Technical Help Desk,  123 Garratt Boulevard,  Toronto,
    Ontario M3K 1Y5, Canada;  telephone 416-375-4000; fax 416-375-4539; e-
    mail thd.qseries@aero.bombardier.com;  internet http://www.bombardier.
    com.

(6) You may view this service information at the FAA,  Transport Standards
    Branch,  2200 South 216th St., Des Moines, WA.  For information on the
    availability of this material at the FAA, call 206-231-3195.

(7) You  may  view  this  service  information  that  is  incorporated  by
    reference 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 Des Moines, Washington,  on October 12, 2018.  Michael Kaszycki,
Acting  Director,  System   Oversight  Division,  Aircraft   Certification
Service.

FOR FURTHER INFORMATION CONTACT: Aziz Ahmed, Aerospace Engineer,  Airframe
and Propulsion Section,  FAA,  New York  ACO Branch,  1600 Stewart Avenue,
Suite 410, Westbury, NY 11590;  telephone 516-228-7329;  fax 516-794-5531;
email 9-avs-nyaco-cos@faa.gov.
PREAMBLE 

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2018-0160; Product Identifier 2017-NM-139-AD; Amendment
39-19476; AD 2018-22-03]
RIN 2120-AA64

Airworthiness Directives; Bombardier, Inc., Airplanes

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

ACTION: Final rule.

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

SUMMARY: We are superseding Airworthiness Directive (AD) 2016-24-03,
which applied to certain Bombardier, Inc., Model DHC-8-400 series
airplanes. AD 2016-24-03 required repetitive detailed inspections of
barrel nuts and cradles, a check of the bolt torque of the preload
indicating (PLI) washers, and corrective actions if necessary. This AD
retains the requirements of AD 2016-24-03 and requires modifying the
airplane by installing a sealing disk to a certain location and
replacing certain barrel nuts. This AD was prompted by reports of
cracked and corroded barrel nuts found at the mid-spar location of the
horizontal-stabilizer-to-vertical-stabilizer attachment joint, and the
issuance of new service information that includes a terminal
modification. We are issuing this AD to address the unsafe condition on
these products.

DATES: This AD is effective November 28, 2018.
The Director of the Federal Register approved the incorporation by
reference of certain publications listed in this AD as of November 28,
2018.
The Director of the Federal Register approved the incorporation by
reference of certain other publications listed in this AD as of January
12, 2017 (81 FR 88623, December 8, 2016).

ADDRESSES: For service information identified in this final rule,
contact Bombardier, Inc., Q-Series Technical Help Desk, 123 Garratt
Boulevard, Toronto, Ontario M3K 1Y5, Canada; telephone 416-375-4000;
fax 416-375-4539; email thd.qseries@aero.bombardier.com; internet
http://www.bombardier.com. You may view this referenced service
information at the FAA, Transport Standards Branch, 2200 South 216th
St., Des Moines, WA. For information on the availability of this
material at the FAA, call 206-231-3195. It is also available on the
internet at http://www.regulations.gov by searching for and locating
Docket No. FAA-2018-0160.

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-2018-
0160; or in person at Docket Operations between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays. The AD docket contains
this final rule, the regulatory evaluation, any comments received, and
other information. The address for Docket Operations (phone: 800-647-
5527) is 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: Aziz Ahmed, Aerospace Engineer,
Airframe and Propulsion Section, FAA, New York ACO Branch, 1600 Stewart
Avenue, Suite 410, Westbury, NY 11590; telephone 516-228-7329; fax 516-
794-5531; email 9-avs-nyaco-cos@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR
part 39 to supersede AD 2016-24-03, Amendment 39-18720 (81 FR 88623,
December 8, 2016) (``AD 2016-24-03''). AD 2016-24-03 applied to certain
Bombardier, Inc., Model DHC-8-400 series airplanes. The NPRM published
in the Federal Register on March 9, 2018 (83 FR 10408). The NPRM was
prompted by reports of cracked and corroded barrel nuts found at the
mid-spar location of the horizontal-stabilizer-to-vertical-stabilizer
attachment joint, and the issuance of new service information that
includes a terminal modification. The NPRM proposed to continue to
require repetitive detailed inspections of each barrel nut and cradle,
a check of the bolt torque of the PLI washers, and corrective action if
necessary. The NPRM also proposed to require modifying the airplane by
installing a sealing disk to a certain location and replacing certain
barrel nuts. We are issuing this AD to address cracked and corroded
barrel nuts, which could compromise the structural integrity of the
vertical-stabilizer attachment joints and lead to loss of control of
the airplane.
Transport Canada Civil Aviation (TCCA), which is the aviation
authority for Canada, has issued Canadian AD CF-2015-13R1, dated June
26, 2017 (referred to after this as the Mandatory Continuing
Airworthiness Information, or ``the MCAI''), to correct an unsafe
condition for certain Bombardier, Inc., Model DHC-8-400 series
airplanes. The MCAI states:

There has been one in-service report of a cracked and corroded
barrel nut, part number (P/N) DSC228-12, found at the mid-spar
location of the horizontal stabilizer to vertical stabilizer
attachment joint. There have also been two other reports of corroded
barrel nuts found at mid-spar locations.
Preliminary investigation determined that the cracking is
initiated by corrosion. Further investigation confirmed that the
corrosion was caused by inadequate cadmium plating on the barrel
nuts. Failure of the barrel nuts could compromise the structural
integrity of the joint and could lead to loss of control of the
aeroplane.
The original version of this [Canadian] AD was issued to mandate
the initial and repetitive inspections of the barrel nuts [and
cradles for cracks and corrosion] at each of the horizontal
stabilizer to vertical stabilizer attachment joints.
Revision 1 of this [Canadian] AD is issued to terminate the
repetitive inspection requirement by requiring the incorporation of
a modification to install a sealing disc at the middle spar location
of the horizontal stabilizer to vertical stabilizer attachment
joint, and the replacement of the DSC228 series barrel nuts with
B0203073 series barrel nuts that are more resistant to corrosion.
The applicability has been changed to account for the introduction
of the modifications in production.

You may examine the MCAI in the AD docket on the internet at http://
www.regulations.gov by searching for and locating Docket No. FAA-2018-
0160.

Comments

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

Request To Refer to New Repair Drawing (RD)

Horizon Air requested that we revise paragraph (h)(1)(i) of the
proposed AD to refer to Bombardier RD 8/4-55-1143, Issue 2, dated May
25, 2015 (we referred to Bombardier RD 8/4-55-1143, Issue 1, dated May
21, 2015, as the appropriate source of service information for the
repair specified in paragraph (h)(1)(i) of the proposed AD). Horizon
Air noted that Bombardier RD 8/4-55-1143, Issue 2, dated May 25, 2015,
adds nominal bore diameters to sheets 1-4.
We agree with the commenter's request. Bombardier RD 8/4-55-1143,
Issue 2, dated May 25, 2015, clarifies the bore hole diameters for
repair but does not otherwise change the substantive requirements of
this AD. No additional work is necessary for airplanes on which
Bombardier RD 8/4-55-1143, Issue 1, dated May 21, 2015, has already
been done. We have revised paragraph (h)(1)(i) of this AD to include
Bombardier RD 8/4-55-1143, Issue 2, dated May 25, 2015, as the
appropriate service information for repairing corrosion and damage of
the bore of the fitting.

Conclusion

We reviewed the relevant data, considered the comment received, and
determined that air safety and the public interest require adopting
this final rule with the change 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 addressing 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 final
rule.

Related Service Information Under 1 CFR Part 51

Bombardier has issued the following service information.
Bombardier Alert Service Bulletin A84-55-04, Revision C,
dated May 3, 2016. This service information describes procedures for a
detailed inspection and repair for cracks and corrosion of the barrel
nuts and cradles; a bolt preload check of the PLI washers and
applicable corrective actions; a detailed inspection and repair for
corrosion and damage of the bore of the fitting; and replacement of the
barrel nuts.
Bombardier Service Bulletin 84-55-06, dated January 31,
2017. This service information describes procedures for installing an
aluminum sealing disk at the mid-spar location of the vertical
stabilizer.
Bombardier Service Bulletin 84-55-08, Revision A, dated
August 2, 2017. This service information describes procedures for an
inspection for part number and damage of the barrel nuts at the
horizontal-stabilizer-to-vertical-stabilizer attachment joints, and
replacement of discrepant parts.
Bombardier Repair Drawing (RD) 8/4-55-1143, Issue 2, dated
May 25, 2015. This service information describes procedures for
repairing corrosion and damage of the fitting bore.
This service information is reasonably available because the
interested parties have access to it through their normal course of
business or by the means identified in the ADDRESSES section.

Costs of Compliance

We estimate that this AD affects 54 airplanes of U.S. registry. We
estimate the following costs to comply with this AD:

Estimated Costs

Action
Labor cost
Parts cost
Cost per product
Cost on U.S. operators
Inspections (retained actions from AD 2016-24-03) 8 work-hours x $85 per hour = $680 $0 $680 $36,720
Sealing disk installation (new action) 4 work-hours x $85 per hour = $340 781 1,121 60,534
Replacement of DSC228 series barrel nuts (new action) 2 work-hours x $85 per hour = $170 2,236 2,406 129,924

We estimate the following costs to do any necessary replacements
that would be required based on the results of the inspection. We have
no way of determining the number of aircraft that might need these
replacements:

On-Condition Costs

Action
Labor cost
Parts cost
Cost per product
Replacement (retained action from AD 2016-24-03) 2 work-hours x $85 per hour = $170
$8,881
$9,051

We have received no definitive data that would enable us to provide
cost estimates for the other on-condition actions specified in this AD.

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.
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 transport category airplanes and associated
appliances to the Director of the System Oversight Division.

Regulatory Findings

We 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 the DOT Regulatory Policies
and Procedures (44 FR 11034, February 26, 1979);
3. Will not affect intrastate aviation in Alaska; 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)
2016-24-03, Amendment 39-18720 (81 FR 88623, December 8, 2016), and
adding the following new AD: