# De Havilland Canada Service Bulletin 84-27-74

Copy: Revision B ("84-27-74B"), 18 pages: PDF https://openairdocs.org/files/sha256/10/cd/10cd0430feba1f46e8f2834cbf913ea7077b3964ef7d2dc7493e593ca429a38f; text https://openairdocs.org/service-documents/bombardier/sb-84-27-74/file/10cd0430feba.md. Rights: © Bombardier Inc. Filed by the FAA in regulations.gov docket FAA-2021-0312; AD 2021-19-11 incorporates this document by reference. Not covered by OpenAirDocs’ CC0 dedication.

## Details

- Manufacturer: [Bombardier](https://openairdocs.org/service-documents/bombardier.md) (issued as De Havilland Canada)
- Type: Service bulletin (Service Bulletin)
- Number: 84-27-74
- Latest revision known: 84-27-74, Revision B, dated September 8, 2020 (OpenAirDocs)
- Page: https://openairdocs.org/service-documents/bombardier/sb-84-27-74

## ADs that cite it (1) (OpenAirDocs)

Newest first, with the revision each names, as OpenAirDocs read it from the AD's text.

- [AD 2021-19-11](https://openairdocs.org/ad/2021-19-11.md), effective Nov 18, 2021: Revisions A and B

Also cited in [1 proposed AD](https://openairdocs.org/service-documents/bombardier/sb-84-27-74/proposed.md).

## Text (18 pages)

Rights: © Bombardier Inc. Filed by the FAA in regulations.gov docket FAA-2021-0312; AD 2021-19-11 incorporates this document by reference. Not covered by OpenAirDocs’ CC0 dedication. Some pages are OCR from a scan. OCR can misread letters and numbers. Each page's text from the PDF; open the PDF at a page with #page=N.

### Page 1

Revision ‘B’ 08 Sep 2020 T x L t r S B 8 4 --- 2 7 --- 7 4
FQ
Page 1 of 2
D H C --- 8 ( D A S H 8 )
S E R V I C E B U L L E T I N 8 4 --- 2 7 --- 7 4
Flight Controls - - - Rudder Actuator Bracket Nuts - - - Inspection and
Rectification
This page transmits Revision ‘B’ of Service Bulletin 84- - -27- - -74, pages 1 thru
14 dated 08 Sep 2020.
This service bulletin is re- - -issued in its entirety for the reasons that follow:
--- T h eReferences section is revised to convey the latest revision of the
service bulletin and engineering documentation
--- T h eAccomplishment Instructions section is revised to make a changes to
Procedure, add a Warning, make a minor editorial change and add a NOTE.
--- R e v i s e dFigure 1 to correct washer part number from NAS1149D416J to
NAS1149D0416J
The Compliance recommendation in the previous issue of this service
bulletin is not affected by this revision. No additional rework to aircraft with
this service bulletin incorporated, is introduced by this revision.
Remove Service Bulletin 84- - -27- - -74 Revision ‘A’ dated 20 Jan 2020 and
replace with attached.
Previous issues of Service Bulletin 84- - -27- - -74:
Initial issue - - - Pages 1 thru 14 dated 20 Dec 2019
Revision ‘A’ - - - Pages 1 thru 14 dated 20 Jan 2020

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Revision ‘B’ 08 Sep 2020 T x L t r S B 8 4 --- 2 7 --- 7 4
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1

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FQRevision ‘B’ 08 Sep 2020
SERVICE BULLETIN
ATA SYSTEM: 2720 NUMBER: 84- - -27- - -74
DE HAVILLAND AIRCRAFT OF CANADA LIMITED (DHC) CONSIDERS
THIS SERVICE BULLETIN TO BE PARTICULARL Y SIGNIFICANT AND
URGES OPERATORS TO PROMPTL Y EVALUATE THE CONTENTS
SUBJECT : Flight Controls - - - Rudder Actuator Bracket Nuts - - - Inspection and
Rectification - - - ModSum 4- - - 114009
1. PLANNING INFORMA TION
A. Effectivity
Aircraft Affected:
In- - -Service: DHC- - -8 Aircraft Models 401 and 402 Serial Numbers 4001,
4003 thru 4609.
NOTE: The instructions in this service bulletin are only applicable to the
systems and parts installed at the time of delivery on the aircraft or as
changed by DHC Service Bulletin(s). Before you do this bulletin,
examine all STC or equivalent action changes to make sure this
bulletin can be completed.
Related ModSum Title
8Q113038 Flight Controls - - - Rudder Actuator Bracket Nuts,
Inspection and Rectification

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FQRevision ‘B’ 08 Sep 2020
Related ModSum Title
4Y124691 Flight Control - - - Rudder Actuator Instl - - - Actuator
Bracket Nuts Replacement
4D114014 Flight Controls - - - Rudder Actuator Mounting
Nuts Cracking
Spares Affected:
None
B. Reason
Problem: Operators have reported instances of cracked or missing nuts on the
vertical stabilizer rear spar rudder actuator brackets.
Solution: This service bulletin provides the instructions to do a detailed visual
inspection of the MS21042L4 nuts attaching the rudder actuator brackets
to the rear spar. If corrosion, cracks, or missing nuts are found, the
MS21042L4 nuts are replaced with NAS9926- - -4L nuts.
This service bulletin also provides th e necessary instructions if damage is
found. If required, MS21042L4 nuts are to be replaced with NAS9926- - -4L
nuts.
C. Description
The procedures in this service bulletin give the instructions to do the tasks that follow:
- - - Aircraft electrical power is removed
- - - The nose landing gear lock is engaged
- - - The main landing gear lock pins are installed through each main gear and main gear
door mechanism
- - - Rudder center hinge access panels are removed
- - - Eight rudder actuator bracket nuts on the rear spar are inspected
- - - If any nut is corroded, cracked, or missing, all eight nuts, bolts and associated
hardware are replaced
- - - Rudder center hinge access panels are installed

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- - - If required, a rudder system operational test is done
- - - Close out.
D. Compliance
DE HAVILLAND AIRCRAFT OF CANADA LIMITED highly recommends that ModSum
4- - -114009 be incorporated at the earliest opportunity unless otherwise directed by
the operator’s airworthiness authority.
Transport Canada Airworthiness Directive Pending.
E. Approval
The technical content of this service bulletin has been approved under the authority of
the Transport Canada Civil Aviation (TCCA) Design Approval Organization No: DAO
# 1 9 --- Q --- 0 1 .
This service bulletin does not affect Airworthiness Limitations (AWLs) or Damage
T olerance Inspections (DTIs).
F. M a n p o w e r
It will take an estimated 3.00 to 5.00 man- - -hours to complete this service bulletin. The
breakdown of the man- - -hours is shown in the table that follows:
TASK M A N --- H O U R S
J o b S e t --- U p 0.50
Procedure (Inspection) 1.00
Procedure (Rectification) 2.00
T e s t/R T S 1.00
Close- - -Out 0.50
This estimate is for direct labor done by an experienced crew and it does not include,
planning, familiarization, cure time, part fabrication, tool acquisition or lost time.

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G. Material - - - Price and Availability
Kit Number Description
8DK4354- - -001 Drawing Kit - - - Rudder Actuator Bracket
Nuts, Inspection and Rectification
Drawing Kit(s) (DKs) listed in the table above are drawings only. No parts will be
supplied.
The part(s) and material(s) required are listed in Paragraph 2.A. The parts required
may be either furnished or fabricated from the operator’s existing stock, purchased as
single items from DHC or purchased directly from industry sources. DK parts are to
be manufactured and approved locally (refer to disclaimer in the related text or
illustration). In some cases, an equivalen t to the DK part may be available from DHC
under the production part number shown as reference in Parts Required Per Aircraft.
See the contact information below.
DE HAVILLAND AIRCRAFT OF CANADA LIMITED
Material Services
123 Garratt Blvd.
To r o n t o
Ontario
Canada M3K- - -1Y5
DHC Phone Numbers :
North America:T oll Free: 1 (844)- - -CRC- - -CRC0 (1 (844) 272- - -2720) or
Direct: 1 (514) 855- - -8500
DHC Emails:
Parts: Europe, Middle East, Africa, and Russia: emear.parts@dehavilland.com
Americas and Rest of World: parts@dehavilland.com
If required the related 8DK drawings listed in the T able above can be requested by
writing to the e- - -mail address that follows:
dwg.request@dehavilland.com

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FQRevision ‘B’ 08 Sep 2020
H. T ooling - - - Price and Availability
None
I. Weight and Balance
Not affected
J. Electrical Load Data
Not affected
K. Publications Affected
Aircraft Illustrated Parts Catalog PSM 1- - -84- - -4......................
ModSums Manual PSM 1- - -84- - -12..................................
L. References
The revision ‘B’ of this service bulletin was prepared to the engineering drawings and
related data that follows:
DRAWING SHEET REV
8DK4354 1 A
ModSum 4Q114009 Rev. ‘C’
ModSum 4- - -114009 Rev. ‘D’
PCA 47463 Revision 0 (for internal reference only)
Transport Canada Airworthiness Directive Pending

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2. MATERIAL INFORMA TION
A. Parts Required Per Aircraft
(1) Drawing Kit 8DK4354- - -001
(2) Detailed Kit Content:
Quantity Per Kit
--- 0 0 1
Part Number Description Remarks
8 NAS1149D0416J Washer
8 NAS1149D0432J Washer
8 NAS6604- - -15 Bolt
8 NAS9926- - -4L Self Locking Nut
(3) In addition to the above parts, the following material is required for the
completion of this service bulletin and may be procured as single items from
DHC or purchased directly from industry sources.
Each consumable product listed in the table below is given its own unique
Product ID Number. The number is used to identify a particular recommended
product, the specifications and the trade names any of which can be used
unless specified otherwise (refer to PSM 1- - -84- - -18 Consumable Products
Manual).
Consumable
Product ID
Number
Qty. Per Aircraft Description Remarks
07- - -01C 1/2 Quart Compound, F13,
Corrosion Inhibit-
i n g C o a t i n g --- C o r -
rosion Preventive,
Clear, Soft Film
F13, Grade 2

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FQRevision ‘B’ 08 Sep 2020
B. Parts Required to Modify Spares
None
C. Special T ools and Equipment Required
Borescope equivalent to: ITI (Instrument T echnology Inc) Model 123010- - -40, (40
degrees with right angle adapter, 10 mm diameter 60 cm. long)
D. Existing Parts Accountability
The following parts may be affected by this service bulletin. Indented parts are
components of the next higher assembly. The quantity (Qty.) column lists the quantity
that may be affected per aircraft for non- - -indented parts and the quantity per next
higher assembly for indented parts.
Existing
Part Number Description Qty. IC DC
New Part
Number PNC
MS21042L4 Self Locking Nut 8 C DIS NAS9926- - -4L S
IC Interchangeability Code
A Not interchangeable.
B Removed Part. No direct replacement.
C Conditionally Interchangeable. Inst allation of superseded part negates the
intent of this service bulletin.
DC Disposition
DIS Discard Part.
MUI Multiple Usage Item: Return to stock if serviceable.
RWK Rework existing part in accordance with this service bulletin.
RWI Rework existing part per .....
SAL Salvage. Return to operator’s stores for salvage consideration.

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PNC Part Number Code
N No equivalent DHC part number for reworked part. Indicate on part that
this service bulletin has been accomplished.
R Part number after rework.
S Superseding or equivalent part number.
X Reworked part and superseding part are functionally and physically
equivalent but not identical.
3. ACCOMPLISHMENT INSTRUCTIONS
If it is not possible to complete all the instructions of this service bulletin because of the
configuration of the aircraft, speak with a representative of DHC in the CRC at 1 (844)
272- - -2720 (1 (844) CRC- - -CRC0) or email at thd@dehavilland.comfor analysis and to get an
approved disposition to complete this service bulletin.
A . J o b S e t --- U p
WARNING: MAKE SURE YOU INSTALL THE LOCKPINS ON THE MAIN LANDING
GEAR. MAKE SURE YOU ENGAGE THE NOSE GEAR LOCK. IF YOU
DO NOT DO THIS, THE LANDING GEAR CAN ACCIDENTALL Y
RETRACT . THIS CAN CAUSE INJURIES TO PERSONS AND
DAMAGE TO THE EQUIPMENT .
WARNING: MAKE SURE YOU INSTALL THE LOCKPINS IN THE DOOR
MECHANISMS OF THE MLG AND NLG. THE DOOR MECHANISMS
CAN ACCIDENTALL Y CLOSE THE LANDING GEAR DOORS. THIS
CAN CAUSE INJURIES TO PERSONS AND DAMAGE TO THE
EQUIPMENT .
(1) Remove pressure from the No. 1 and No. 2 hydraulic systems (refer to AMM
TASK 29- - -00- - -00- - -863- - -802).
(2) Placard and select all aircraft electrical power to OFF . Obey all relevant
W A R N I N G S a n d C A U T I O N S ( r e f e r t o A M M T A S K ’ S 2 4 --- 0 0 --- 0 0 --- 8 6 1 --- 8 0 2 a n d
24- - -00- - -00- - -910- - -801).
(3) Make sure that lock pins are installed through each main gear and main gear
door mechanism.
(4) Make sure the nose gear ground lock is engaged.
(5) Position suitable stand or lift to gain access to the inspection area.

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B. Procedure
(1) Move the FLAPS handle to 5 deg or greater. Have an assistant hold the rudder
pedals to full rudder- - -right.
(2) Push the rudder by hand to full right.
(3) Release the rudder pedals. Move the FLAPS handle to its original position.
WARNING: MAKE SURE AIRCRAFT IS INDOORS WITH HANGAR DOORS
CLOSED, OR CAREFULL Y BLOCK THE RUDDER WITH A SHOP AID
BETWEEN THE RUDDER AND THE VERTICAL STABILIZER FAIRING.
WIND GUSTS CAN MOVE THE RUDDER. THIS CAN CAUSE INJURIES
TO PERSONS AND DAMAGE TO THE EQUIPMENT .
(4) Remove the access panels 323BL and 323CL (refer to AMM TASK
20- - -50- - -55- - -000- - -801, drawing 8DK4354 sheet 1 flag note 6).
(5) Examine the visible ends of the rudder actuator bracket mounting nuts. Make
sure that there are no cracks, corrosion, missing nut or other damage (refer to
Figure 2).
NOTE: Use a light source, inspection mirror, magnifying glass and/or borescope
as necessary.
(6) If cracks, corrosion, missing nut, or other damage is found:
(a) Remove the access panels 322DL and 322DR (refer to applicable
i n s t r u c t i o n s i n A M M T A S K 2 7 --- 2 1 --- 2 6 --- 0 0 0 --- 8 0 1 a n d T A S K
20- - -50- - -55- - -000- - -801).
NOTE: It is not necessary to remove the actuators for rectification (nut
replacement).
(b) Replace fastener at each location with new nut NAS9926- - -4L, new bolt
NAS6604- - -15 and new washers NAS1149D0432J (under bolt head) and
NAS1149D0416J (under nut) (refer to Figure 1). Coat shank of bolt with
F13, Grade 2 compound (07- - -01C).
(c) Remove and install one nut and bolt at a time. T orque the nut to 70- - -80
l b f --- i n ( 7 . 9 --- 9 . 0 N --- m ) b e f o r e p r o c e e d i n g t o n e x t f a s t e n e r l o c a t i o n ( r e f e r t o
AMM TASK 20- - -10- - -01- - -430- - -801). All eight nuts and bolts must be
replaced.
(d) Install the access panels 322DL and 322DR (refer to applicable instructions
in AMM TASK 27- - -21- - -26- - -400- - -801 and TASK 20- - -50- - -55- - -400- - -801).
(1) If installed, remove any shop aid blocking the rudder.

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(e) Do an operational test of the rudder control system (refer to AMM TASK
27- - -20- - -00- - -710- - -802).
(7) If no cracks, corrosion, missing nuts or other damage is found in any existing nuts
MS21042L4, the undamaged nuts and all other hardware can remain in service.
NOTE: At the operator’s discretion it is acceptable to replace all eight nuts even if
no missing nuts or damage is found.
(8) Install the access panels 323BL and 323CL (refer to AMM TASK
20- - -50- - -55- - -400- - -801).
C. Close Out
(1) Remove all tools and equipment from the work area.
(2) Complete the enclosed inspection forms (Appendix A) with inspection results
and submit to the T echnical Help Desk.
(3) On completion of this service bulletin, make the following entry in the appropriate
logbooks: “Service Bulletin 84- - -27- - -74 {Flight Controls - - - Rudder Actuator
Bracket Nuts - - - Inspection and Rectification - - - ModSum 4- - -114009}
accomplished.”

### Page 13 (OCR)

SERVICE BULLETIN 84-27-74
J
NAS9926 - 4L
NAS6604 - 15
NAS1149D0432J  QTY. x4
(UNDER BOLT HEAD)
NAS1149D0416J
(UNDER NUT)
FITTING  TUATOR ARU
ASSEMBLY UPPER
ACTUATOR BRACKET
REAR
SPAR ASSEMBLY  NAS9926 - 4L
NAS6604 - 15
NAS1149D0432J  QTY. x4
(UNDER BOLT HEAD)
NAS1149D0416J
FITTING  (UNDER NUT)
ASSEMBLY LOWER
*ACTUATOR BRACKET
-_.
YO. O
LOOKING FORWARD ON REAR SPAR-RIGHT SIDE  cg5675a01.dg. aj. may24/2019
RUDDER AND ACTUATOR ARM
NOT SHOWN FOR CLARITY
Rudder Actuator Bracket
Figure 1
S.B. 84-27-74
20 Dec 2019
Revision 'B' 08 Sep 2020  Page 11 of 14
FQ

### Page 14 (OCR)

SERVICE BULLETIN 84-27-74
— NUT
CRACK-
LOCATION TO CHECK FOR CORROSION AND CRACK
05675a0 2dg, al, mav24/2019
Rudder Actuator Bracket Mounting Nut
Figure 2
S.B. 84-27-74
0 Dec 201  evision 'B' 08 Sep 202  Page 12 of 14
FQ

### Page 15 (OCR)

SERVICE BULLETIN 84-27-74
APPENDIX A
Date of inspection:
Rudder Actuator Installation
Aircraft  Hours  Cycles  Upper Fitting Assembly  Lower Fitting Assembly
S/N  Self Locking  Self Locking  Self Locking  Self Locking
Nut Cracked  Nut Corroded  Nut Cracked  Nut Corroded
Yes  NO  Yes  No  Yes  No  Yes  No
Inspection Form  cg5675a03.dg, aj, may24/2019
S.B. 84-27-74
20 Dec 2019
Revision 'B' 08 Sep 2020  Page 13 of 14
FQ

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This Page Intentionally Blank.

### Page 17

Oct 2019
SERVICE BULLETIN (SB) - - - RECORD OF INCORPORATION
DASH 8 AIRCRAFT
To : CMDB Focal
Email: cmdb.request@dehavilland.com
From:
Company:
Phone: Extn:
Facsimile: Date:
Email:
The data that you provide below will help us record the incorporation of this Service
Bulletin and the aircraft effectivity in the maintenance manual.
Operator: Service Bulletin: __________________ Revision: _________
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Aircraft Serial Number: Model Number: Date Bulletin Completed:
Email PDF to:
cmdb.request@dehavilland.com

### Page 18

Oct 2019
SERVICE BULLETIN (SB) - - - COMMENT SHEET - - - DASH 8 AIRCRAFT
To : SB Focal, DE HAVILLAND AIRCRAFT OF CANADA LIMITED
Phone: 1 (416) 373 - - -5098
Email: george.moffatt@dehavilland.com
From:
Company:
Phone: Extn:
Facsimile: Date:
Email:
Select appropriate box(es) and add comments or suggestions you would like us to know
that may enhance the quality of our service bulletins.
Service Bulletin: Revision: ModSum:
1. PLANNING INFORMATION
V Effectivity V Reason V Description V Compliance
V Approval V Manpower V Material V Weight and Balance
V Electrical Load V T ooling V References V Publications Affected
2. MATERIAL INFORMATION
V Kit Content V Special T ools/Equipment V Parts to Modify Spares
V Consumables V Disposition of Existing Parts V Other
3. ACCOMPLISHMENT INSTRUCTIONS
V J o b S e t --- U p V Procedure V Close- - -Out V Te s t
V Illustration(s) V Other
4. COMMENTS, REMARKS, SUGGESTIONS
Email PDF to:
george.moffatt@dehavilland.com

---
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