# De Havilland Canada Service Bulletin 8-27-121

Copy: No revision named ("SB 8-27-121"), 14 pages: PDF https://openairdocs.org/files/sha256/a4/f1/a4f1ce0a76711084b2e5992224cd380475eb751fb31532e6bc0ea8309c8d6754; text https://openairdocs.org/service-documents/bombardier/sb-8-27-121/file/a4f1ce0a7671.md. Rights: © Bombardier Inc. Filed by the FAA in regulations.gov docket FAA-2025-2558; AD 2026-11-06 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: 8-27-121
- Page: https://openairdocs.org/service-documents/bombardier/sb-8-27-121

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

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

- [AD 2026-11-06](https://openairdocs.org/ad/2026-11-06.md), effective Jul 9, 2026: No revision named

Also cited in [1 proposed AD](https://openairdocs.org/service-documents/bombardier/sb-8-27-121/proposed.md).

## Text (14 pages)

Rights: © Bombardier Inc. Filed by the FAA in regulations.gov docket FAA-2025-2558; AD 2026-11-06 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

S . B . 8 --- 2 7 --- 1 2 1
Page 1 of 1230 Jul 2019
PS/JV
SERVICE BULLETIN
Customer
Support
ATA SYSTEM: 2720 NUMBER: 8- - -27- - -121
DE HAVILLAND AIRCRAFT OF CANADA LIMITED (DHC) CONSIDERS
URGES OPERATORS TO PROMPTL Y EVALUATE THE CONTENTS
THIS SERVICE BULLETIN TO BE PARTICULARL Y SIGNIFICANT AND
SUBJECT : Flight Controls - - - Rudder Control Installation - - - Front Fuselage - - -
Special Inspection of Barrel Nuts for Pedal Adjustment Mechanism
1. PLANNING INFORMA TION
A. Effectivity
Aircraft Affected:
In- - -Service: DHC- - -8 Aircraft Models 102, 103, 106, 201, 202, 301, 311, 314
and 315 Serial Numbers 003 thru 672.
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.

### Page 2

S E R V I C E B U L L E T I N 8 --- 2 7 --- 1 2 1
S . B . 8 --- 2 7 --- 1 2 1
Page 2 of 1230 Jul 2019
PS/JV
Spares Affected:
None
B. Reason
Problem: Corrosion or cracks have been reported in DSC228- - -type barrel nuts in the
fleet. Four DSC228- - -4 barrel nuts are installed in the rudder pedal
adjustment mechanism assemblies.
Solution: This service bulletin provides the instructions to do a detailed visual
inspection of the barrel nuts DSC228- - -4 used in the rudder pedal
adjustment mechanism to look for any corrosion or cracks.
This service bulletin also provides th e necessary instructions if damage is
found. If required, barrel nuts DSC228- - -4 are to be replaced with
B0203073- - -4.
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
- - - lower- - -side front- - -fuselage access panels are removed
- - - four barrel nuts in the rudder pedal adjustment mechanism are inspected
- - - if any barrel nut is cracked or corroded, replace with new barrel nut and associated
hardware
- - - lower- - -side front- - -fuselage access panels are installed
- - - close out.
D. Compliance
DE HAVILLAND AIRCRAFT OF CANADA LIMI TED highly recommends this special
inspection service bulletin be incorporated at the earliest opportunity unless otherwise
directed by the operator’s airworthiness authority.
A Transport Canada Airworthiness Directive is Pending.

### Page 3

S E R V I C E B U L L E T I N 8 --- 2 7 --- 1 2 1
S . B . 8 --- 2 7 --- 1 2 1
Page 3 of 1230 Jul 2019
PS/JV
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
# 9 3 --- Q --- 0 2 .
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 labour done by an experienced crew and it does not
include, planning, familiarization, cure tim e, part fabrication, tool acquisition or lost
time.
G. Material - - - Price and Availability
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.
H. T ooling - - - Price and Availability
Part Number Description Remarks
GSB2700006 Rigging Pin Set

### Page 4

S E R V I C E B U L L E T I N 8 --- 2 7 --- 1 2 1
S . B . 8 --- 2 7 --- 1 2 1
Page 4 of 1230 Jul 2019
PS/JV
I. Weight and Balance
Not affected
J. Electrical Load Data
Not affected
K. Publications Affected
Aircraft Illustrated Parts Catalog PSM 1- - -8- - -4 and......................
P S M 1 --- 8 2 --- 4 a n d
P S M 1 --- 8 3 --- 4
Modifications Manual PSM 1- - -813- - -12................................
L. References
The initial issue of this service bulletin was prepared to the engineering drawings and
related data that follows:
PCA 08234 Revision 0 (for internal reference only)
ModSum 8Q110206 Rev. ‘A’
A Transport Canada Airworthiness Directive is Pending.
2. MATERIAL INFORMA TION
A. Parts Required Per Aircraft
(1) Detailed Parts List:

### Page 5

S E R V I C E B U L L E T I N 8 --- 2 7 --- 1 2 1
S . B . 8 --- 2 7 --- 1 2 1
Page 5 of 1230 Jul 2019
PS/JV
Quantity
Per Aircraft
Part Number Description Remarks
4
4
4
4
B0203073- - -4
NAS578- - -4A
MS20004- - -8
MS20002C4
Barrel Nut
Retainer
Bolt
Washer
NOTE: This service bulletin is self- - -contained. No drawings will be supplied.
(2) In addition to the above part(s), the f ollowing consumable products are 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 “REF
ITEM” identification number that is used to identify a particular recommended
product, the specifications and the trade names any of which can be used
u n l e s s s p e c i f i e d o t h e r w i s e ( r e f e r t o P S M 1 --- 8 --- 2 , 1 --- 8 2 --- 2 o r 1 --- 8 3 --- 2 A i r c r a f t
Maintenance Manual (AMM) Chapter 51- - -31- - -00 CONSUMABLE MATERIALS - - -
MAINTENANCE PRACTICES).
REF ITEM Qty. Per Aircraft Description Remarks
07- - -01 1/2 Quart F 1 3 C o a t i n g ---
Compound, Corro-
sion Preventive,
(hard, soft film,
moisture displac-
ing)
F13, Grade 2
B. Parts Required to Modify Spares
None

### Page 6

S E R V I C E B U L L E T I N 8 --- 2 7 --- 1 2 1
S . B . 8 --- 2 7 --- 1 2 1
Page 6 of 1230 Jul 2019
PS/JV
C. Special T ools and Equipment Required
Borescope equivalent to: ITI (Instrument T echnology Inc) Model 123010- - -40, (40
degrees with right angle adapter, 10mm 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
DSC228- - -4 Barrel Nut 4 C DIS B0203073- - -4 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.

### Page 7

S E R V I C E B U L L E T I N 8 --- 2 7 --- 1 2 1
S . B . 8 --- 2 7 --- 1 2 1
Page 7 of 1230 Jul 2019
PS/JV
PNC Part Number Code
N No equivalent Bombardier Inc. 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. klshdfksldhf
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) 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 P S M 1 --- 8 --- 2 o r 1 --- 8 2 --- 2 o r 1 --- 8 3 --- 2
Chapters 12 and 24).
(2) Make sure that lock pins are installed through each main gear and main gear
door mechanism.
(3) Make sure the nose gear ground lock is engaged.

### Page 8

S E R V I C E B U L L E T I N 8 --- 2 7 --- 1 2 1
S . B . 8 --- 2 7 --- 1 2 1
Page 8 of 1230 Jul 2019
PS/JV
B. Procedure
(1) Remove lower- - -side front- - -fuselage access panels 121AL and 122AR.
(2) Install the rigging pin in the left for ward rudder quadrant (refer to Figure 1).
(3) If necessary for access, remove the rudder- - -pedal cover assembly (refer to Figure
1 and applicable instructions in AMM 27- - -20- - -02- - -02 or AMM TASK
27- - -20- - -00- - -020- - -801).
(4) Examine both upper and lower visible ends of the barrel nuts. Make sure that
there are no cracks, corrosion or other types of damages.
NOTE: Use a light source, inspection mirror, magnifying glass and/or borescope
as necessary.
(5) If cracks, corrosion or other damage is found in any barrel nut:
(a) Remove the rudder potentiometer link for access (refer to AMM
27- - -20- - -00- - -02 or AMM TASK 27- - -20- - -00- - -830- - -801).
(b) Install a rigging pin in the right for ward rudder quadrant (refer to Figure 1).
(c) Replace existing barrel nut DSC228- - -4 with new barrel nut B0203073- - -4,
new retainer NAS578- - -4A, new bolt MS20004- - -8 and new washer
MS20002C4. Coat shank of bolt with F13, Grade 2 (07- - -01).
(d) Remove the rigging pin in the right forward rudder quadrant.
(e) Install the rudder potentiometer link (refer to AMM 27- - -20- - -00- - -02 or AMM
TASK 27- - -20- - -00- - -830- - -801).
(f) Check rigging of the rudder potentiometer (refer to AMM 32- - -50- - -00- - -02 or
AMM TASK 32- - -50- - -00- - -820- - -801).
(6) If no cracks, corrosion or other damage is found in any existing barrel nuts
DSC228- - -4, the undamaged barrel nuts and all other hardware will remain in
service.
(7) Remove the rigging pin in the left forward rudder quadrant.
(8) If removed, install the rudder- - -pedal cover assembly (refer to Figure 1 and
applicable instructions in AMM 27- - -20- - -02- - -02 or AMM TASK
27- - -20- - -00- - -400- - -801).
(9) Do an operational test of the rudder control system (refer to AMM 27- - -20- - -00- - -02
or AMM TASK 27- - -20- - -00- - -710- - -801).
(10) Install lower- - -side front- - -fuselage access panels 121AL and 122AR.

### Page 9

S E R V I C E B U L L E T I N 8 --- 2 7 --- 1 2 1
S . B . 8 --- 2 7 --- 1 2 1
Page 9 of 1230 Jul 2019
PS/JV
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 8- - -27- - -121 {Flight Controls - - - Rudder Control
Installation - - - Front Fuselage - - - Special Inspection of Barrel Nuts for Pedal
Adjustment Mechanism} accomplished.”

### Page 10 (OCR)

SERVICE BULLETIN 8-27-121
RUDDER-PEDAL
COVER ASSEMBLY
RIGGING
PIN
RETAINER
BARREL NUT
PEDAL
ADJUSTMENT
LEVER
WASHER
BOLT
NOTE  dsb8_27121_001.dg. rs/nn, mar11/2019
Left side shown.
Right side opposite.
Mechanism Assembly - Rudder Pedal Adjustment
Figure 1 (Sheet 1 of 2)
S.B. 8-27-121
30 Jul 2019
Page 10 of 12
PS/JV

### Page 11 (OCR)

SERVICE BULLETIN 8-27-121
CHECK FOR
CORROSION AROUND A
THIS AREA
NUf
CRACK
LOCATION TO CHECK FOR CORROSION AND CRACK  dste_27 121_002dg, ev, mar11/2019
NOTE
A Nut installed on aircraft with this
surface facing inboard.
Mechanism Assembly - Rudder Pedal Adjustment
Figure 1 (Sheet 2 of 2)
S.B. 8-27-121
30 Jul 2019
Page 11 of 12
PS/JV

### Page 12 (OCR)

SERVICE BULLETIN 8-27-121
APPENDIX A
Date of inspection:
Pilot's Rudder Pedal Adjustment Lever
Aircraft  Hours  Cycles  Forward Barrel Nut  Aft Barrel Nut
S/N  Barrel Nut  Barrel Nut  Barrel Nut  Barrel Nut
Cracked  Corroded  Cracked  Corroded
Yes  No  Yes  No  Yes  No  Yes  No
Date of inspection:
Co-pilot's Rudder Pedal Adjustment Lever
Aircraft  Hours  Cycles  Forward Barrel Nut  Aft Barrel Nut
S/N  Barrel Nut  Barrel Nut  Barrel Nut  Barrel Nut
Cracked  Corroded  Cracked  Corroded
Yes  No  Yes  No  Yes  No  Yes  No
dsb8_27121_003.dg. nn, apr22/2019
Inspection Form
30 Jul 2019  S.B. 8-27-121
Page 12 of 12
PS/JV

### Page 13

Jul 2019
SERVICE BULLETIN (SB) - - - RECORD OF INCORPORATION
- - - Q SERIES 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 ModSum
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 14

Jun 2019
SERVICE BULLETIN (SB) - - - COMMENT SHEET - - - Q SERIES 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

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain, except the copies of manufacturers’ service documents, which belong to their rights holders.