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Revision ‘A’ 04 Oct 2013 DHC-8 (DASH 8) SERVICE BULLETIN 84-32-122 Landing Gear - Nose Wheel Steering - Addition of Pull Down Resistors to Pilot Hand Control (PHC) and Rudder Pedal Potentiometer - ModSum 4-126585 This page transmits Revision ‘A’ of Service Bulletin 84-32-122, pages 1 thru 14 dated 04 Oct 2013.
This service bulletin is re-issued in its entirety for the reasons that follow:
-t h e References section is revised to convey the latest revision of the service bulletin and engineering documentation -t h e Figures 3 and 4 are revised to add a NOTE stating that the figures were taken from drawing 8Z9652 and to refer to the drawing for additional details.
The Compliance in the previous issues of this service bulletin is not affected by this revision. No additional rework to the aircraft is introduced by this revision.
Remove the previous revision of Service Bulletin 84-32-122 and replace with attached.
Previous issue(s) of Service Bulletin 84-32-122:
Initial issue - Pages 1 thru 14 dated 28 Aug 2013
No text on this page: it may be a figure. Open the PDF to see it.
D S.B. 84-32-122 Page 1 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013
SERVICE BULLETIN Customer Support ATA SYSTEM: 3251 NUMBER: 84-32-122 SUBJECT: Landing Gear - Nose Wheel Steering - Addition of Pull Down Resistors to Pilot Hand Control (PHC) and Rudder Pedal Potentiometer - ModSum 4-126585
1. PLANNING INFORMATION A. Effectivity Aircraft Affected:
In-Service: DHC-8 Aircraft Models 401 and 402 Serial Numbers 4001 and 4003 thru 4448.
Production: ModSum 4-123898 will be installed before delivery on applicable DHC-8 Aircraft at Serial Numbers 4449 and subsequent.
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 Bombardier Aerospace Service Bulletin(s). Before you do this bulletin, examine all STC or equivalent action changes to make sure this bulletin can be completed.
Spares Affected:
None
SERVICE BULLETIN 84-32-122 S.B. 84-32-122 Page 2 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013 B. Reason Problem: The possibility of uncommanded, un-annunciated and erratic steering exists with the potential to cause runway/taxiway excursion.
Cause: If there is open circuit between the Pilot Hand Control (PHC) Potentiometer and the Steering Control Unit (SCU) and/or between the Rudder Pedal Potentiometer and the SCU, the fault may not detected and not annunciated on the caution warning panel. With an open circuit in the wiring between the PHC or Rudder and SCU, the nosewheel may rotate at a high rate. It may rotate left or right over a 40 ˚ a n g l ef o rt h eP H Ca n d8˚ for the Rudder and remain at that angle with the nose wheel not going into free castor mode.
The root of the problem is inherent to the design of the SCU and test has shown it takes excessive time for an open circuit to be detected by the SCU. The voltage drop in the SCU circuitry may not be sufficiently fast enough before the nose wheel rotates to a severe angle. A sustained open circuit between the SCU and PHC or Rudder potentiometer may cause an uncommanded, un-annunciated hard over steering event. This may lead to loss of directional control and potential taxiway/runway excursion. The intermittent steering may also occur and is manifested by erratic steering input signal.
Solution: This service bulletin incorporates ModSum 4-126585.
The ModSum installs a pull-down resistor that effectively trips the PHC or rudder range monitor, reverting to fail safe free-castor mode, in the event there is an open circuit between the PHC and rudder pedal potentiometers and the SCU.
C. Description The procedures in this service bulletin give the instructions to do the tasks that follow:
- all aircraft electrical power systems are selected to OFF
- the nose landing gear lock is engaged
SERVICE BULLETIN 84-32-122 S.B. 84-32-122 Page 3 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013
- the main landing gear lock pins are installed thru each main gear and main gear door mechanism
- access panels 112AR and 122AR are removed
- flight crew oxygen cylinder is removed as necessary
- existing wires from connector pins of connector ends 3251-P1 and 9811-P2 are removed
- continuity and resistance checks between pins are done before installation of new harnesses
- new wire harnesses are installed
- continuity and resistance checks of wire harnesses between connector ends 3251-P1 and 9811-P2 are done
- functional test (open circuit test) of the nose wheel steering control system is done
- flight crew oxygen cylinder is installed if removed
- access panels 112AR and 122AR are installed
- close out.
D. Compliance Bombardier Inc. recommends incorpora tion of ModSum 4-126585 at the earliest opportunity unless otherwise directed by the operator’s airworthiness authority.
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 #93-Q-02.
This service bulletin does not affect Airworthiness Limitations (AWLs) or Damage Tolerance Inspections (DTIs).
SERVICE BULLETIN 84-32-122 S.B. 84-32-122 Page 4 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013 F. Manpower It will take an estimated 5.5 man-hours to complete this service bulletin. The breakdown of the man-hours is shown in the table that follows:
TASK MAN-HOURS Job Set-Up 1.00 Procedure 3.00 Test / RTS 1.00 Close-Out 0.50 For any on-site labor assistance, please speak with a Fleet Services representative for a quote. The Fleet Services group can be contacted via the Q Series Technical Help Desk by telephone at 416-375-4000 or email at:
thd.qseries@aero.bombardier.com.
G. Material - Price and Availability The ModKit required to do this service bulletin are listed in the table below:
Operators should submit a purchase orde r through the Customer Accounts Service Team (CAST) at Bombardier Aerospace Regional Aircraft division specifying aircraft serial number(s) to:
Bombardier Aerospace Customer Accounts Services Team (Mail Stop N11-32) 123 Garratt Blvd.
Toronto Ontario Canada M3K-1Y5 Facsimile: (416) 375-3060 Telephone: (416) 375-3920 Facsimile:
International: (416) 375-3334
SERVICE BULLETIN 84-32-122 S.B. 84-32-122 Page 5 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013 European: (416) 373-5966 Americas East: (416) 373-5964 Americas West: (416) 373-5965 Telephone:
International: (416) 375-3706 European: (416) 373-3704 Americas East: (416) 375-3700 Americas West: (416) 373-5888 E-mail addresses:
International: cast.international@aero.bombardier.com European: cast.europe@aero.bombardier.com Americas East: cast.americaseast@aero.bombardier.com Americas West: cast.americaswest@aero.bombardier.com Kit Number Description 8MK4664 Rework Kit - NWS Addition of Resistor H. Tooling - Price and Availability None I. Weight and Balance A/C Type and Model Weight (Lb) Arm (Inches) Moment (Inches x Lb) x 0.001 DHC-8 Model 401/402 +0.37 -108.70 -0.04 J. Electrical Load Data Not affected
SERVICE BULLETIN 84-32-122 S.B. 84-32-122 Page 6 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013 K. Publications Affected Maintenance Manual PSM 1-84-2................................
Wiring Diagrams Manual PSM 1-84-2W............................
Dash 8 Illustrated Parts Catalogue PSM 1-84-4....................
ModSums Manual PSM 1-84-12..................................
Weight and Balance Manual (Imperial) PSM 1-84-8................
Weight and Balance Manual (Metric) PSM 1-84-8M..................
L. References Revision ‘A’ of this service bulletin was prepared to the engineering drawings and related data that follows:
DRAWING SHEET REV 8MK4664 1 -- 8Z9652 1 A ModSum 4Q126585 Rev. ‘B’ ModSum 4-126585 Rev. ‘B’ ModSum 4Y123898 Rev. ‘B’ ModSum 4-123898 Rev. ‘B’ PCA 44578 Revision 0 (for internal reference only)
2. MATERIAL INFORMATION A. Parts Required Per Aircraft
(1) Modification Kit 8MK4664-001
SERVICE BULLETIN 84-32-122 S.B. 84-32-122 Page 7 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013
(2) Detailed Kit Content:
Quantity Per Kit -001 Part Number Description Remarks 3 B0816063-003 Solder Sleeve See NOTE below 14 B0816063-002 Solder Sleeve See NOTE below 23 B0816063-001 Solder Sleeve See NOTE below 1 8Z9652-013 Cable Assy 1 8Z9652-011 Cable Assy NOTE: These are additional sleeves included in the kit which may be used in the event existing sleeves are damaged during disassembly.
B. Parts Required to Modify Spares None C. Special Tools and Equipment Required None D. Existing Parts Accountability None
3. ACCOMPLISHMENT INSTRUCTIONS A. Job Set-Up
(1) Placard and select all aircraft electrical power to OFF. Obey all relevant WARNINGS and CAUTIONS (refer to AMM TASKs 24-00-00-861-802 and 24-00-00-910-801).
(2) Make sure the nose gear ground lock is engaged.
(3) Make sure that lock pins are installed thru each main gear and main gear door mechanism.
(4) Set wheel chocks in front and behind the landing gear tires.
SERVICE BULLETIN 84-32-122 S.B. 84-32-122 Page 8 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013
(5) Remove access panels 112AR and 122AR (refer to AMM TASK 06-41-00-992-801 for locations and to AMM TASK 53-11-00-000-801 for applicable instructions).
(6) For better access, remove the flight crew oxygen cylinder as necessary (refer to AMM TASK 35-11-01-000-801 or TASK 35-11-01-000-802).
B. Procedure
(1) Locate connector ends 3251-P1 at the lower right side of the nose compartment bay and 9811-P2 at RHS fwd pressure bulkhead (refer to Figure 2).
(2) Remove clamps. tie wraps and straps from existing wiring harnesses as necessary.
(3) Remove the shield pigtails from backshell of connectors 3251-P1 and 9811-P2 and the wires from connector pins of connector 3251-P1 and 9811-P2 as follows (refer to applicable instructions in WDM 20-12-10-201 and Figure 3):
From Pin Wire Code To Pin 3251-P1 35 W20A-22-6/BLK 9811-P2 A- 3251-P1 34 W20A-22-6/WHT 9811-P2 B- 3251-P1 36 W20A-22-6/RED 9811-P2 C- 3251-P1 27 W21A-22-6/BLK 9811-P2 D- 3251-P1 28 W21A-22-6/WHT 9811-P2 E- 3251-P1 29 W21A-22-6/RED 9811-P2 F-
(4) Tape and stow connector end 3251-P1 wire pins 27, 28, 29, 34, 35, 36 and shield pigtail and connector end 9811-P2 wire pins A, B, C, D, E, F and shield pigtail for future use.
NOTE: Do not damage or cut wire pins as they will be used for future re-installation.
SERVICE BULLETIN 84-32-122 S.B. 84-32-122 Page 9 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013
(5) Before installation of the new cable assemblies, do continuity and resistance checks between the connector pins with an ohmmeter to verify compliance with the schematic wiring view shown on drawing 8Z9652, POST CONDITION NEW WIRING.
NOTE: Continuity of a circuit is affected when a resistor is part of a circuit. When checking continuity across a resistor the value of the resistor must be observed. Per dwg 8Z9652, resistors R2 and R3 are at 2 megaohms +/- 1% tolerance.
(6) If the resistance exceeds 5 ohms from point to point (open circuit), recheck the new and reworked wiring to make sure it is terminated to the correct connection, check the wiring for mechanical damage, loose connector parts, bent pins and corrosion. Correct the deficiency.
(7) Prior to installation of the new cable assemblies do an electrical continuity measurement from shield pigtail at 9811-P2 to shield pigtail at 3251-P1 using a low resistance digital multimeter (four wire bonding meter). Reading should be less than 100 milliohms. If the reading exceeds 100 milliohms check the shield continuity across shield splices of the wire.
(8) Insert new cable assembly pins to appropriate connector ends (refer to Figures 2 and 4 and applicable instructions in WDM 20-12-10-201).
NOTE: The individual wire shields are grounded by placing the jumper wire from the solder sleeves, around the grounding adaptor ring of the backshell per WDM 20-15-10-401.
(9) Reinstall clamps, tie wraps and straps as necessary to secure the wiring harnesses (refer to applicable instructions in WDM 20-12-10-201).
NOTE: It is acceptable to increase clamp size to accommodate new cable assemblies. Do not tie wrap or clamp over the middle of resistors R2 and R3 due to longer flexible tube and make sure the splices are placed against rigid surface or area. It is permissible to have end of tube under clamp.
SERVICE BULLETIN 84-32-122 S.B. 84-32-122 Page 10 of 14 28 Aug 2013 NB Revision ‘A’ 04 Oct 2013
(10) After installation, do continuity and resistance checks of the wire harnesses between connector ends 3251-P1 and 9811-P2 with an ohmmeter to verify compliance with the schematic wiring view shown on Figure 4, POST CONDITION NEW WIRING.
NOTE: Continuity of a circuit is affected when a resistor is part of a circuit. When checking continuity across a resistor the value of the resistor must be observed. Per dwg 8Z9652, resistors R2 and R3 are at 2 megaohms +/- 1% tolerance.
(11) If the resistance exceeds 5 ohms from point to point (open circuit), recheck the new and reworked wiring to make sure it is terminated to the correct connection, check the wiring for mechanical damage, loose connector parts, bent pins and corrosion. Correct the deficiency.
C. Close Out
(1) Do the functional test (open circuit test) of the nose wheel steering control system in accordance with the instructions given in drawing 8Z9652.
(2) If removed, install the flight crew oxygen cylinder (refer to AMM TASK 35-11-01-400-801 or TASK 35-11-01-400-802).
(3) Install access panels 112AR and 122AR (refer to AMM TASK 06-41-00-992-801 for locations and to AMM TASK 53-11-00-400-801 for applicable instructions).
(4) Remove all tools and equipment from the work area.
(5) On incorporation of this ModSum, make an entry that conforms to local regulatory requirements in the applicable logbook(s). Enter component serial numbers if applicable. Enter this ModSum number only after complete and functional incorporation of all work defined in this service bulletin.