Bombardier (Boeing Canada/De Havilland) DHC-8 Series Aeroplanes
AD/DHC-8/8
Amdt 4
Flap Drive and Torque Sensing Systems 11/94
Applicability: Model DHC-8 series, serial numbers 3 and subsequent, as indicated.
Requirement: Part I. For aircraft serial numbers 3 through 177, and serial numbers 178 through 231, 233, 235, 237, and 243:
- (a) Locate flap primary-drive torque tubes having part numbers and serial numbers listed in revised table 1 below:
TABLE 1
TORQUE TUBE P/N SERIES TORQUE TUBE S/N
734187 125 through 171
734378 129 through 150
734380 127 through 166
734382 211 through 322
734384 153 through 188 and 226 through 235
734386 195 through 286
734388 160 through 177
(b) Determine whether torque tubes located by 1.(a) above have been re-identified with the service bulletin number indicated in Table 2 below.
Note: For re-identification, the applicable service bulletin number may have been marked on the rod with indelible ink or on the identification plate adjacent to the part number.
(i) Torque tubes found to have been re-identified with the applicable service bulletin number do not require further action per Part 1 of this Directive.
(ii) Torque tubes not re-identified with the applicable service bulletin number must be inspected and reworked as required by Part I, Requirements 1(c) and (d), and 2 below.
(c) On the torque tubes located per Requirement 1.(b)(ii) above, remove the through bolt from the splined coupling(s) of each torque tube and, using a 10x magnifying glass, visually inspect the area around all holes for cracks.
Note: Some torque tubes have one splined coupling, while others have two. If a splined coupling is found cracked, accomplish one of the following steps before further flight:
(i) Replace the splined coupling(s) in accordance with the accomplishment instructions in the appropriate Sundstrand service bulletin (see Table 2). Re-identify the torque tubes as indicated in the service bulletins.
Marking the service bulletin number on the rod with indelible ink will satisfy this requirement; or,
(ii) Replace the particular torque tube with a serviceable unit.
| TABLE 2 |
|
Torque Tube P/N Series | Sunstrand SB NO | Post-Mod Identification |
734187 | 734187-27-A2 Revision 1 | 27-A2 |
734378 | 734378-27-A3 Revision 1 | 27-A3 |
734380 | 734380-27-A2 Revision 1 | 27-A2 |
734382 | 734380-27-A3 Revision 1 | 27-A3 |
734384 | 734384-27-A2 Revision 1 | 27-A2 |
734386 | 734386-27-A2 Revision 1 | 27-A2 |
734388 | 734388-27-A1 Revision 1 | 27-A1 |
(d) Upon reassembly, install the through bolt and torque to between 20 and 25 in- lb.
2. Unless already accomplished per Part I, Requirement 1.(c); replace all splined couplings on torque tubes located per Part I, Requirement 1.(b)(ii) above, in accordance with the accomplishment instructions in the appropriate Sundstrand service bulletin (Table 2). Re-identify the torque tubes as indicated in the service bulletins. Marking the service bulletin number on the rod with indelible ink will satisfy this requirement.
Part II. For aircraft serial numbers 3 through 293:
- Accomplish the following visual inspection of the flap primary-drive torque tube system and the flap secondary-drive flex shaft system:
(a) Extend flaps fully.
(b) Visually inspect the flap primary-drive torque tubes over their entire length for fracture, rubbing and wear.
(c) Torque tubes must be replaced before further flight if wear exceeds 0.25mm (0.010 inch) in depth or is present over more than 180 degrees around the circumference of the shafts.
(d) Visually inspect the flap secondary-drive flex drive for permanent deformation (kinks), or evidence of excessive heat (blueing of outer braided sheath, melting of outer plastic sheath, loss of blue anodic film on the casing ferrules).
(e) Damaged flex shafts must be replaced with serviceable flex shafts before further flight.
2. Accomplish the following:
(a) Perform an operational check of the torque sensor as per maintenance program task 2750/11. Refer to DASH 8 Maintenance Program Supplementary Information, PSM 1-8-7/1-83-7, Volume 2, Procedures-27.
(b) Any torque sensor found malfunctioning or jammed must be replaced with a serviceable unit before further flight.
Note: The inspections required by Part II, Requirements 1 and 2 above may be terminated on aircraft that have complied with Part III of this Directive and which have incorporated both of the Boeing Canada/de Havilland modifications listed below:
(i) Modification No. 8/1473, Service Bulletin No. 8-54-16, ‘Nacelles - Flap Torque Tube - Introduction of Torque Tube Guard’.
(ii) Modification No. 8/0803, Service Bulletin No. 8-27-47, ‘Flight Controls - Flap Power Drive Unit - Replacement of Flow Regulator Valve’.
Part III. For aircraft serial numbers 3 through 293:
Modify the wing flap system torque sensor in accordance with Boeing Canada/de Havilland Service Bulletin No. 8-27-61.
Note: Transport Canada AD CF-89-09R4 refers.
Compliance: Part I:
- For aircraft serial numbers 3 through 177; within 300 hours time in service after 15 October 1992.
For aircraft serial numbers 178 through 231, 233, 235, 237 and 243; unless already accomplished, within 300 hours time in service after 13 October 1994.
2. Within 900 hours time in service after 15 October 1992. Part II:
- Within 300 hours time in service after 19 April 1990 (the compliance date of the previous issue of this Directive), and thereafter at intervals not to exceed 300 hours time in service.
2. Within 600 hours time in service after 19 April 1990 (the compliance date of the previous issue of this Directive), and thereafter at intervals not to exceed 1200 hours time in service.
Part III:
Within 2000 hours time in service or 9 months after 15 October 1992, whichever occurs first.
The compliance of the previous issue of this Directive remains unchanged except for the additional aircraft now included in Requirement Part I.
This Amendment is effective from 13 October 1994.
Background: There had been an incident of asymmetric flap where the caution light did not illuminate and the flap indicator remained at zero degrees. Investigation revealed that the primary drive shaft between the two port flaps and the splined coupling between the flap power unit and the starboard primary drive shaft had broken. Further, a secondary drive sensor failed to detect the shaft failure. A further investigation revealed that early serial number splined couplings received inadequate heat treatment. Amendment 1 required replacement of early couplings, a repetitive visual inspection of the flap systems, and an operational check of the torque sensor system.
Amendment 2 extended the serial number range of torque tubes having had inadequate design and heat treatment, required modification of the wing flap system torque sensor, and required terminating action for the on-going repetitive inspections. Amendment 3 corrected a serial number error in Table 1.
Amendment 4 is issued in response to a revision of the relevant Transport Canada AD which extends the serial number range of aircraft which require the inspections and possible replacement of splined torque tube couplings in accordance with Requirement Part I.