DHC-6 (Twin Otter) Series Aeroplanes
AD/DHC-6/62
Amdt 5
Applicability: All models.
Elevator Quadrant Control Column and Elevator/Rudder Pulley Brackets
9/96
Requirement: 1. Control Column.
- Inspect the control column, sub-assembly P/N C3CF39-17, for cracks or other damage.
b. Using a mirror and strong light, visually inspect the lower horizontal torque tube forming the base of the control column, paying particular attention to the welds and the region adjacent to the aileron chain exit holes. If cracks are discovered, the control column assembly must be either replaced by a serviceable unit or repaired within the time limits specified below.
(1) If the crack length is less than 25 mm, 150 hours of further flight is permissible before replacement or repair, provided that subsequent inspections are conducted at intervals not to exceed 25 flight hours and such inspections indicate that the crack length has not exceeded 25mm;
(2) For cracks greater than 25 mm but less than 50 mm in length, only a single flight to repair base is permissible before replacement or repair;
(3) For cracks greater than 50 mm in length, replace or repair prior to further flight. A serviceable unit may be one of the following:
(i) a complete new control column (P/N C6CF1225-51);
(ii) the existing column with a new lower welded assembly (P/N C3CF39- 17) installed;
(iii) the existing cracked component repaired in accordance with a scheme approved by the Authority. An acceptable scheme is specified in de Havilland Service Bulletin No. 6/180, Revision B (AD/DHC-6/17 Amdt 1 refers).
2. Elevator/Rudder Pulley Brackets.
Inspect pulley brackets P/N C6FS1263-27 and C6FS1263-29 and perform any corrective action in accordance with DHC SB A6/181.
3. Elevator Quadrant and Support Bracket.
Visually inspect the elevator quadrant for indications of distortion. The elevator quadrant on individual aircraft may be identified as P/N C6CFM1138-27 or C6CFM1450-27 or C6CFM1450-29 and is referred to as assembly P/N C6CF1137-1 or -3 or -5 or -7 in de Havilland Illustrated Parts Catalogue 27-30-00 figure 1, page 0, dated June 13, 1981.
COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Visually inspect the elevator quadrant for distortion by viewing the quadrant from the forward or aft direction to observe any warping or buckling, and by looking for the existence of score marks on the quadrant topside face due to its constant rubbing against the side of the cable guard. If the quadrant is found distorted, before further flight, replace it with a serviceable part and inspect the quadrant support bracket P/N C6CFM1142-1 for cracks using dye penetrant method. If the quadrant support bracket is found cracked, replace it with a serviceable part.
4 (a) Incorporate Modification 6/1433.
(b) Incorporate Modification 6/1262.
The above actions terminate the inspections of Requirements 1 and 2 respectively.
Note 1: Canadian AD CF-72-06 R3 refers.
Note 2: This Directive does not replace any inspection required by AD/DHC6/43 on applicable aircraft.
Compliance: Unless already accomplished:
Requirement 1. Before further flight after 21 February 1990 and thereafter at intervals not exceeding 100 hours time in service, and before further flight if the aircraft has been left standing in winds with a mean velocity estimated at 56 km/hr (30 knots) or greater; until modified in accordance with Requirement 4.(a).
Requirement 2. Before further flight after 21 February 1990 and thereafter daily, and before further flight if the aircraft has been left standing in winds with a mean velocity estimated at 56 km/hr (35 knots) or greater; until modified in accordance with Requirement 4.(b).
Requirement 3. Before further flight after 21 February 1990 and thereafter at intervals not exceeding 400 hours time in service.
Requirement 4. (a) Prior to 30 June 1993.
(b) Prior to 30 June 1992.
The compliance of the previous issue of this Directive remains unchanged, except Requirements 1 and 2 incorporate Compliance B from the previous issue.
This Amendment is effective from 15 August 1996.
Background: There was a case reported overseas of loss of elevator control shortly after take-off. The investigation revealed that the aircraft had been subjected to strong wind gusts that may have contributed to the failure of the elevator quadrant support bracket.
Amendment 1 made provision for the remote operations of this aircraft. Amendment 2 expanded the scope of the requirement to include the control column and the elevator/rudder pulley brackets. Amendment 3 made mandatory incorporation of the relieving modifications. Amendment 4 allowed additional time for the incorporation of modification 6/1433 due to unavailability of parts from de Havilland. Requirement 1 inspections were required until Modification 6/1433 was incorporated.
Amendment 5 is issued to align the requirement to inspect if the aircraft is left standing in strong winds, with the intent of the related Transport Canada AD. This inspection now only applies to Requirements 1 and 2.
The original issue of this Airworthiness Directive became effective on 2 January 1990.
Amendment 3 of this Airworthiness Directive became effective on 6 September 1990. Amendment 4 of this Airworthiness Directive became effective on 15 October 1992.