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Tiger AD - AD/DH82/15
DH82 /82A Tiger Moth – Information to Members Airworthiness Directive AD/DH82/15 – Aileron Control System For the information of members the following are the details of the modifications to the aileron control system required by the new AD. The compliance date is 31 March. Background Recently CASA discovered that they had not endorsed a very old mandatory AD from the UK CAA. As a result, airworthiness directive AD/DH82/15 was issued in October 2007 which adopts the UK CAA CAP 476 requirements outlined in Technical News Sheet (TNS) CT (Moth) No. 5. This results in some extensive mandatory modifications which apparently arose about 60 years ago in the The TNS and hence the Australian AD however only apply to aircraft of TNS No. 5 which describes the modifications, was extensively revised, including coloured illustrations, by De Havilland Support Limited in May 2007 and is now much easier to interpret. The following are the nine separate elements of the AD. 1. Aileron Sprocket Chain Guides (Mod. 125). This mod. prevents chain malfunction if cables become too slack. The following five (5) separate changes are made: 1.1 The original two bent metal chain guards are replaced with bolted-on spring guards (63085 & 63086). They look like two pieces of clock spring and impinge directly on the chain where it meets the sprocket. 1.2 Two spanwise guide plates (63092 & 63093) are introduced below the sprocket and are shimmed to give the appropriate clearance. 1.3 A chordwise guide plate (63081) is introduced to ensure a more suitable lead off from the sprocket. It is wood screwed to a strip of spruce packing. 1.4 The chain shackles H.11678, are replaced with a slimmer version (63084A). Unfortunately these items are not available and we are looking at a means of modifying the larger ones to suit. 1.5 Positive wooden stops are added below cockpit floor to limit stick lateral travel to 2.5” each side of centre line (total travel 5.0”) and prevent the cable end fittings contacting the sprocket at full stick travel. This modification is relatively easy to incorporate. It limits the aileron travel to eliminate any chance of the shackles attached to the chain from contacting the sprocket. 2. Seal Aileron Gear Box (Mod. 134). This modification is designed to prevent foreign objects from entering the area of the chain and sprockets and consists of: 2.1 An extension built into the original control box This mod. involves serious disturbance to the fabric and would be difficult to incorporate without removing the wing. The sole purpose of the extension appears to be to accommodate the fittings at the ends of the aileron cables. 2.2 A felt seal is introduced into an extended aileron control box. The extended box is fitted with a cover plate. 2.3 A spruce infill is installed in the channel above the aileron sprocket bracket. The purpose of this “dog bone” is to prevent foreign objects from lodging in the concave upper surface of the metal bracket. 3.0 Reinforcing Strips to Aileron box (Mod. 138). Both sides of the control box are reinforced with the addition of strips of plywood glued in place. Apparently this addresses a known problem, (known in the This has been made necessary because of splitting of the sides of the box because of the extra moment of the extended box of 2.1 above. AAAA Action The AAAA is putting together a case for deferring some of the more difficult modifications subject to incorporating certain others and introducing additional restrictions and or inspections. We will update the website as this progresses. Dick Gower Posted By Craig on:25-February-2008 8:34 am |