75-27-07 PILATUS AIRCRAFT LTD. and FAIRCHILD HILLER: Amendment 39- 2479. Applies to Pilatus Model PC-6 airplanes (all variants), serial numbers 338 through 623, manufactured by Pilatus Aircraft Ltd. and serial numbers 2001 through 2067, manufactured by Fairchild Hiller.
Compliance is required as indicated.
To prevent a fatigue failure of the pilot and copilot rudder bar junction welded seam, accomplish the following:
(a) Within the next 10 hours' time in service after the effective date of this AD, unless already accomplished, visually inspect the junction fillet welds of the pilot and copilot rudder bars (P/Ns 6232.145, 6232.241, and 116.35.06.004) and determine whether the weld covers the full 360 degrees of the rudder bar tube circumference or only 250 degrees of the rudder bar tube circumference. If the weld is determined to be of the improved 360 degrees design, no further action is required by this AD.
(b) If the fillet weld is found to be of the non-continuous (250degrees) weld design, visually inspect the rudder bar junction weld for cracks by applying magnaflux or by the dye check method in accordance with paragraph 2.1 of Pilatus Aircraft Ltd. Service Bulletin No. 120, dated January 1973, or an FAA-approved equivalent.
(c) If no cracks are found during the inspection required by paragraph (b) of this AD, within the next 100 hours' time in service and thereafter at intervals not to exceed 100 hours' time in service, visually inspect the rudder bar junction weld for cracks using a 10 power magnifying glass in accordance with paragraph 2.2 of Pilatus Aircraft Ltd. Service Bulletin No. 120, dated January 1973, or an FAA-approved equivalent.
(d) If cracks are found during an inspection required by paragraphs (b) or (c) of this AD, either repair the rudder bar junction weld in accordance with paragraph 2.3 of Pilatus Aircraft Ltd. Service Bulletin no. 120, dated January 1973, or an FAA-approved equivalent, or replace the rudder bars with newrudder bars of the same part number but with improved 360 degrees weld design.
(e) Within the next 100 hours' time in service after accomplishing the repair described in paragraph (d) of this AD, or, if no cracks were found during the inspections required by paragraphs (b) or (c) of this AD, within the next 300 hours' time in service after complying with the inspection requirements of paragraph (b) of this AD, replace the rudder bars, P/N 6232.145, 6232.241, with new rudder bars of the same part number incorporating the continuous full 360 degree fillet weld around the rudder bar circumference.
This amendment becomes effective on January 21, 1976.