Airworthiness Directive · Amendment 39-17050 · Rotorcraft tailboom
Bell Helicopter Textron Canada Limited Helicopters
This AD applies to Model 427 helicopters, serial numbers 56001 through 56084, certificated in any category.
We are adopting a new airworthiness directive (AD) for Bell Helicopter Textron Canada Limited (BHTC) Model 427 helicopters which requires replacing certain tailboom attachment hardware and at certain intervals thereafter, determining the torque of that tailboom attachment hardware. This AD was prompted by a review of the tailboom attachment installation, which revealed that the torque value of the bolts specified in the BHTC Model 427 Maintenance Manual and applied during manufacturing was incorrect and exceeded the torque range recommended for the bolts. The actions are intended to prevent an over- torque of the tailboom attachment bolt (bolt), bolt failure, loss of the tailboom, and subsequent loss of control of the helicopter.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
(1) Within 150 hours time-in-service (TIS) or 90 days, whichever occurs first, replace the tailboom attachment hardware (attachment hardware) as follows:
(i) Remove the left upper bolt, washers, and nut.
(ii) Install a new bolt, part number (P/N) NAS627-27; washer, P/N 140-007-29S25E6; washer(s), P/N NAS1149G0732P; and new nut, P/N 42FLW-720 in accordance with paragraphs 5.a) through 5.d) of the Accomplishment Instructions in BHTC Alert Service Bulletin No. 427-10-31, dated March 1, 2010 (ASB).
(iii) Run the nut onto the threads of the mating bolt with a torque wrench and measure the existing tare torque. Any bolt and nut used must have a minimum tare torque value of 14 inch/lbs.
(iv) Torque the nut in accordance with paragraphs 5.f) and 5.g) of the ASB.
(v) Coat the bolt head, nut, and washers with appropriate corrosion preventive compound to seal the joint.
(vi) At each remaining attachment location, remove the bolt, washers, and nut, and install the attachment hardware in accordance with paragraphs (e)(1)(ii) through (e)(1)(v) of this AD.
(2) After installation of the new attachment hardware, at intervals of not less than 1 hour TIS but not exceeding 5 hours TIS, determine the torque of each nut until the torque stabilizes at each attachment location. Thereafter, at intervals not to exceed 300 hours TIS, determine the torque of each nut. When determining the torque, it is acceptable to use the minimum tare torque of 14 inch/lbs (1.58 Nm) added to the minimum torque range of 550-560 inch/lbs (62.1 to 63.3 Nm). If you remove corrosion preventative compound during the torquing, recoat the bolt head, nut, and washers with appropriate corrosion preventive compound to seal the joint.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
