AD 2021-11-19 Airworthiness Directives; Bell Textron Canada Limited (Type Certificate Previously Held by Bell Helicopter Textron Canada Limited) Helicopters

Models named: 505. Read the applicability below — it usually turns on serial or part numbers too.

This AD applies to Bell Textron Canada Limited (type certificate previously held by Bell Helicopter Textron Canada Limited) Model 505 helicopters, certificated in any category, with a truss assembly part number (P/N) SLS-030-056-015 with a serial number listed in Attachment A of Bell Alert Service Bulletin (ASB) 505-19-12, Revision A, dated July 11, 2019 (ASB 505-19-12 Rev A).

Comply with this AD within the compliance times specified, unless already done.

Within 100 hours time-in-service (TIS) after the effective date of this AD, access the transmission restraint assembly and: (1) Remove the safety pin at each lower nut location of the aft bolts securing the restraint to the truss assembly. Use solvent (C-304) to remove the corrosion preventive compound on each nut and washer located under the RH and LH truss assembly clevis lower lug. (2) Loosen the torque on each lower nut while holding the bolt with a wrench until the washer turns freely while sitting on top of the nut. (3) Measure and record the tare of each nut. For purposes of this AD, tare is the torque required to overcome the internal friction between a self-locking nut and bolt as the nut is being turned on the bolt, but before the nut contacts the washer. Add a torque value of 20 inch-lbs to the measured tare of each nut and torque each nut to this new total value. (4) Inspect for a gap around the circumference between the nut and the washer and between the washer and the truss assembly clevis lower lug mounting surface of the RH and LH sides as illustrated in Figure 1 of ASB 505-19-12 Rev A (2 sheets). If there is a gap, measure the gap. (i) If there is a gap that is less than 0.003 inch (0.076 mm), before further flight, install the hardware using the original torque value of 40 to 58 foot-pounds (55 to 78 Nm) plus tare. Do not exceed the limit specified in this paragraph plus tare. Install a cotter pin and apply corrosion preventive compound (C-101) and torque seal lacquer (C-049) between the nut, washer, and lower surface of the truss assembly clevis. (ii) If there is a gap that is 0.003 inch (0.076 mm) to 0.020 inch (0.508 mm) inclusive, before further flight, install the hardware with a decreased torque value limit of 20 to 60 inch-pounds (2.3 to 6.8 Nm) plus tare. Do not exceed the limit specified in this paragraph plus tare. Install a cotter pin. You may install an additional washer P/N NAS1149E0863P before torqueing and installing the cotter pin while not exceeding the maximum limit of 60 inch-lbs plus tare. Apply corrosion preventive compound (C-101) and torque seal lacquer (C-049) between the nut, washer, and lower surface of the truss assembly clevis. Update records for your helicopter to indicate the new torque limits on one or both sides. (A) Within 100 hours TIS after performing paragraph (g)(4)(ii) of this AD, and thereafter at intervals not to exceed 100 hours TIS, inspect the assembly for fretting between the washer and truss lower lug mounting surface, inspect the security of the pitch restraint attachment hardware to make sure it does not turn freely, and inspect the torque seal lacquer between the nut and the washer to make sure the torque seal is intact on the RH and LH sides. (B) If there is any fretting, the pitch restraint attachment hardware turns freely, or a torque seal is broken, remove the cotter pin from service and remove the nut, washer, and bolt. Inspect the bolt for damage and the lower surface of the truss assembly clevis lower lug for fretting damage. (1) If the bolt has damage, remove the bolt from service. (2) If the lower surface of the truss assembly clevis lower lug has fretting damage within allowable repair limits, use 400 grit sandpaper (C-423) and rework fretting damage smooth with adjacent surfaces, while removing minimum material. Do not exceed .010 inch (0.254 mm) deep total cumulative amount of material to be removed from the clevis's lower lugs compared to adjacent original surfaces after rework. Clean with acetone (C-316) and let dry. With the acetone dry, visually inspect the clevis lower lug for any cracks. (i) If there is a crack within allowable repair limits, repair in accordance with FAA-approved procedures. If there is a crack that meets or exceeds allowable repair limits, remove the truss assembly clevis lower lug from service. (ii) If there is not a crack, apply primer (C-204) to the reworked surface and let dry. With the primer dry, apply final paint (polyurethane topcoat color No. 16492) to the reworked surface. (3) If the lower surface of the truss assembly clevis lower lug has fretting damage that exceeds allowable repair limits, before further flight, remove the truss assembly clevis lower lug from service. (C) Install a nut, washer, and bolt with a decreased torque value limit of 20 to 60 inch-pounds (2.3 to 6.8 Nm) plus tare. Do not exceed the limit specified in this paragraph plus tare. Install a cotter pin. You may install an additional washer P/N NAS1149E0863P before torqueing and installing the cotter pin while not exceeding the maximum limit of 60 inch-lbs plus tare. Apply corrosion preventive compound (C-101) and torque seal lacquer (C-049) between the nut, washer, and lower surface of the truss assembly clevis. (iii) If there is a gap that is more than 0.020 inch (0.508 mm), before further flight, remove the nut, washer, and bolt from service and repair or replace the truss assembly clevis lower lug in accordance with FAA-approved procedures.

The FAA is issuing this AD to address a gap between the transmission restraint assembly aft attachment hardware lower washer and the right-hand (RH) and left-hand (LH) mating airframe truss assembly (truss assembly) clevis lower lug. The unsafe condition, if not addressed, could result in increased stress, cracking and failure of one or both of the clevis lower lugs, and subsequent loss of pylon pitch stiffness, excessive pylon pitch motions leading to unknown cyclic inputs to the main rotor, and loss of control of the helicopter.

None.