Airworthiness Directive · Amendment 39-22825 · Rotorcraft tail boom
Bell Textron Inc. Helicopters
This AD applies to the Bell Textron Inc. helicopters, certificated in any category, that are identified in paragraphs (c)(1) through (5) of this AD.
(1) Model 212 helicopters, serial numbers (S/N) 30501 through 30603 inclusive, 30611 through 30753 inclusive, 30755 through 30889 inclusive, 30891 through 30999 inclusive, 31101 through 31162 inclusive, 31164 through 31311 inclusive, 32101 through 32142 inclusive, and 35001 through 35103 inclusive;
(2) Model 412CF helicopters, S/N 46400 through 46499 inclusive;
(3) Model 412 and 412EP helicopters, S/N 33001 to 33078 inclusive, 33080 through 33129 inclusive, 33131 through 33138 inclusive, 33150 through 33213 inclusive, 36001 through 36687 inclusive, 36689 through 36999 inclusive, 37002 through 37018 inclusive, 37021 through 37051 inclusive, 38001, and 39101 through 39103 inclusive;
(4) Model 412EP helicopter, S/N 37052; and
(5) Model 412 and 412EP helicopters, S/N 36688, 37019, 37020, 37053 through 37999 inclusive, 38002 through 38999 inclusive, and 39104 through 39999 inclusive.
The FAA is adopting a new airworthiness directive (AD) for certain Bell Textron Inc. Model 212, 412, 412CF, and 412EP helicopters. This AD was prompted by reports of cracked tail boom attachment barrel nuts (barrel nuts). This AD requires replacing all steel alloy barrel nuts with nickel alloy barrel nuts, replacing or inspecting other tail boom attachment point hardware, repetitively inspecting torque, and repetitively replacing tail boom attachment bolts (bolts). This AD also prohibits installing steel alloy barrel nuts. The FAA is issuing this AD to address the unsafe condition on these products.
(1) Within 300 hours time-in-service (TIS) or 90 days after the effective date of this AD, whichever occurs first, accomplish the actions required by paragraphs (g)(1)(i) through (iv) of this AD, as applicable. For purposes of this AD, the word “new” is defined as having zero total hours TIS.
(i) For all helicopters identified in paragraphs (c)(1) and (2) of this AD; and for helicopters identified in paragraph (c)(3) of this AD that have accumulated 5,000 or more total hours TIS or 5 or more years since new, or if the total hours TIS or age of the helicopter is unknown, remove the upper left-hand (LH) steel alloy barrel nut part number (P/N) NAS577B9A and upper LH bolt from service and replace them with a new nickel alloy barrel nut P/N NAS577C9A, new retainer P/N NAS578C9A, and a new bolt in accordance with the Accomplishment Instructions, part I, paragraphs 4 through 7, of Bell Alert Service Bulletin 212-21-166, Revision A, dated February 23, 2022 (ASB 212-21-166 Rev A), Bell Alert Service Bulletin 412CF-21-72, Revision A, dated February 23, 2022 (ASB 412CF-21-72 Rev A), or Bell Alert Service Bulletin 412-21-187, Revision A, dated February 23, 2022 (ASB 412-21-187 Rev A), as applicable to your helicopter model, except you are not required to discard parts.
(ii) For helicopters identified in paragraph (c)(3) of this AD that have accumulated less than 5,000 total hours TIS and less than 5 years since new, remove the upper LH steel alloy barrel nut P/N NAS577B9A, the upper LH bolt, countersunk washer, and plain washers, and visually inspect the removed upper LH steel alloy barrel nut for cracking. If there is any cracking in the upper LH steel alloy barrel nut, before further flight, remove the upper LH bolt from service. If the upper LH bolt was not removed from service as a result of the upper LH steel alloy barrel nut inspection, visually inspect the upper LH bolt for any corrosion, damaged threads, wear, and fatigue cracking. If the upper LH bolt has any corrosion, a damaged thread, wear, or fatigue cracking, before further flight, remove the upper LH bolt from service. Regardless of the result of the upper LH steel alloy barrel nut inspection, remove the upper LH steel alloy barrel nut from service and replace it with a new nickel alloy barrel nut P/N NAS577C9A and new retainer P/N NAS578C9A. Install a new upper LH bolt or reinstall the existing upper LH bolt, as applicable, by following the Accomplishment Instructions, part I, paragraphs 6 and 7, of ASB 412-21-187 Rev A.
(iii) For helicopters identified in paragraphs (c)(1) through (3) of this AD, remove the upper right-hand (RH) steel alloy barrel nut P/N NAS577B8A, the upper RH bolt, countersunk washer, and plain washers, and visually inspect the removed upper RH steel alloy barrel nut for cracking. If there is any cracking in the upper RH steel alloy barrel nut, before further flight, remove the upper RH bolt from service. If the upper RH bolt was not removed from service as a result of the upper RH steel alloy barrel nut inspection, visually inspect the upper RH bolt for any corrosion, damaged threads, wear, and fatigue cracking. If the upper RH bolt has any corrosion, a damaged thread, wear, or fatigue cracking, before further flight, remove the upper RH bolt from service. Regardless of the result of the upper RH steel alloy barrel nut inspection, remove the upper RH steel alloy barrel nut from service and replace it with a new nickel alloy barrel nut P/N NAS577C8A and new retainer P/N NAS578C8A. Install a new upper RH bolt or reinstall the existing upper RH bolt, as applicable, by following the Accomplishment Instructions, part I, paragraphs 11 and 12, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model.
(iv) For helicopters identified in paragraphs (c)(1) through (3) of this AD, remove one of the lower steel alloy barrel nuts P/N NAS577B6A, its lower bolt, countersunk washer, and plain washers, and visually inspect the removed lower steel alloy barrel nut for cracking. If there is any cracking in the lower steel alloy barrel nut, before further flight, remove the lower bolt from service. If the lower bolt was not removed from service as a result of the lower steel alloy barrel nut inspection, visually inspect the lower bolt for any corrosion, damaged threads, wear, and fatigue cracking. If the lower bolt has any corrosion, a damaged thread, wear, or fatigue cracking, before further flight, remove the lower bolt from service. Regardless of the result of the lower steel alloy barrel nut inspection, remove the lower steel alloy barrel nut from service and replace it with a new nickel alloy barrel nut P/N NAS577C6A and new retainer P/N NAS578C6A. Install a new lower bolt or reinstall the existing lower bolt, as applicable, by following the Accomplishment Instructions, part I, paragraphs 16 and 17, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model. Repeat the actions required by this paragraph for the other lower tail boom attachment point.
(2) For helicopters identified in paragraphs (c)(1) through (3) of this AD, after accumulating 1 hour TIS, but not to exceed 5 hours TIS after accomplishing the actions required by paragraph (g)(1) of this AD, using the torque value information in the Accomplishment Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model, inspect the torque applied on each bolt. Thereafter, repeat the torque inspection of each bolt after accumulating 1 hour TIS, but not to exceed 5 hours TIS, to determine if the torque has stabilized. Do not exceed three torque inspections total for each bolt and accomplish the actions required by paragraphs (g)(2)(i) and (ii) of this AD.
Note 1 to the introductory text of paragraph (g)(2): This note applies to the introductory text of paragraph (g)(2), the introductory text of paragraph (g)(2)(i), paragraph (g)(2)(i)(B), and paragraph (g)(2)(ii) of this AD. The Accomplishment Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, and ASB 412CF-21-72 Rev A each refer to part I for allowable torque limits; part I of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, and ASB 412CF-21-72 Rev A specify the different torque limits for the different bolts.
(i) If the torque on a bolt is below the minimum allowable torque limit as a result of any instance of the torque inspection or if after three torque inspection attempts, the torque on any bolt has not stabilized, before further flight, accomplish the actions required by paragraphs (g)(2)(i)(A) and (B) of this AD.
(A) Remove the hardware set of one failed tail boom attachment point (barrel nut, retainer, bolt, countersunk washer, and plain washers). Remove the barrel nut and retainer from service as applicable to the affected tail boom attachment point. Visually inspect the removed bolt for any corrosion, damaged threads, wear, and fatigue cracking. If the bolt has any corrosion, a damaged thread, wear, or fatigue cracking, before further flight, remove the bolt from service.
(B) Install a new bolt or reinstall the existing bolt, as applicable, and a new nickel alloy barrel nut P/N NAS577C9A, NAS577C8A, or NAS577C6A, and new retainer P/N NAS578C9A, NAS578C8A, or NAS578C6A, with the P/N of the new nickel alloy barrel nut and the P/N of the new retainer being as applicable to the affected tail boom attachment point by following the Accomplishment Instructions, part I, paragraphs 6 and 7, paragraphs 11 and 12, or paragraphs 16 and 17, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model and with the paragraphs as applicable to that bolt. Repeat the actions required by paragraphs (g)(2)(i)(A) and (B) of this AD for each failed tail boom attachment point, one hardware set at a time. Then repeat the actions required by paragraph (g)(2) of this AD just for each newly installed or reinstalled bolt until the torque for all four tail boom attachment points stabilizes.
(ii) If the torque for all four tail boom attachment points has stabilized, before further flight, apply a torque stripe to all four bolts.
(3) For the helicopter identified in paragraph (c)(4) of this AD, within 5 hours TIS after the effective date of this AD, inspect the torque applied on each bolt in accordance with the Accomplishment Instructions, part II, paragraphs 1 and 2, of ASB 412-21-187 Rev A. Thereafter, repeat the torque inspection of each bolt after accumulating 1 hour TIS, but not to exceed 5 hours TIS, to determine if the torque has stabilized. Do not exceed three torque inspections total for each bolt and accomplish the actions required by paragraphs (g)(2)(i) and (ii) of this AD.
Note 2 to paragraph (g)(3): The Accomplishment Instructions, part II, paragraph 1, of ASB 412-21-187 Rev A refers to part I for allowable torque limits; part I of ASB 412-21-187 Rev A specifies the different torque limits for the different bolts.
(4) For helicopters identified in paragraphs (c)(1) through (4) of this AD, within 600 hours TIS or 12 months, whichever occurs first after applying torque stripes to all four bolts as required by paragraph (g)(2)(ii) of this AD, and thereafter within intervals not to exceed 600 hours TIS or 12 months, whichever occurs first; and for helicopters identified in paragraph (c)(5) of this AD, within 600 hours TIS or 12 months after the effective date of this AD, whichever occurs first, and thereafter within intervals not to exceed 600 hours TIS or 12 months, whichever occurs first, using the torque value information in the Accomplishment Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model, inspect the torque applied on each bolt. If the torque on any bolt is below the minimum allowable torque limit, accomplish the actions required by paragraphs (g)(4)(i) and (ii) of this AD.
(i) Before further flight, remove the hardware set of one failed tail boom attachment point (barrel nut, retainer, bolt, countersunk washer, and plain washers). Visually inspect the removed barrel nut for cracking, corrosion, and loss of tare torque. If the barrel nut has any cracking, corrosion, or has lost any tare toque, before further flight, remove the barrel nut and retainer from service and replace them with a new nickel alloy barrel nut P/N NAS577C9A, NAS577C8A, or NAS577C6A, and new retainer P/N NAS578C9A, NAS578C8A, or NAS578C6A, with the P/N of the new nickel alloy barrel nut and the P/N of the new retainer being as applicable to the affected tail boom attachment point. Regardless of the result of the barrel nut inspection, remove the bolt from service and replace it with a new bolt by following the Accomplishment Instructions, part I, paragraphs 6 and 7, paragraphs 11 and 12, or paragraphs 16 and 17, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model and with the paragraphs as applicable to that bolt. Repeat the actions required by this paragraph for each failed tail boom attachment point, one hardware set at a time.
(ii) After accumulating 1 hour TIS, but not to exceed 5 hours TIS after accomplishing the actions required by paragraph (g)(4)(i) of this AD, using the torque value information in the Accomplishment Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model, inspect the torque applied on each newly installed bolt. Thereafter, repeat the torque inspection of those bolts after accumulating 1 hour TIS, but not to exceed 5 hours TIS, to determine if the torque has stabilized. Do not exceed three torque inspections total for those bolts and accomplish the actions required by paragraphs (g)(2)(i) and (ii) of this AD.
Note 3 to paragraph (g)(4): The Accomplishment Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, and ASB 412CF-21-72 Rev A, each refer to part I for allowable torque limits; part I of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, and ASB 412CF-21-72 Rev A, specify the different torque limits for the different bolts.
(5) Within the compliance times specified in Table 1 to the introductory text of paragraph (g)(5) of this AD, accomplish the actions required by paragraphs (g)(5)(i) through (iv) of this AD.
(i) Remove the upper LH bolt from service and replace it with a new upper LH bolt by following the Accomplishment Instructions, part I, paragraphs 6 and 7, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model. Then accomplish the actions required by paragraph (g)(5)(v) of this AD.
Note 4 to paragraph (g)(5)(i): This note applies to paragraphs (g)(5)(i) through (v) of this AD. The Accomplishment Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, and ASB 412CF-21-72 Rev A, each refer to part I for allowable torque limits; part I of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, and ASB 412CF-21-72 Rev A, specify the different torque limits for the different bolts.
(ii) With the upper RH bolt removed, visually inspect the upper RH bolt for any corrosion, damaged threads, wear, and fatigue cracking. If the upper RH bolt has any corrosion, a damaged thread, wear, or fatigue cracking, before further flight, remove the upper RH bolt from service. Install a new upper RH bolt or reinstall the existing upper RH bolt, as applicable, by following the Accomplishment Instructions, paragraphs 11 and 12 of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model. Then accomplish the actions required by paragraph (g)(5)(v) of this AD.
(iii) With the lower LH bolt removed, visually inspect the lower LH bolt for any corrosion, damaged threads, wear, and fatigue cracking. If the lower LH bolt has any corrosion, a damaged thread, wear, or fatigue cracking, before further flight, remove the lower LH bolt from service. Install a new lower LH bolt or reinstall the existing lower LH bolt, as applicable, by following the Accomplishment Instructions, paragraphs 16 and 17 of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model. Then accomplish the actions required by paragraph (g)(5)(v) of this AD.
(iv) With the lower RH bolt removed, visually inspect the lower RH bolt for any corrosion, damaged threads, wear, and fatigue cracking. If the lower RH bolt has any corrosion, a damaged thread, wear, or fatigue cracking, before further flight, remove the lower RH bolt from service. Install a new lower RH bolt or reinstall the existing lower RH bolt, as applicable, by following the Accomplishment Instructions, paragraphs 16 and 17 of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model. Then accomplish the actions required by paragraph (g)(5)(v) of this AD.
(v) After accumulating 1 hour TIS, but not to exceed 5 hours TIS after accomplishing the actions required by paragraph (g)(5)(i), (ii), (iii), or (iv) of this AD, using the torque value information in the Accomplishment Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model, inspect the torque applied on each bolt. Thereafter, repeat the torque inspection of those bolts after accumulating 1 hour TIS, but not to exceed 5 hours TIS, to determine if the torque has stabilized. Do not exceed three torque inspections total for those bolts and accomplish the actions required by paragraphs (g)(2)(i) and (ii) of this AD.
(6) For helicopters identified in paragraph (c) of this AD, as of the effective date of this AD, do not install a steel alloy barrel nut P/N NAS577B9A, P/N NAS577B8A, or P/N NAS577B6A on any helicopter.
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.
