AD 99-25-12

This amendment supersedes an existing airworthiness directive (AD), applicable to Bell Helicopter Textron (Bell)-manufactured Model HH-1K, TH-1F, TH-1L, UH-1A, UH-1B, UH-1E, UH-1F, UH-1H, UH-1L, and UH-1P helicopters; and Southwest Florida Aviation SW204, SW204HP, SW205, and SW205A-1 helicopters, that currently requires modification and inspections of the tailboom vertical fin spar (vertical fin spar). This amendment requires the same modification and inspections plus two additional inspections and replacement of the vertical fin spar. This amendment is prompted by 6 accidents, 2 of which involved fatalities, involving fatigue cracks in the vertical fin spar that have occurred since the issuance of AD 97-20-09. The actions specified by this AD are intended to prevent in-flight failure of the vertical fin spar and subsequent loss of control of the helicopter.

Final rule

99-25-12 CALIFORNIA DEPARTMENT OF FORESTRY; FIREFLY AVIATION HELICOPTER SERVICES (PREVIOUSLY ERICKSON AIR CRANE CO.); GARLICK HELICOPTERS, INC.; HAWKINS AND POWERS AVIATION, INC.; INTERNATIONAL HELICOPTERS, INC.; TAMARACK HELICOPTERS (PREVIOUSLY RANGER HELICOPTER SERVICES, INC.); ROBINSON AIRCRANE; WILLIAMS HELICOPTER CORPORATION (PREVIOUSLY SCOTT PAPER CO.); SMITH HELICOPTERS; SOUTHERN HELICOPTER INC.; SOUTHWEST FLORIDA AVIATION; UTAH STATE UNIVERSITY; WESTERN INTERNATIONAL AVIATION, INC.; UNC HELICOPTERS; AND U.S. HELICOPTER, INC.: Amendment 39-11455. Docket No. 99-SW-02-AD. Supersedes AD 97-20-09, Amendment 39-10521, Docket No. 97-SW-35-AD. \n\n\tApplicability: Model HH-1K (Type Certificate Data Sheet (TCDS) H5NM), TH-lF (TCDS H12NM, and R00008AT), TH-1L (TCDS H5NM, H7SO, and H4NM), UH-1A (TCDS H3SO), UH-1B (TCDS H1RM, H3NM, H13WE, H3SO, H5SO, and R00012AT), UH-1E (TCDS H5NM, H7SO, H8NM, and H4NM), UH-1F (TCDS H2NM, H7NE, H11SW, H12NM, and R00008AT), UH-1H (TCDS H13WE, H3SO, H15NM, and R00007DE), UH-lL (TCDS H5NM, H7SO, and H4NM), UH-1P (TCDS H12NM, and R00008AT), and SW204 (TCDS H6SO), SW204HP (TCDS H6SO), SW205 (TCDS H6SO), and SW205A-1 (TCDS H6SO) helicopters, with tailboom vertical fin spar (vertical fin spar), part number (P/N) 205-032-899-all dash numbers, 205-030-846-all dash numbers, or 205-032-851-all dash numbers, installed, certificated in any category. \n\n\tNOTE 1: This AD applies to each helicopter identified in the preceding applicability provision, regardless of whether it has been otherwise modified, altered, or repaired in the area subject to the requirements of this AD. For helicopters that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (h) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent failure of the tailboom vertical fin (fin) spar and subsequent loss of control of the helicopter, accomplish the following: \n\t\n\t(a) Within 8 hours time-in-service (TIS), modify the vertical fin spar as follows: \n\n\t\t(1) Remove the 42o gearbox cover and open the drive shaft cover on the fin spar assembly (see Figure 1). \n\n\t\t(2) Remove the first four rivets from the fin spar located at the bottom of the fin spar left-hand side at the tailboom and fin spar junction, and the first four rivets aft of the junction along the lower edge of the fin spar side-skin as shown (see Figure 2). \n\n\t\t(3) Trim the fin spar left-hand skin using extreme care to not damage the fin spar assembly (see Figure 3). \n\n\t\t(4) Deburr the rivet holes and trimmed skin edges. Remove all debris. In a ventilated work area, remove any surface contaminants with a cloth that has been dampened with aliphatic naphtha or an equivalent cleaning solvent. \n\n\t\t(5) Reattach the side-skin to the fin spar using MS 20470AD rivets. DO NOT install the bottom two rivets into the fin spar where the skin was trimmed. \n\n\t\t(6) Attach the fin spar side-skin lower edge using the rivets specified in Figure 3. \n\n\t\t(7) Refinish all reworked areas. \n\n\t(b) After modifying the fin spar assembly, inspect the fin spar for cracks before further flight and thereafter, at intervals not to exceed 8 hours TIS as follows: \n\n\t\t(1) Remove the lower aft tailboom inspection door, located at tailboom station 180 (see Figure 1). \n\n\t\t(2) Remove the 42o gearbox cover and open the drive shaft cover on the fin (see Figure 1). \n\n\t\t(3) In a ventilated work area, clean all surfaces to be inspected with a cloth dampened with aliphatic naphtha or an equivalent cleaning solvent.(4) Through the lower aft tailboom inspection door, using a bright light and an inspection mirror, inspect the fin spar assembly adjacent to the tailboom top skin on the forward side, paying special attention to the left-hand edge and the adjacent surfaces (see Figures 1 and 2). \n\n\t\t(5) Using a bright light and a 10x or higher magnifying glass, inspect the fin spar assembly adjacent to the tailboom top-skin on the in-board and out-board sides, the vertical edge, and the two open rivet holes. Using a bright light and a mirror, inspect the aft side of the fin spar in the same area. Special attention must be given to the left-hand edge of the fin spar and any adjacent surfaces between fin stations 66.31 and 71.31 (see Figure 2). \n\n\t\t(6) If any crack is discovered on the fin spar, replace the fin spar assembly with an airworthy fin spar assembly before further flight. \n\n\t(c) Within 50 hours TIS, and thereafter at intervals not to exceed 50 hours TIS, inspect the fin spar assembly as follows: \n\n\t\t(1) Remove the 42o gearbox cover and open the driveshaft cover on the fin spar assembly (see Figure 1). Remove the aft lower fin fairing and fin access panels that allow access to the aft side of the forward fin spar and the secondary spar (see Figure 1). \n\n\t\t(2) In a ventilated work area, clean all surfaces to be inspected with a cloth dampened with aliphatic naphtha or an equivalent cleaning solvent. Using a bright light, 10x or higher magnifying glass, and a borescope as required, inspect all of the fin ribs, fittings, skins, and secondary aft spar of the fin assembly (see Figures 4 and 5). Pay particular attention to the upper and lower fittings at tailboom station 227 for cracked or corroded fittings or sheared or loose rivets. \n\n\t\t(3) Gain access to the canted bulkhead aft of tailboom station 194.30 through the most aft lower access covers by removing the aft access covers or position light fairings as required. Visually inspect the canted bulkhead forward and aft sides through the lower tailboom inspection hole and position light access holes for cracks, corrosion, or loose or sheared rivets in all skins, fittings and bulkheads using a bright light, an inspection mirror, and a borescope as required (see Figures 4 and 5). Pay particular attention to the area in the upper forward corners of the aft skin directly around the fin spar assembly and the overlap area of the top skin beneath the 42o gearbox for cracks, which are only visible from the underside. \n\n\t\t(4) Any crack found in the fin spar assembly requires replacement with an airworthy part. Replacing the entire fin spar configuration with an airworthy fin spar configuration that has been demonstrated to the FAA to satisfy the structural fatigue requirements of repeated high-torque events and is approved by the Manager, FAA, Rotorcraft Standards Staff, will constitute a terminating action for the requirements of this AD. Any corrosion, loose or sheared rivets, or cracked skins or ribs found within the inspection areas must be repaired prior to further flight. \n (d) Within 50 hours TIS, modify the fin spar as follows: \n\n\t\t(1) Remove the 42o gearbox cover and open the driveshaft cover on the fin spar assembly (see Figure 1). \n\n\t\t(2) Remove the next 10 rivets from the fin spar located at the bottom of the fin spar left-hand side at the tailboom and fin spar junction (see Figures 6 and 7, whichever is applicable). \n\n\tCAUTION: Extreme care must be taken when drilling and removing rivets from the side of the fin spar to ensure the fin spar assembly is not damaged. \n\n\t\t(3) Trim the fin left-hand side skin using extreme care to not damage the fin spar assembly to expose the spar outboard edge (See Figure 6 or 7, whichever is applicable). \n\n\t\t(4) Deburr the rivet holes and trimmed side skin edges. Remove all debris. In a ventilated work area, remove any surface contaminates with a cloth that has been dampened with aliphatic naphtha oran equivalent cleaning solvent. \n\n\t\t(5) Fabricate cover plates in accordance with the notes and drawings of Figure 8 or 9, whichever is applicable. Ream prepare the holes in the fin spar and parts and install HI-LOK fasteners. NOTE 2: Bell Helicopter Medium Structural Repair Manual, BHT-MED-SRM-1, pages 3-36 through 3-38, pertains to this installation and reaming procedure. \n\n\t\t(6) Refinish all reworked areas, close driveshaft and replace 42o gearbox cover. \n\n\t(e) After modification of the fin spar assembly, before further flight and thereafter at intervals not to exceed 100 hours TIS, inspect the fin spar for cracks as follows: \n\n\t\t(1) Remove the 42o gearbox cover, open the driveshaft cover on the vertical fin spar assembly, and remove the spar cover plate and filler plate from the lower left-hand side of the fin assembly (see Figures 1 and 8 or 9, whichever is applicable). \n\n\tCAUTION: Extreme care must be taken when removing the cover plate and filler from the side of the fin spar to ensure that the spar assembly is not damaged. \n\n\t\t(2) In a ventilated work area, clean the surface to be inspected with a cloth dampened with aliphatic naphtha. \n\n\tCAUTION: Do not use chemical paint strippers. Use Scotch-Brite Grade-A VFN and methyl-ethyl ketone (MEK) or a suitable solvent to remove the paint and primer in the inspection area. \n\n\t\t(3) Perform a dye-penetrant inspection of the exposed area of the fin spar (see Figures 6 and 7). \n NOTE 3: ASTM E1416 or MIL-STD-6866, or the Bell Helicopter Standard Practices Manual, BHT-ALL-SPM, Chapter 6.2, pertains to this inspection. \n\n\t\t(4) If any crack is discovered on the fin spar, replace the fin spar assembly with an airworthy fin spar assembly before further flight. \n\n\t\t(5) After inspection, apply zinc chromate primer to the bare surfaces. When dry, re-install the cover plate and the filler using fasteners specified in Figure 8 or 9, whichever is applicable. \n\n\t\t(6) Install the 42o gearboxcover and the driveshaft cover. \n (f) Within 12 calendar months, remove the fin spar, P/N 205-030-846-all dash numbers, P/N 205-032-899-all dash numbers, or P/N 205-032-851-all dash numbers, whichever is applicable, and replace it with an airworthy fin spar configuration that has been demonstrated to the FAA to satisfy the structural fatigue requirements of repeated high torque events, and is approved by the Manager, FAA, Rotorcraft Standards Staff. \n\n\t(g) Replacing the fin spar, P/N's 205-032-899-all dash numbers, 205-030-846-all dash numbers, or 205-032-851-all dash numbers, with an airworthy fin spar that has been demonstrated to the FAA to satisfy the structural fatigue requirements of repeated high torque events and approved by the Manager, FAA, Rotorcraft Standards Staff, constitutes a terminating action for the requirements of this AD. \n\n\t(h) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be usedif approved by the Manager, FAA, Regulations Group, Rotorcraft Standards Staff. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, FAA, Regulations Group. \n\n\tNOTE 4: Information concerning the existence of approved fin spar configurations and alternative methods of compliance with this AD, if any, may be obtained from the Regulations Group. \n\n\t(i) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the helicopter to a location where the requirements of this AD can be accomplished. \n\n\t(j) This amendment becomes effective on January 11, 2000.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding AD 97-20-09, Amendment 39-10521 (63 FR 26439, May 13, 1998), Docket No. 97-SW-35-AD, which is applicable to Bell-manufactured Model HH-1K, TH-1F, TH-1L, UH-1A, UH-1B, UH-1E, UH-1F, UH-1H, UH-1L, and UH-1P helicopters; and Southwest Florida Aviation SW204, SW204HP, SW205, and SW205A-1 helicopters, was published in the Federal Register on April 16, 1999 (64 FR 18845). That action proposed to require the same modification and inspections of the vertical fin spar as required by AD 97-20-09 plus additional inspections and replacement of the vertical fin spar, part number (P/N) 205-030-846-all dash numbers. \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\n\tOne commenter states that the AD should be made applicable only to operators that are using the affected helicopters in logging operations. The commenter feels that the accidents that have occurred were due to the aircraft being involved in logging operations and states that the two accidents referred to in AD 97-20-09 were caused by operators not performing AD 97-20-09. The commenter also states that the AD is unnecessary and cost prohibitive to those operators who do not perform logging operations. The FAA does not concur; cracks have been found in the vertical fin spar on aircraft that have had no operational time performing heavy lift operations. The FAA believes that this service difficulty stems from the repeated demand for high power from the helicopter regardless of the type of operation. \n\n\tAnother commenter states that (1) vertical fin failures are due to a combination of improper operation of the aircraft and/or helicopter inspection procedures and 2) the FAA's economic analysis estimate is 25 to 40% too low. The FAA partially concurs. As stated previously, cracks in the vertical fin are not necessarily directly related to heavy lift operation but to repeated demand for high-power. The commenter acknowledges that its cost estimate is based on modifications performed on other aircraft; those modifications were more substantial than the modifications proposed by the NPRM. The FAA is aware that currently there is only one spar approved for specific type certificated restricted category helicopters that meets the repeated high torque event substantiation requirements of this AD; the cost for that spar was used in the economic analysis. There are other persons who have applied for and are working on certification of other spars. Therefore the FAA agrees that the cost of those spars may be higher than the cost of the spars used in its economic analysis. However, there remains no better information upon which the FAA can rely. Additionally, the commenter offered suggestions for an alternate method of compliance (AMOC) to the actions specified in the NPRM. The suggestions included: 1) allowing the installation of supplemental type certificate (STC) SR00267SE with 212-030-447-101 or -117 spar; 2) assigning a life limit to all vertical fin spars for Bell-manufactured medium helicopters and require the installation of an exceedance-monitoring device with an uninterrupted data history. The first suggestion from the commenter cannot be adopted at this time because the fatigue substantiation for the cited STC did not include the effects of repeated high torque events during certification. However, if this is accomplished, the FAA will consider this option. The second suggestion cannot be adopted for various reasons. The first is that the type certificate holders of approved fin spars have chosen not to impose life limits on their installations and, rather than imposing life limits, the FAA feels that the current installation of "laminated fin spars" should be removed from service due to the nature of the failure mode of this part and the current safety problems that are being experienced with this particular design. Also, the FAA knows of no certified monitoring systems being installed on restricted category aircraft that may be used for maintenance credits. \n\n\tAn additional commenter states that the use of the words "repeated heavy lift operations" attempts to place the blame for those spar failures on the logging industry. The commenter states that the cause of the fin spar failures was the repeated application of engine torque and the tail rotor reaction thereof, not what was in the helicopter or hanging from the external hook. The commenter states that it is improper to infer logging by using the term "heavy lift operation;" it should use the term "high torque events." The FAA concurs and has changed the wording in this AD to "repeated high torque events." \n\n\tAnother commenter states that Note 1 of the NPRM could be interpreted to impose undue/unnecessary burden on operators who haveincorporated a modified commercial vertical fin assembly. The commenter further states that the proposed AD should not apply to his particular vertical fin assembly, which has been issued an STC. The FAA does not concur; the particular STC has not been substantiated or shown to meet the requirements of "repeated high torque events." \n\n\tThe same commenter states that the requirement to meet repetitive heavy lift structural limitations has been imposed on specific flight profiles and it imposes undue burden on heavy lift operators who have already spent money installing an STC which includes a spar configuration that has not been shown to meet the proposed fatigue requirements. The FAA does not concur that fatigue substantiation to correct an unsafe condition is imposing an undue burden on a particular set of operators. The NPRM for this AD was followed by other AD's that were applicable to the commercial equivalent model helicopters. In fact, any applicant for an AMOC, STC, typecertificate, or other type of approval will be required to meet the same repeated high torque events requirements. \n\n\tAfter careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed except that the term "repeated heavy lift" will be replaced by "repeated high torque events." Also, two other nonsubstantive changes have been made to paragraph (h) and Note 4 of the AD. In paragraph (h), the NPRM incorrectly states that alternative methods of compliance (AMOC) or adjustments of the compliance time may be approved by the "Manager, Rotorcraft Standards Staff, Rotorcraft Directorate." This is incorrect and has been changed to state that the Manager, Regulations Group, Rotorcraft Directorate, is responsible for approving any AMOC or adjustment of the compliance time. Note 4 of the NPRM states that information concerning the existence of approved AMOC may be obtainedfrom the "Rotorcraft Standards Staff;" this is also incorrect and has been changed to state that information may be obtained from the "Regulations Group." The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\n\tThe FAA estimates that 75 helicopters of U.S. registry will be affected by this AD, that it will take approximately 4 work hours to accomplish the initial inspection, 8 work hours to accomplish the initial and recurring inspections, 180 work hours to replace the vertical fin spar, and that the average labor rate is $60 per work hour. Required parts will cost approximately $200 for the modification and $15,000 for the replacement. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $2,004,000 to conduct an initial inspection, modify the vertical fin spars and conduct recurring inspections, and replace the vertical fin spars on all helicopters in the U.S.fleet. \n\n\tThe regulations adopted herein will not have a substantial direct effect on the States, on the relationship between the national Government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132. \n\n\tFor the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the FAA, Office of the Regional Counsel, SouthwestRegion, 2601 Meacham Blvd., Room 663, Fort Worth, Texas 76137. \n\nList of Subjects in 14 CFR Part 39 \nAir transportation, Aircraft, Aviation safety, Safety. \n\nAdoption of the Amendment \n\tAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n 1. The authority citation for part 39 continues to read as follows: \n Authority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 - (Amended) \n 2. Section 39.13 is amended by removing Amendment 39-10521 (63 FR 26439, May 13, 1998), and by adding a new airworthiness directive (AD), Amendment 39-11455, to read as follows: