AD 99-15-14

This amendment adopts a new airworthiness directive (AD), applicable to Sikorsky Aircraft-manufactured Model CH-54B helicopters, that requires initial and recurring inspections and rework or replacement, if necessary, of the second stage lower planetary plate (plate). This amendment is prompted by two reports of cracked plates that have been found during overhaul and inspections. The actions specified by this AD are intended to prevent failure of the main gearbox plate due to fatigue cracking, which could lead to failure of the main gearbox and subsequent loss of control of the helicopter.

Final rule

99-15-14 BLUE BIRD HELICOPTERS: Amendment 39-11235. Docket No. 97-SW-59-AD.\n\n\tApplicability: CH-54B helicopters with main gearbox second stage lower planetary plate (plate), part number (P/N) 6435-20516-101, 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 (c) 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 plate due to fatigue cracking, which could lead to failure of the main gearbox and subsequent loss of control of the helicopter, accomplish the following:\n\n\t(a)\tFor main gearbox assemblies containing plate, part number (P/N) 6435-20516-101, with 1,600 or more hours time-in-service (TIS):\n\n\tNOTE 2: If the TIS hours of the plate is not known, use the main gearbox assembly's total operating time.\n\n\t\t(1)\tPrior to the first flight of each day, inspect the main oil filter for magnesium contamination. If magnesium contamination is discovered, replace the main gearbox assembly.\n\n\t\t(2)\tWithin the next 100 hours TIS after the effective date of this AD, and thereafter at intervals not to exceed 200 hours TIS, conduct a borescope inspection of the plate for cracks in the area of the nine lightening holes (see Figure 1). If a crack is found, replace the plate with an airworthy plate. The plate, P/N 6435-20516-101, is part of the main gearbox second stage planetary set (P/N 6435-20514-041), which is a serialized matched set, and must be replaced as a set.\n\n\t(b)\tAt the next overhaul of the main gearbox assembly, inspect and rework the plate, P/N 6435-20516-101, as follows:\n\n\t\t(1)\tFluorescent magnetic particle inspect the plate per ASTM E1444 in circumferential and longitudinal directions using a wet continuous method. Pay particular attention to the area around the nine 1.750-inch diameter lightening holes.\n\n\t\t(2)\tIf a crack is found, the plate is unairworthy. Replace it with an airworthy plate.\n\n\t\t(3)\tIf no crack is found, rework the plate as follows, ensuring that all plate surfaces are free of any crack, scratch, dent, or corrosion.\n\n\t\t\t(i)\tMeasuring from the center of each 1.750-inch diameter lightening hole, machine 0.015/0.020 inch from the radius of the hole (see Figure 2). Machined surface roughness shall not exceed 63 microinches AA rating.\n\n\t\t\t(ii)\tApply a 0.030/0.050-inch radius on the top and bottom edge of each hole.\n\n\t\t(4)\tFluorescent magnetic particle inspect the reworked areas per ASTM E1444 in circumferential and longitudinal directions using a wet continuous method.\n\n\t\t(5)\tIf a crack is found, the plate is unairworthy. Replace it with an airworthy plate.\n\n\t\t(6)\tIf no crack is found, rework the plate as follows:\n\n\t\t\t(i)\tRemove the protective finish from the specified areas on the top and bottom of the plate as follows:\n\n\t\t\t\t(A)\tMask the top and bottom of the plate leaving exposed a 3.20-inch minimum circumferential band centered on 13.75-inch diameter of plate (see Figure 2). Mask the area to protect the thrust washer and the surrounding areas from vapor blast.\n\n\t\t\t\t(B)\tUsing a vapor blast machine, remove the protective finish from the exposed circumferential band on the top and bottom of the plate. Use No. 220 aluminum oxide grit at a pressure of 80 - 90 pounds per square inch.\n\n\t\t\t(ii)\tShotpeen the specified areas on the plate by remasking the top and bottom of the plate leaving exposed the 3.20-inch minimum circumferential band centered on 13.75-inch diameter of the plate. Mask the area to protect the thrust washer and the surrounding areas from the shot peening process.\n\n\t\t\t(iii)\tShot peen the inside diameter of the lightening holes and the upper and lower surfaces of the plate in the 3.20-inch minimum circumferential band to 0.008 to 0.012A intensity, ensuring 200% coverage per MIL-S-13165C or latest revision. Use cast steel shot, size 170. Use a tracer dye inspection method.\n\n\tNOTE 3: Overspray is permitted to allow a feathering application during the peening process from the peened surface to the non-peened surface.\n\n\t\t\t(iv)\tFinish the reworked surfaces as follows:\n\n\t\t\t\t(A)\tClean the surfaces thoroughly with acetone (Fed. Spec O-A-51, or equivalent).\n\n\t\t\t\t(B)\tApply Presto black or blueing touchup solution to the reworked surfaces with cotton swabs. The solution temperature must be between 21° C and 49° C (70° F to 120° F). Keep the surfaces wet for about three minutes to get a uniform dark color.\n\n\t\t\t\t(C)\tRinse the surface in cold running water and dry with forced air.\n\tNOTE 4: A hot water rinse may be used after the cold water rinse to speed up drying time.\n\n\t\t\t\t(D) Using steel wool, Grade 00 or finer, rub the surfaces lightly. Polish with a soft cloth and then coat with a preservative oil (MIL-C-15074).\n\n\t\t\t(v)\tIdentify the reworked plate by stamping the number of this AD after the part number. Use a low-stress depth-controlled impression-stamp with full fillet depth of no more than 0.003 inch (see Figure 2). Marking must be such that it cannot be construed as part of the part number.\n\n\t(c)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Rotorcraft Certification Office, FAA, Rotorcraft Directorate. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, Rotorcraft Certification Office.\n\n\tNOTE 5: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Rotorcraft Certification Office.\n\n\t(d)\tSpecial 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(e)\tThis amendment becomes effective on August 26, 1999.\n\nFigure 1: 99-15-14\n\n\n\nBorescope Inspection of Second Stage\nLower Planetary Plate Lightening Holes\nFigure 1\n\nFigure 2: 99-15-14\n\n\nRework of Second Stage Lower Planetary Plate\nFigure 2

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to Sikorsky Aircraft-manufactured Model CH-54B helicopters was published in the Federal Register on April 16, 1999 (64 FR 18835). That action proposed to require initial and recurring inspections, and rework or replacement, if necessary, of the plate.\n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. No comments were received on the proposal or the FAA's determination of the cost to the public. The FAA has determined that air safety and the public interest require the adoption of the rule as proposed.\n\n\tThe FAA estimates that 4 helicopters of U.S. registry will be affected by this AD, that it will take approximately 8 work hours per helicopter to accomplish the borescope inspection, 1 work hour to inspect the main gearbox oil filter pack, 140 work hours toremove and replace the main gearbox assembly, if necessary, and 20 work hours to rework the plate, and that the average labor rate is $60 per work hour. Required parts will cost approximately $8,000 per helicopter. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $67,760; $2,160 to accomplish the initial inspections and $65,600 to replace the plate in the main gearbox assembly in all 4 helicopters, if necessary. Daily preflight inspections of the main gearbox oil filter pack will cost $60 per helicopter for each day flight is conducted.\n\n\tThe regulations adopted herein will not have substantial direct effects 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, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.\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 Office of the Regional Counsel, Southwest Region, 2601 Meacham Blvd., Room 663, Fort Worth, Texas 76137.\n\nList of Subjects in 14 CFR Part 39\n\tAir 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:\nPART 39 - AIRWORTHINESS DIRECTIVES\n\t1. The authority citation for part 39 continues to read as follows:\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701.\n§ 39.13 (Amended)\n\t2. Section 39.13 is amended by adding a new airworthiness directive to read as follows: