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Inconel Approved for VHA Abrasion Strips
VHA’s 206B/L main rotor blades were initially designed with two or three overlapping abrasion strips covering the the leading edge. The inboard and middle abrasion strips were made from roll-formed stainless steel; the outboard tip nickel abrasion strip is electroformed in-house at VHA.
These abrasion strips are non-structural components of the main rotor blade assembly and serve to protect the underlying composite material from impact and erosion damage. The abrasion strips are designed to remain installed and in service even after sustaining damage due to erosion, impact, or cracking as long as no underlying void or debond has occurred (in the case of an impact).
While the main rotor blades’ stainless steel abrasion strips are the same material from the same manufacturer as the abrasion strips on our UH-1 tail rotor blades, which have flown up to 2,500 hours with no cracking, some customers are reporting cracks on their VHA main rotor blades within the first 1,000 hours of flight. The interim solution for these customers is to apply a polyurethane tape across the cracks as specified in Customer Service Specification 501 (CSS-501).
Most of the cracking seemed to occur on one batch of the abrasion strips installed on 206L mains, and we thought it might have been an isolated issue. But then we started receiving reports on 206B mains, so we began looking for a tougher corrosion-resistant material for main rotor blade abrasion strips. We performed several tests with Inconel, a trademarked nickel-chromium alloy used in many aerospace applications, including abrasion strips for various heavy-lift helicopters. Based on these tests and other empirical data, we believe that use of the Inconel will solve the main rotor blade abrasion strip cracking issues.
The FAA approved the use of Inconel as a change to all three main rotor blade STCs (P/N 20631000-101, 20635000-501, and 20633000-101) in late June. Main rotor blades manufactured starting in July 2021 contain Inconel abrasion strips, which should solve future abrasion strip cracking issues. Note that on the 206L main rotor blade (P/N 20633000-101), the inboard abrasion strip has been removed from new production blades to match the 206B main rotor blades.
VHA is currently working with customers who have experienced abrasion strip cracking to replace these strips with Inconel under warranty.
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For 206L LongRanger operators flying P/N 20633000-101 serial numbers A007-A009 or A012-A104, we would like to remind you that these blades are subject to AD 2022-22-08, which requires recurring tap inspections every 400 flight hours or 2,400 engine starts, whichever comes first. You can learn more about the tap test requirements and procedure in our video . These blades are likely to develop a delamination in the area of the weight pocket on the lower surface of the blade. The AD further requires removing the blades from service if the delamination reaches 6 inches in length. However, extensive company testing indicates that all blades will likely achieve their full retirement life before that occurs. So long as the delamination is monitored and does not exceed the permitted length, the blades are entirely safe to fly with no adverse effects on aircraft behavior or performance. Operators are required to report their findings at every inspection interval to VHA for tracking using the form on the last page of Service Bulletin 33000-4 . Completed forms should be emailed to info@vanhornaviation.com . Providing this data helps to ensure all operators of these blades remain safe. All of the identified blades are likely to have delaminations, so if none are detected please contact us for assistance. In addition, this AD is considered an interim action and once sufficient data is gathered it may be updated to reduce the required frequency of inspection. Refer to AD 2022-22-08 and SB 33000-4 for further information.
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