1510 W. Drake Drive, Tempe, Arizona USA 85283
206 Main Rotor Blade Trim Tabs
The Issue
Operators have reported partial debonding of trim tabs on a small number of main rotor blades.
Trim tab assemblies on VHA main rotor blades consist of two identical trim tabs that are bonded together and then bonded to the trailing edge of the main rotor blade structure. The trim tabs incorporate a joggle to allow the tab to fit over the trailing edge of the blade.
Early 206L MRB trim tabs had a shallow joggle that inadvertently allowed the trim tabs to be installed too far onto the blade assembly, thereby creating a preload in the bondline of the tab-to-blade bond regions. The preload created the potential for microcracking of the adhesive bondline when the trim tabs were adjusted.
Under extreme conditions, environmental contaminants were found to gradually penetrate the bondline and slowly cause delaminations of the trim tab assembly.
Note that this is not a safety of flight issue as trim tabs are used to adjust vibration levels caused by manufacturing variables to enhance ride comfort. The blades are shipped with trim tabs set neutral to the chord line, thus not affecting the rotor system, and many operators find that they don’t need to adjust the trim tabs during track and balance.
Repair Requirements
Any debonded trim tabs must be removed and rebonded to the trailing edge of the rotor blade. This can generally be done at the customer’s facility by personnel authorized in composite structures repair. Refer to VHA Service Bulletin
33000-3R2 for complete information and instructions.
VHA Solutions
- When operators contacted us about this issue, we immediately dispatched personnel from Van Horn Repair to repair the blades under warranty.
- We created new trim tab assembly kits to provide to operators.
- We redesigned the trim tabs to modify the joggle and eliminate the fit issue.
- We published Service Bulletin 33000-3R2 regarding this issue.
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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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