S76 Airworthiness Directive
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S76 Airworthiness Directive
Anyone here about this? What are the implications?
2010-17-16 Sikorsky Aircraft Corporation: Amendment 39-16408; Docket No. FAA-2008-0609; Directorate Identifier 2008-SW-24-AD.
Applicability: Model S-76A, S-76B, and S-76C helicopters, with serial numbers 76005 through 760578, inclusive, and serial number 762976, with any of the following part-numbered vertical stabilizer aft spar assemblies having 1,000 or more hours time-in-service (TIS) installed, certificated in any category.
Compliance: Required as indicated.
To detect and correct an unbalanced or out-of-track tail rotor, which could lead to increased vibrations, a fatigue crack, loss of a portion of the vertical stabilizer, and subsequent loss of control of the helicopter, accomplish the following: ...
2010-17-16 Sikorsky Aircraft Corporation: Amendment 39-16408; Docket No. FAA-2008-0609; Directorate Identifier 2008-SW-24-AD.
Applicability: Model S-76A, S-76B, and S-76C helicopters, with serial numbers 76005 through 760578, inclusive, and serial number 762976, with any of the following part-numbered vertical stabilizer aft spar assemblies having 1,000 or more hours time-in-service (TIS) installed, certificated in any category.
Compliance: Required as indicated.
To detect and correct an unbalanced or out-of-track tail rotor, which could lead to increased vibrations, a fatigue crack, loss of a portion of the vertical stabilizer, and subsequent loss of control of the helicopter, accomplish the following: ...
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Reading the AD it means if you fly a lot of hours you will be doing reptitive checks until the end of the year by which time you will have incorporated the modification kit that terminates the AD. So I guess the sooner you carry out the AD the better for the operator obviously depending on available workshop hours.
Looks like the vertical stabiliser is cracking earlier than was thought possible and is very intolerant of an out of balance tail rotor.
Looks like the vertical stabiliser is cracking earlier than was thought possible and is very intolerant of an out of balance tail rotor.
Join Date: Mar 2009
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Is this another area of the vertical stabilizer or is the repair and beefup previously incorporated in this area cracking now?. Having been involved in helicopter vibration for more years than I care to admit the tail rotor balance was easy to carry out and did not alter significantly when checked on a 50 or 100 hour routine basis . With the advent of the IHUMS we were able to look at the balance through all the phases of flight but more importantly, because an axially orientated accelerometer was fitted as well as the vertical or inplane accelerometer, we could see the levels in that plane not just the "inplane balance".
Looking across the fleet of S76A and then when modified to S76A+ there were varying vibration levels, some very high and this was thought to be a possible contributory factor to the vertical stabilizer problems. If a high axial level was observed then a check of the tail rotor rigging and a tail rotor track could be carried out.
On the S61 we did actually have a system where we could make adjustment to the pitch links, based on the axial vibration phase and amplitude, to reduce the axial vibration but due to the size of the adjustment it was difficult to keep the barrel in position while tightening the lock nuts. This sort of approach can perhaps highlight if one of the blades or paddles is trying to find it's own flight path.
I would be interested to hear if anyone else has used this approach to monitoring the tail rotor vibration.
Looking across the fleet of S76A and then when modified to S76A+ there were varying vibration levels, some very high and this was thought to be a possible contributory factor to the vertical stabilizer problems. If a high axial level was observed then a check of the tail rotor rigging and a tail rotor track could be carried out.
On the S61 we did actually have a system where we could make adjustment to the pitch links, based on the axial vibration phase and amplitude, to reduce the axial vibration but due to the size of the adjustment it was difficult to keep the barrel in position while tightening the lock nuts. This sort of approach can perhaps highlight if one of the blades or paddles is trying to find it's own flight path.
I would be interested to hear if anyone else has used this approach to monitoring the tail rotor vibration.
