Collective control rigging

[cobrajock]

In the case of the 412 , that lost collective control because of collective lever severance , I have seen this many times in the past , and it has been attributed mostly to improper rigging of the collective flight control , which allows the collective levers to bottom out on top of the swash plate mounting bolts when the collective is in the full down position . This clearance is critical especially during the auto-rotative rpm check during the test flight , and after rigging has been accomplished . if this clearance is not there , and the levers bottom out on the mounting bolts , coupled with the 1500 psi hydraulic boost , the collective levers will be stressed to the point of fracture , and eventual complete severance , and failure .

[squib66]

I have seen this many times in the past


Care to add when, where, what type, what consequences?

[cobrajock]

First encounter with this was at Ft. Bragg NC , when I was a young MTP in the Attack Battalion flying AH-1G's , and one of our crew Cheifs was adjusting the lolipop bearing on the end of the collective control rod which attaches to the collective levers to adjust the auto rpm during a test flight . Although it worked for the first couple of adjustments , he eventually ran out of adjustment before the rpm could be within 310-315 , and the collective levers had "0" clearance between the top of the swash plate mounting bolts , and the levers themselves . What he should have been adjusting , was the P/C links in order to get the auto rpm in range . I was fortunate enough to have found this , and made the correction before any damage could be done . However over the next 35 years of flying UH-1C/M/H , and UH-1N/ST's all over the world , I have seen this same mistake several times ....