General rule is all controls neutral and collective fully down
Pretty hard to get it to beat itself to death under those conditions. Maybe a little pitch pulled.??
I do remember the TH-55 was notorius for this problem.....Same Aircraft just a little later in history.......
What do you think Sasless?
Just talked with a Pilot/Mech who has done work on them. He said flat pitch etc. wont matter if the Oleo Struts are not perfect. The thing eats itself rather quickly. Glad I started off in OH-23s.