Originally Posted by
Salusa
I believe that the description of "Collective Bounce" is a misnomor at best.
In the instances I was personally involved with, the pilots literally thought that their time was up and the aircraft was going to throw itself apart.
I'm not going to embellish the facts with how they described it to me "post incident" but suffice to say I was at first sceptical then that gave way to concern.
Both instances occurred before VHA provided any formal feedback.
Subsequently and after I don't know how after how many reports were made to VHA, advice was issued over time in three statements.
In order of issue:
1. Offset Cyclic to right,/do not lower collective.
2. Raise Collective and offset Cyclic.
3. Sweep both blades aft two points to reduce likelihood of onset.
Item 3 obviously being a maintenence action.
Yes, the situation when it occurs is controllable providing the pilot has been made aware of the phenomenon and is briefed on how to handle it.
Don't get me wrong VHA deliver a good product, just the information needs to made more readily available for operators and pilots.
Currently the distribution of that information is via Van Horn only and therefore relys on an organisations own internal procedures to pass that information onto the crews at the sharp end.
That may be the "weak point" right there?
Don't forget that up until last month, the only “official” info you could get on the issue was a blog post on VH’s website. A blog post. I think it had two or three short paragraphs.
I for one think that a lot of the basis of flight testing for the 206L blades may have been based on the 206B blades, on account of the sharing of the type certificate. Given the difference in transmission mounting systems and that VH said (in their blog post) that it was a harmonic interaction between the MRBs and the Nodal Beams, one can assume there was inadequate testing before release and up until now they’ve been doing what they can to minimize the issue to avoid a recall. Blaming Collective Bounce offloads the responsibility to a known boogeyman just as Bell did with LTE for decades.
Even if the VH blades didn’t cause this accident, or if they blame it on the operator due to improper sweep on the blades, or god forbid the pilot for not perusing the VH website enough to read their information letter, there is obviously an issue and it’s been kept pretty quiet up until now.