Originally Posted by
Spunk
...17 gusting 22 KTS... is considered to be significant turbulences?
Spunk, no not at all. This is the wind reported by a ground weather station in the area. This information was used to estimate the air speed vs the ground speed taken from the Sat tracker.
"Significant" turbulence is a term used by Robinson Helicopters, and it is operationally defined. It is not directly related to the terms mild/moderate/severe turbulence. Robinson says they deliberately avoid the reference to absolute measures of turbulence (those "moderate/severe" terms, which are not very well defined themselves) but refer to "significant" as in relation to the skills and experience of the pilot. They (rightly, in my opinion) say that what is easy to handle for an experienced pilot, may be significant to a low time pilot. (Sorry, I can't find my source for this right now.) And then they go on in saying that when encountering significant turbulence you should slow down to 60-70 KTS.
Robinson further restricts (however, only after this accident discussed here) VNE to 110KTS IAS "except in smooth air".
The notion of "significant turbulence" came in here via the report from another chopper pilot, which is included in the Factual Report:
... the pilot of an R44 who was performing aerial survey work (the day of the accident) immediately north of the accident site ... stated that beginning at 1130 the winds became stronger and gustier. Over the next couple of hours, he observed numerous dust devils, and experienced a significant updraft in excess of 1,000 ft per minute. About 1515 (local time), he decided to discontinue operations and encountered a significant wind shift while returning to his base.
That certainly was "significant" to the R44 pilot. The accident happened at 1425 local time.