About 1 mile from the platform, as the pilot was maneuvering in an attempt to reduce the airspeed, the helicopter began an inadvertent descent and then entered an aerodynamic buffet that hindered the pilot’s ability to maintain straight and level flight. The buffet was most likely caused by the helicopter entering transverse flow effect (unequal lift vectors between the front and rear portions of the rotor disc) and by a reduction in lift vectors, which resulted from the tailwind that was present. After encountering the buffet, the pilot was unable to maintain control of the helicopter or to stop the helicopter’s descent before it impacted the water.
Hm. Not sure I like summarizing transverse flow effect in this manner. We're talking about a longitudinal change in the flow pattern, coupled with a 90 degree delay in response. Causing a rolling motion similar to a cross wind. Agreed? We all deal with it on every take-off, and don't even think about it. Now, when we're slowing down, the reverse. Okay, got that.
Must admit though I never would have thought of that aspect of this accident pilot slowing down into that airspeed area leading to buffeting. Buffeting makes me think of "settling with power". But perhaps it is a combination of more than just settling with power. So slowing down into a state of transverse flow, the opposite of take-off, also contributed to the buffeting this poor pilot experienced?
Rightly or wrongly, I see transverse flow as a gradual, smooth phenomenon. I don't think I'd put buffeting on top of the list of observable symptoms.
Dammit, I do all this stuff and I've quit thinking about it. My brain hurts already.
