"Sixty five knots at 100 feet on approach."
In 2004, when I was taught to fly helicopters at Bell Helicopter by Wayne Brown, Kevin Brandt, Gary Young and all the fine Bell instructor pilots, a normal approach was described as starting at 500 feet agl and 50 knots. You flew a constant glide path and constant deceleration, ultimately arriving at a slow walk to the low hover. There was no mention of avoiding the HV curve on approach. About a week after starting flight training there, I was soloed, and then sent around the Texas countryside in their Jet Rangers doing what you needed to do for your rotorcraft private pilot rating. Prior to being soloed, I had seen touchdown autorotations from takeoff, climb, cruise and approach.
After leaving Bell, I went straight to Canadian Helicopters for a mountain course. Again, never heard anything about avoiding the HV curve on approach, and in fact learned about a flat disk departure and loaded disk approach. It was drummed in to me that a stabilized approach had a loaded disk, and in that way there were no surprises as to power available at the bottom. On mountain approaches, recce passes were at 40, accelerating to 50 in the course reversal. You lived in the slow speed world, so you could observe ground speed and crab, and the disk better be loaded.
In the years since then, and many visits back to Bell, MD and Canadian Helicopters, I haven't heard anything different on avoiding the HV curve on approach. It generally is a question asked at recurrent, with the correct response being the HV curve does not apply on approach. As I reflected on 65 knots at 100 feet today, it just seemed inconsistent with a normal approach, a steep approach or a standard mountain approach.
In case, I was doing something different and not realizing it, I decided to go test it this afternoon. I was flying a 407 at loaded weight under 4,000 pounds here in Alaska. Since with the FADEC operating, it is almost impossible to get the Nr off 100 per cent, I could do almost any maneuver that I wanted on approach trying to stay out of the HV curve or be at 65 knots at 100 feet.
I flew on and off airport, making approaches to the taxiway, to confined areas and flat open meadows. Even with 5-20 knots of wind, I could not be at 65 KIAS at 100 feet, or stay completely out of the HV curve and be on any semblance of normal, steep or mountain approach. The best thing I can say about 65 KIAS at 100 feet is, it is a great profile for an autorotation.
As long as we are on the topic of "safest final approach," why is it that the "operators" are willing to land down wind with 10 or 15 knots on the tail, when an extra 20 seconds of flight could set them up for an into the wind approach. That got me thinking about the HV curve and wind, and I assumed that surely the HV curve was predicated upon no wind or a headwind. Went and dug out the HV curve for the 407 in the RFM, and there was no mention on the chart of wind. Thought surely it must be in the notes but couldn't find it. Called my buddy at Bell, and he explained to me that the HV curve is predicated upon a hard surface, where a helicopter could slide forever, and doesn't need to be zeroed out. My take away from this is while it isn't real bright to depart or land downwind over a runway, if there is an alternative, it is flat out stupid to depart or land downwind over a surface where you need to zero out your ground contact or topple the ship.