Does a helicopter have a button you can push like on a toy drone (and I am not even kidding) where you hit it and it will stop and hover in place?
Yes. A stable descent to a hover and landing can be automated, too. A 1991 S-76B does not have any of that.
I know virtually nothing about rotary wing, if a pilot yanks and banks, and pulls too hard, do copters stall like a fixed wing?
No, but you can experience "mushing" and if your speed is slow and you have 20-100% power applied, you can get into "Settling with Power." Either way, you will experience an uncommanded descent, possibly unrecoverable.
I thought that the key USP of helicopters is that that they can stay up without moving forward!?
Why not 'stop' or at least go very slow and figure things out? Can a helicopter autopilot hover?
Would it be an option to vertically decent over an open area?
Depending on the weight of the aircraft and the power available, it may not be possible to fly without forward speed to keep clean air into the rotor system.
Slowing down and going very slow is how you safely operate in reduced LEGAL weather (less that one SM visibility in SVFR and clear of clouds in class G) and that is what should have been happening if inflight visibility was deteriorating. The high speed recorded by radar is cause for questioning what was going wrong in the cockpit.
Yes, a helicopter autopilot can transition from forward flight to a hover and then descend vertically. Again, a 1991 S-76B does not have that capability.
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Operating a helicopter in reduced visibility and SVFR can be done safely and can save lots of time and airspace congestion, especially when there is no instrument procedure at or near the destination. Yes, you can always slow down, pick a spot and land if conditions get worse than forecast.
Helicopters are not like airplanes when it comes to low and slow, crappy weather operations. That's why almost all night operations done by aeromedical helicopters is done under NVGs. How many airplane-only pilots have ever even considered night ops with night vision systems?
Anyone can fly a helicopter, but the level of skill, proficiency and ADM needed to safely operate in really bad conditions requires much more training, experience and expensive hardware than most pilots realize. Despite all this, we still screw up and do dumb stuff every now and then.
I can't imagine going 145 KIAS in those conditions. Something went terribly wrong with either the pilot or the aircraft.
That's my $.02, anyway... R.I.P.