I think some of us are over-complicating the issue of understanding the difference between 3-axis and 4-axis modes. Whether the airspeed or descent angle is controlled by cyclic or collective input during an approach is not really important for most people, unless you are a pilot on the type or a technical nerd. What is important for most to understand is how the aircraft behaves using the different modes.
To compare with our fixed-wing colleagues:
If an airliner is flying an instrument approach using the autopilot to take care of the localizer and glide-angle and airspeed is controlled by the FP, then it is a "3-axis mode". Then in the fixed-wing the throttles must be manipulated by the FP, in a Super Puma it is the collective (power control).
If the auto-throttle is used on the same approach in our airliner, then it is similar to "4-axis", fully hands off.
To state that 3-axis approaches are inherently dangerous is over the top, there are thousands of airliners out there doing non-precision approaches every day with no A/T. Higher work-load? Yes, but with proper training, SOP's and good CRM the risk can be managed and controlled very well.
Last edited by Jimmy 16; 6th Sep 2013 at 12:58.