Originally Posted by Flight Safety
the design engineer [whom I referred to] is Jef Raskin
Jef Raskin was Apple's chief user interface designer and has a wonderful book on principles of interface design. For desktop computers. Yes, modes are awful in desktop computer SW, as anybody trying to do something less than trivial in Word or OpenOffice knows. We avoid them too, rigorously, in our WB-Graph-drawing SW.
Taking design principles for desktop-computer user interfaces and transferring them to critical systems with professional operators does not work.
Raskin was assuming untutored users on general-purpose computers with potentially unbounded functionality and varying degrees of creativity on the part of the users. Safety-critical control system interfaces assume professional users, a fixed number of well-defined and tested functions, and no creative use of the system. They are very different design spaces.
Since you apparently didn't understand the point I made earlier, I will repeat it. The reason modes are needed is that the flat state space is too large to expect an operator to negotiate it in real time. Please understand this: mode-less does not work.
You can show this to yourself. Go to my 1994 paper on the (pre-Warsaw) A320 braking logic. Compare the trivial factored state spaces (easy to understand) with their product (the flat state space). Look at the product for 15 minutes, and then attempt to draw it from memory on a clean sheet of paper. If you didn't get it quite right, you may rest assured that you are in the majority. And designing user interfaces for critical operations is all about ensuring that the professional operators get it right. So, no flat state spaces.
PBL