Originally Posted by MB
Correct, when viewed from the perspective of the software designer.
Thank you. I'm always pleased to know when I have said something that is right, especially when it is something on which I am expert
Also correct, BTW, when viewed from the perspective of the software user. In this case, the pilots.
Originally Posted by MB
But while the pilot has the luxury of throwing systems away (flying the plane manually)
You cannot fly most modern commercial transport aircraft "manually". Everything a pilot sees and does, from "raw data" to control responses, is part of a control system loop which goes through numbers of programmable-electronic systems. (I do acknowledge that on Boeing 737 aircraft, some of the control loops are still analogue mechanical systems. I doubt that will last another twenty years.) Anything a pilot wants to see or do rests on the reliable behavior of those programmable-electronic systems.
Maybe some just have to see it to believe it. We draw causal control-flow diagrams of airplane systems in which the pilot is part of the control loop. It is a valuable analytical technique which we occasionally try to teach to others, but for the most part remain best at ourselves. For most control parameters (or what one might think of as such), these graphs have twenty to forty elements, of which at most three are "pilot see", "pilot think", "pilot do" and the great proportion of the rest are programmable-electronic.
Now, all of those programmable-electronic elements are subject to the statistical phenomena about which I have been talking. If you think that an anomalous condition can most always be saved by those three nodes containing the word "pilot" above, then I can only admire your faith in the ability of software engineers to write perfect multi-ten-thousand-to-million-line programs. I can also say that few in the industry share that faith, although some do profess it publically on behalf of their employers.
PBL