Ian W knows of what he speaks.
Any of you who think you can always multitask in a highly demanding environment have forgotten your early days of instrument training where it was easily possible to break down your scan.
We try to plan ahead to prevent overloads, but occasionally stuff can snowball.
There is no pilot alive who's scan cannot be broken by the right circumstances.
It is how you recover from this mess that separates the men from the boys.
Judging from how little actual stick time airline pilots seem to be getting, I am amazed that loss of control incidents are not more prevalent.
The term scan as I am using it refers to the multi-sensory process of acquiring information regarding your flight from all sources. It is very close in meaning to situational awareness.