I've never felt comfortable with Prof Reason's "swiss cheese safety" description. It implies that environments such as aviation and medical care are naturally benign, with multiple protections in place, all functioning to optimum. Sounds nice on paper.
My experience of adverse incidents in both industries is that often "protections" are chronically suboptimal or below the reasonable level at which they can function as genuine "cheese", and many situations have at best only one layer of protection before disaster. Skilled operators see situations where protections are weak at an early stage in the evolution of the potential problem.
So.. if the papi is down, the ILS is down, you are forced to fly a difficult late approach profile, you may not practice hand flown landings with A/T disconnected, the PNF may not want to tell you "low and slow" and he/she are tired anyway, theres a bit of language problem and not much familiarity with the local environment, etc etc etc ... then there is not that much cheese around in the first place, just sub-threshold protections.
Last edited by Mimpe; 7th Jul 2013 at 11:39.