1.12 Development of a Fatigue safety performance model

influence on human performance, namely a higher frequency of errors committed by operating pilots” (Gander et al, 1996). Flight-crew have also displayed poor judgement when assessing intrinsic levels of alertness and fatigue (Dinges, 1995). Some individuals have stated that they were alert when in-fact they were in the process of falling asleep (Roth et al, 1994). There is also a trend to underestimate the level of one’s sleepiness (Rosekind and Schwartz, 1988, Ingre et al, 2006). A decrease in flight-crew alertness and performance reduces safety margins and this increases the risk of an incident or accident occurring being attributed to fatigue (Folkard, 2003). 
S. Stewart, F. Koornneef, R. Akselsson, and C. Turner  - HILAS 2009

The consequences and effects of fatigue on performance have been published and include (Summarised from Hawkins et al, 1983; Neri et al 1992; Caldwell et al, 1997; Dinges et al, 1995, Batelle Memorial Report, 1998; Rosekind et al, 1996 & Lawford, 2005):
. Degraded judgement and decision making of crew
. Deterioration in the accuracy and timing of actions, reduced reaction time
. A change in perception of risk and risk tolerance
. Crew involuntary lapses into sleep (microsleep events)
. Crew unconsciously accepting lower standards of performance

. A reduction in situational awareness (ability to integrate information into a system
model) . Crew performance becomes increasingly erratic and inconsistent . Crew attention range narrows and some tasks are forgotten or ignored; cognitive

fixation . An increased number of errors of omission, which increase to commission, when time pressure becomes a factor . An increase in both number and duration of lapses (forgetting) with increasing
fatigue
. Reduced visual perception
. A decline in CRM behaviours (effective communication and inter-personal

interactions; poor communication and coordination).
The relationship between fatigue causes and consequences has been captured diagrammatically in Figure 5.

S. Stewart, F. Koornneef, R. Akselsson, and C. Turner  - HILAS 2009

Sutton et al (2003) in their relational model (Figure 6) group the antecedents of fatigue under two main headings Job factors and Individual factors (Individual factors (trait and social) and Job Factors inclusive of Work factors (inclusive of environment, job design and workload) and Schedule related factors (time of day, shift system design, rest breaks).

The model includes and extends on the antecedents considered by ASLEF (2003) and Baker and Fergusson (2004) by showing diagrammatically inter-relationships between the causes and consequences of fatigue. Whilst these relational models show the causes and consequences of fatigue in an influence diagram, they fall short of establishing fatigue as a risk that must be managed through a safety management system. Also again, sleep deprivation is both a consequence and causal factor of fatigue that should be represented in such an influence diagram. Of note is that there is no arrow from Health to Human performance. That said, it is the first true model to effectively group the precursors and consequences of fatigue to performance (system and individual).
　
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