Bio-mathematical models are useful to assess likely fatigue. They are normally a set of algorithms hosted within a software package that will predict a level of likely fatigue during or at the end of a duty.

Many scales of fatigue exist but the most common one is the Samn Perelli scale (see below) – a 7 level scale of alertness where level 1 is completely fresh and alertness is reduced for each increasing level until level 7 where the subject is completely exhausted.

Using a model can give a rapid indication of likely alertness on duty when assessing the resources required for a new route or network, timetable times, changes from summer to winter schedules or researching some emerging risk issues.

A model can also be helpful in researching likely fatigue in for during a Flight Operations Quality Assurance (FOQA) event or as a result of an incident or accident.

However, a model is never a comprehensive solution to be relied upon for complete accuracy. It is not a so-called  ‘silver  bullet’ as all models are based on the notional average person so further information will always be required to make a definitive judgement on matters of safety. This judgement is the evident bailiwick of the manager as that is precisely the reason for management -to assess risk, to anticipate events in order to take advantage of emerging opportunities and avoid troublesome events by making decisions from from gleaned facts. The manger must make their decision based on the facts that they would be expected to have at their disposal in order to reach their considered, safe, judgement.

Accordingly, FRMSc recommends training for users of models to understand how the model works, what it does – or does not do – and consequently how to interpret the output of the model to make better decisions.

Models, particularly the System for Aircrew Fatigue Evaluation (SAFE) may be able to accurately predict the likely fatigue of aircrew as, in the case of SAFE, it has been validated against a huge data-set collected from real, live, flight deck crew during their real duties. However, other models may be generalist and not validated against any occupational data so users should check their choice of model is robustly validated for their application.

All models will not take into account individual differences such as lifestyle and whether subjects are naturally so-called owls or larks. Accordingly, model data always needs interpretation; there are so many variables not included in the models that need consideration and no two models are the same.

As companies move from prescriptive Flight & Duty Time Schemes to managed alertness (FRMS) methods an algorithm/model becomes a useful investment.  Though its use is not mandated by any regulatory requirements, it is just so much more pragmatic, effective and productive to use a model in day to day operations.

A model may also be seem by manager and employee as an independent arbiter of any dispute over levels of fatigue. A company that uses one can demonstrate duty of care for the employees and thereby improve industrial harmony leading to higher operational performance

FRMSc uses two bio-mathematical models, which can be made available to customers for ongoing use:

1. The Fatigue Risk Index (FRI), developed by QinetiQ and Simon Folkard Associates for the UK Health and Safety Executive,

2. The System for Aircrew Fatigue Evaluation (SAFE), initially created by QinetiQ and UK Civil Aviation Authority and developed further by FRMSc.

FRI is a general model suitable for any shift work where time zone transitions are not experienced.  The model may be used for employee groups such as health workers, miners, nuclear production staff and production shift workers.

Alternatively for the aviation industry, SAFE is designed and validated specifically for Flight, Cabin Crew and Engineers flying across timezones.  Businessmen will find it useful too.

SAFE has been validated against a huge data-set provided by pilots from a good cross section of the aviation industry and is accepted as the premier product in its class

Please contact us if you would like licensed access to either model