The SAFE Model

THE SAFE MODEL

SAFE is an acronym for the System for Aircrew Fatigue Evaluation: a computer program that includes a suite of algorithms that allow a range of factors influencing alertness in aircrew to be evaluated.

It has been validated for use by the airline industry from a huge data set that has been compiled over decades of studies with commercial aircrew.

safe-model

The model takes inputs of many thousands of pilot schedules and returns fatigue scores every 15 minutes throughout each duty period, taking into account trans-meridian travel, cumulative fatigue, crew composition, on-board napping and other variables. SAFE estimates sleep periods – both start time and length – and these can be manually adjusted as part of the interactivity that is designed into the model in order to find optimum solutions for problematic rosters. Sleep periods can also be inserted, changed or deleted.

FEATURES AND BENEFITS

The benefits and features of using SAFE are:

It is The Standard model that is validated specifically for the aviation industry and is used by many major airlines world-wide.
It is used by many regulators including UK Civil Aviation Authority, CASA (Australia), CAAS (Singapore) and GCAA (Dubai) to assess applications for flight derogation. Using the same tool for internal assessment before submitting the case for derogation makes complete sense.
It is very easy to use: the model works with very few inputs; indeed as few as just duty start and finish time; start and finish airport and number of sectors (legs) flown during the duty for a 2 pilot crew. For augmented flights, in flight rest data is required for long haul and ultra-long haul duties. Partially augmented duties are also catered for as are in-duty rest periods for split shifts.
It accommodates time zone travel, changes to circadian rhythm and cumulative fatigue. It predicts likely sleep patterns – these are displayed automatically.
It allows rapid assessment of rosters to highlight problematic areas for further investigation.
It supports ‘what if’ scenarios: can interact with the model to change crew composition, in flight rest and sleep periods to reflect individual behaviours.
It has a simple and powerful display for the analysis results: problematic areas are easy to identify and optimise.
It is exceptionally useful for incident investigation to estimate likely fatigue at a particular time during a particular duty when the incident occurred.
Using a bio mathematical model is a relatively inexpensive way of identifying the hazards within planned and actual rosters. The Return on Investment is high with a very short payback in comparison with identifying hazard any other way.

USING SAFE

SAFE can be used to assess planned or actual rosters; exploration of new routes or operations such as Ultra long haul; or used as an investigative tool after an incident to determine the likely fatigue of the aircrew at the time of the incident.

Once any problematic duties are identified, change may be explored quickly and easily using the interactive features of SAFE. For those duties that continue to be problematic a fatigue study may be suggested to explore and measure the hazard more closely.

The SAFE and CARE models require a very small number of inputs to assess the likely fatigue and returns a score every 15 minutes of duty. Data can be input either manually or using a spreadsheet or an API interface module may be embedded into the roster generation software suite to feed the model automatically. This is a very productive way to use these models.

Download this paper on Automated Collection of Fatigue Ratings at Top of Descent by David Powell, Mick Spencer and Keith Petrie as an example of how SAFE may be used in airline operations.

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