Rasmussen’s SRK Model

This model describes human behaviour and decision making in a man-machine environment and the resulting errors. It is a standard model used in aviation and was developed by Jens Rasmussen, a Danish professor for system safety and human factors.

Rasmussen-SRK-model

The basics of the SRK model

The model is about cognitive activity during a decision making process. It defines three different levels of activity:

  • Skill based level
  • Rule based level
  • Knowledge based level

Depending on the experience of a pilot and the task to be fulfilled, either one, two or all three levels are ‘active’ during a decision making process.

But what does it mean exactly?

Skill based level

This level is all about routines and automatisms. It is the most ‘basic’ level in a decision making process.

In aviation it can be seen as the ‘aircraft handling’ level. It is the level of manual flying and is highly linked to good practice and flight training. Most decisions are based on what a pilot has learned during training and practicing and usually has a ‘reactive character’.

For example:

When the stall warning becomes active during a climb usually pilots will push the controls and decrease the angle of climb in order to gain speed.

Rule based level

This level is about procedures. It is a ‘higher’ level in the decision making process since the cognitive capacities required are higher.

In aviation it does not mean simply following the checklist / procedure (the rule how to do it), it also means if there is no obvious rule, pilots will ‘look’ for their own rules based on past experience.

For example:

A rough running engine in a general aviation aircraft leads the pilot to call for the emergency checklist and work through it.

Knowledge based level

This is the ‘highest’ level in a decision making process. It is about handling unknown / novel situations.

In aviation this would be handling non-standard emergencies. There have to be a lot of factors included in the decision making process. Useful in such scenarios is the FORDEC method.

For example:

The emergency landing on the Hudson river. Altough there are certain rules for ditching, deciding for the river involves considering all options, knowing about the risks involved and contiously executing such decision.

Unfortunately there is a ‘BUT’

But: All of the above mentioned levels are prone to error.

Wrong trained skills could lead to wrong actions (skill based level), old checklists could endanger the safest possible operation of the aircraft (rule based level), missing items during the risk analysis could lead to wrong decisions (knowledge based level).

In order to prevent this as much as possible –¬†we assume here that this cannot be completely excluded – pilot training is targeting all 3 levels.

“Being able to conduct perfect landings in all weather conditions only does not make someone a good pilot. It is the mixture of skill, following rules and procedures and knowledge what makes the airman.”

Conclusion

According to Rasmussen human decision making can be split in three different levels.

Each level is prone to error – unfortunately.

Nevertheless, good pilot training is key to safe flying since it will ‘train’ in all levels.

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