A main reason for the operators not responding properly to state changes is that they do not find the controls that should be used to operate the safety features. In practice, the problem is that there are too many of them, and the operators fail to find the ones adequate for the situation (as was the case of the operation in the 1977 NYC blackout).

Definition

Mode confusion is an incidence following operator's activity, while operating out of the design scope, due to assuming a wrong mode.

Direct function activation

  If the function depends on the scenario, then direct control activation is error prone. Therefore, if direct function activation is desired, then a control should be allocated to this function, and should not be shared with other functions.

Examples

• An operator performs a maintenance procedure when the system is in functional mode (such as production).
• The user of a home TV system changes the Sources state unintentionally, and consequently, assuming the wrong mode, s/he cannot find a particular station ( more).

Mode violation

Mode confusion often results in applying the wrong function, when activated using a shared control .

Mode confusion often results in relying on the wrong data, when displayed using a shared display .

Mode violation can also result from condition sharing, when the operators forget to change the condition before activating the control, or viewing the display.

Updated on 31 Dec 2016.