The operational modes

The exceptional situation is defined by a combination of modes belonging to two mode sets :

• The primary mode set: the operation was for navigation, maintenance, etc.. Therefore, the operation mode was a member of the mode set (Navigation, Maintenance, ...)
• The steering mode set: the mode set was controlled by the steering lever, which had three modes: Manual, Automatic, Control.

  In the Control mode, the rudder was disconnected from the wheel, disabling the controlling of the ship's direction. This mode was designed to enable certain maintenance procedures, which were rarely used during normal navigation (if at all). However, in this incidence, the Control mode was set unintentionally .

  The failure in this case study is attributed to scenario ambiguity, due to implicit setting of the navigation mode.

  To enable identification of scenario mismatch, the modes should be defined explicitly, and the Scenario analyzershould verify that they match.

  Guidelines about mode setting

Updated on 18 Apr 2016.