ERROR MANAGEMENT: Active and Reactive
Active and reactive monitoring. The dual path to success. How can navigation systems help a single watch-keeper “manage” human error before it results in a serious incident? The answer lies in a happy alliance between pro-active and reactive techniques.
A vailability and sophistication of navigation systems vary from bridge to bridge, but it is possible to divide the various techniques designed to cope with human error into two broad categories: proactive and reactive. Proactive techniques relate to the active monitoring of critical navigational parameters. Reactive techniques are more about managing the automatic alerts generated by navigation systems.
A single watch-keeper is able to combine both reactive and proactive techniques for each operational function he or she performs on the bridge. As an example, let us consider the various techniques related to collision avoidance, route monitoring and route control.
Collision avoidance
On modern radars which integrate AIS, it is possible to set a common Closest Point of Approach (CPA) and Time to Closest Point of Approach (TCPA) threshold for both ARPA and AIS targets. This limit can mitigate the possible consequences of overlooking a radar echo/AIS target on a collision course at relatively close distance. Used in such a way, the CPA/TCPA limit and its associated alarm can be considered a reactive technique – you are using the technology to alert you to a situation that is becoming hazardous. However, CPA/TCPA can also be set to perform ‘defensive navigation’, where the watch-keeper establishes a minimum distance to be kept from any targets, in order to prevent hazardous situations from developing. Set like this, CPA/TCPA limits are used proactively.
It is possible to let the radar acquire an AIS sleeping target (that has not yet been activated by the watch-keeper) automatically when it moves inside the set CPA/TCPA limits. Less obvious is the functionality of modern radars, where an ARPA target is merged with an AIS activated target if the two are within the distance, course and speed limits set by the watch-keeper. This merge results in a single target being shown on the display (either ARPA or AIS), with the other one being compared in the background, but remaining invisible to the user.
If, all of a sudden, both targets are shown on the display, it means that the tracking difference between them has gone outside the set merge limits. Used like this, the merge limits become a proactive tool for early detection of potential anomalies in AIS or ARPA target tracking.
Route monitoring
Several ECDIS and radar functionalities can also be employed to manage a solo watch-keeper’s errors while monitoring the ship’s progress. Whether they are used proactively or reactively depends on the operational concept adopted. Take, for example, the off-track alert, triggered once the ship’s Consistent Common Reference Point (normally the conning position) goes beyond the planned track limit. If the track limit is set closer to shallow waters than to the planned track, the off-track alert can be used as a reactive tool to make the operator aware of imminent danger.
On the other hand, the same threshold can be set reasonably close to the planned track to act as the limit of a watch-keeper’s ‘comfort zone’ in normal operations. Now, the off-track alert can be considered a proactive tool that warns the watch-keeper that a heightened level of attention is required when he/she is going off-track for any unforeseen operational reason. The same concept can be applied to radar Parallel Indexes and clearing bearings.
Route control
When available, Track Control Systems can be used proactively to manage human errors related to conning the ship. A Track Control System can be seen as an additional team member on the bridge, in charge of keeping the ship on-track within pre-planned ‘comfort zones’. In addition, the Track Control System allows the watchkeeper to carry out controlled turns. This means that turns can be trialled before being executed by means of a Curved Heading Line adjusted by the operator with the desired turn radius. Controlled turns may well help single watch-keepers prevent errors in giving manual helm orders while busy with other, competing tasks, as they can see the likely result of manoeuvres before they are made.
The use of Track Control Systems, like any other automated tool, opens the door to different types of errors. The most common of these are related to overlooking settings affecting the track-keeping accuracy, i.e. rudder economy, rudder limit and loading condition. So, how can we manage the consequences of such errors? The answer lies in a concept known as ‘active monitoring’. This type of monitoring consists of a pro-active, cyclical visual scanning of critical navigational parameters, rather than simply monitoring alerts – that is to say, actively looking at the information, rather than waiting for the alerts to tell you something is wrong.
Active monitoring of speed, cross track distance, drift angle and the aforementioned settings should be performed at regular intervals. Read the values observed out loud, even if you are acting alone on the bridge. This not only allows early detection of problems, it also enables the watch-keeper to take over manual controls, if required, without becoming ‘out of the loop’ with the related automation. Active monitoring is not just desirable when operating a Track Control System. It is a technique that can be applied to all instrumental navigation tasks to help overcome the risk of overreliance on technology. In conclusion, defensive navigation, automated track-keeping and active monitoring are all key proactive techniques that can help prevent errors from occurring in the first place. Radar, ECDIS and AIS alerts are often used more as reactive tools to mitigate the negative consequences of an error that has already been made. This slight, but very important distinction underpins the two faces of error management doctrine: ‘error reduction’ and ‘capture of error consequences’.
‘All available means’
To quote a well-known expression in our industry, ‘all available means’ should be used by the single watch-keeper to manage his/her own errors. Increasing levels of technology and automation on ships’ bridges mean that effective error management techniques will require a deeper understanding of multiple complex navigation systems, as well as higher levels of awareness of our vulnerability to human errors and their potential consequences.
A SINGLE WATCH-KEEPER IS ABLE TO COMBINE BOTH REACTIVE AND PROACTIVE TECHNIQUES FOR EACH OPERATIONAL FUNCTION HE OR SHE PERFORMS ON THE BRIDGE
Author: Antonio Di Lieto MNI
Captain Antonio Di Lieto has sea-going experience as hydrographic surveyor, Master of a hydrographic vessel and cruiseship officer. He currently works as a simulator instructor at Smartship Australia in Brisbane, where he facilitates port development projects and trains Australasian port pilots. Antonio’s present professional interest is in bridge design, human factors and instrumental navigation technologies.