WAYPOINT - Comparing the bigger picture
Dr Andy Norris, an active Fellow of The Nautical Institute and the Royal Institute of Navigation, compares VTS and marine communications with the specifics of Air Traffic Control.
Comparisons between the air and maritime transport worlds are rarely made. This is probably because their main strengths and weaknesses are so obviously different – but complementary. One exception to this is the comparison between Vessel Traffic Services (VTS) and Air Traffic Control (ATC). Although there are many differences, the concepts are very similar, not least the fundamental reason behind their existence – to help maintain the safety of traffic within a particular area, while making it flow as smoothly and rapidly as possible.
Most air traffic is either entirely or mostly spent on busy routes, and pilots typically have to comply with explicit instructions from ATC operators for the entire flight. This is one of the big differences between ATC and VTS; ships are generally only under guidance from VTS for relatively small portions of their voyage. Another major difference is the level of the guidance given to ships and aircraft. On aircraft, the information provided by ATC can be very detailed, effectively specifying the required altitude, speed and track for the airplane to follow. As a result, some airline pilots cynically consider that navigation is no longer part of their role – they just have to follow the detailed instructions of the ATC operator.
Attention to detail
In the maritime world, VTS concentrates on providing real-time safety information to vessels, rather than requiring them to follow detailed instructions concerning their course, bearing and speed. VTS may provide instructions to vessels, but these must be results-oriented. Unlike the Master and Pilot, the VTS is concerned with the overall safety of the waterway, rather than that of a specific vessel; that is the affair of the team on board. VTS advice never overrides the primary function of the onboard navigating team, which is to maintain safety at all times. This is exactly the same for ATC and aircraft; even though the advice ATC gives is far more explicit, this advice will not override the authority of the pilot of the aircraft.
One of the reasons why ATC guidance has to be more explicit is because of the difficulty aircraft pilots have in getting good visibility of the local situation in all three dimensions. ATC operators generally have a far better view of the overall situation than the aircraft pilot because of their large and well-sited ground-based radars, with aircraft generally flying well above any obstructing radar clutter.
For the maritime case, depending on the VTS area, the traffic image may include additional information from multiple shorebased AIS and radar stations. However, some of the information that is available to VTS operators can be less accurate and complete than that which is locally available to the vessel.
In particular, some small pleasure craft and other floating hazards may be entirely invisible to VTS. While VTS has a better overall view of the waterway, your onboard radars will generally give a better view of the immediate local situation. Even more importantly, the direct view from the bridge windows will be giving the crew on board a unique insight. AIS information is available to both the vessel and the VTS operator.
Safety first
A more difficult situation for ATC is when the aircraft is manoeuvring on the ground. In this situation, local hazards may not be so clearly visible to the ATC personnel and they rely on the pilot and co-pilot to identify and avoid them. This is more like the maritime situation. Interestingly, the role of air pilots in detecting things by eye in close-to-airport situations has recently become far more important because of the possible presence of drones. These would generally be invisible to ATC operators but are highly dangerous to the safety of the aircraft.
The very much slower speed of ships compared to aircraft and the fact that they are generally all at one level – and not at many different depths – means the current approach to VTS is effective. Consequently, improvements to VTS can be aimed at greater efficiency, supporting port access and environmental protection while maintaining safety.
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