Practical difficulties with Differential Correction Systems
7.6 The Sub-Committee considered the report of the Technical Working Group and noted its comments (NAV 45/7, paragraph 2.15) that there were practical difficulties with Differential Correction Systems in achieving the performance required of resolution A.815(19) - World-Wide Radionavigation System, particularly the update rate of 2 s, the signal availability requirement of 99.8% and the service reliability of 99.97%.
7.7 The Sub-Committee was informed by the IALA representative that discussions had taken place in IALA on the practical difficulties with Differential Correction Systems in achieving the performance required of resolution A.815(19) - World-Wide Radionavigation System.
7.8 Taking into account the fact that some Member States had experienced difficulties meeting the requirements of resolution A.815(19), IALA offered to analyse these standards, including their definitions and levels, and inform the Organization accordingly.
Guidance on chart datums and the accuracy of positions on charts
7.9 The Sub-Committee recalled, that at its forty-fourth session, it had considered the United Kingdom proposal (NAV 44/7/9) for a draft text of an SN Circular containing recommendations/guidelines with respect to the safety aspects of the use of different geodetic chart datums, as discussed by the Technical Working Croup at NAV 43, taking into account the proposal by IEC (NAV 43/7/4), and prepared the preliminary draft text of an SN Circular containing guidance on chart datums and the accuracy of positions on charts.
7.10 The Sub-Committee also recalled that it had also instructed the Secretariat to convey the preliminary draft SN Circular to IHO for consideration and submission of their comments to NAV 45.
7.11 The Sub-Committee was informed by IHO (NAV 45/7/2) that while nearly all the hydrographic offices of coastal States were promulgating guidance on chart datums, they were almost unanimously of the opinion that an IMO SN Circular would be beneficial. France and the Russian Federation felt that an SN Circular would be a duplication of the work done by hydrographic offices.
