Crab - I PM'd; if there is a need, I will post answering your questions. At the moment I see no reason to enter into a debate about the quality of the risk assessment.
Before I attempt to address Helicomparator's point, I have to admit that I had fooled myself into thinking that there would be a major discrepancy in the relative position of the rig (in the FOV) between the 'offset' and 'divergent' approaches - my intuition was wrong.
It is difficult to do any maths because the 'offset' distances are not yet established; however we can make assumptions which will not be wildly in error. If a 10 degree heading change is made at the OIP (1.5nm) the divergence would take us about 490m abeam the rig (we don't actually get to that point because the procedure always requires a turning missed approach at 0.75nm). We can assume that this is the miss distance for the 'offset' procedure - if it is further than this, the differences increase.
At DR/MAPt (0.75nm = 1390m from the rig) with the divergent procedure, the rig will appear at just over 20 degrees to one side (10 degrees relative from the rig + the 10 degree of the divergent heading) and the track-offset will be 250m. With the 'offset' procedure the rig will be seen at (just over) 20 degrees (all of it relative to the rig) and the offset would be 490m.
If it was necessary to position the aircraft back onto the into-wind track, the 'offset' procedure would take more manoeuvring than the divergent.
With a DR/MAPt of 0.5nm (926m from the rig) the position of the rig in the FOV would be respectively 31 v 32 degrees and the track-offset would be 338m v 490m; the 'divergent' would be 20 degrees out of wind and the 'offset' 30 degrees. For both procedures the position of the rig in the FOV (now possibly to one side of the windscreen), the additional manoeuvring, plus the reduced distance for deceleration raises issues.
If you want to see this in diagramatic form draw a rectangle of sides 2778 and 490 with a line (from the OIP) joining the diagonals; put the rig at one end of the 2778 line and the OIP at the other; take two arcs of length 1390 (0.75nm) and 926 (0.5nm) from the rig and intersect the diagonal and the outer line; enter the offset distances/angles I have provided.
Jim
Last edited by JimL; 17th Aug 2009 at 15:11.