On approaching a Normally Unmanned Installation (NUI) one orbit was completed for HLO to clear the deck, he signaled "clear", and deck also seemed clear to both pilots.
Once A/C slowly made contact with the deck with the port main gear it lurched forward, sideways, and rolled left and possibly right also. There was no cyclic movement to cause this to occur. The slide forward (several feet) and roll was significant enough for the captain to come on the controls. The A/C settled on all three landing gear and landing checks were made.
On inspection of the helideck it was found that whilst the hard surface underneath the netting was fairly abrasive, the netting was extremely slippery, it was a hazard to even walk on. The net was covered in a green slime, itself was fairly elastic, and also seemed to be beginning to fall apart. The left wheel had dragged a considerable amount of net with it across the deck, and there seemed to be two slight rubber drag marks on the deck where the right wheel had made contact. The deck was wet on this occasion, later in the day when returning to the platform and when dry the netting was far more effective.
All helidecks, particularly Normally Unmanned Installaitions (NUIs) should be maintained and regularly checked