Offshore rig helideck surface block collapsed, trapping the starboard main wheel. Unclear at present whether the collapse was caused by the wheel or the integrity of the block. Anonymously supplied images can be seen at both links below
The Mariner field is in UK Block 9/11a in the northern North Sea approximately 95 miles east of the Shetland Islands.
The helicopter was freed and flew back to base at Aberdeen on 03-Apr-21