Non-equity groups are not legal in the UK. The CAA allow up to 20 people to jointly own shares in a group, so the minimum value of a share is 5% of the aircraft. Shares do not have to be equal, but each member of a group must own at least 5% of the aeroplane.
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These groups are sometimes run as companies so none of the members actually own anything, but have a shareholding in the company.