On 15 October 2011, a Loganair Saab 340 in uncontrolled airspace and inbound and level at 2000 feet QNH on a procedural non precision approach in day IMC to runway 18 at Stornoway received a TCAS RA DESCEND’ when a second Loganair Saab 340 outbound on the same procedure descended prematurely to the same altitude contrary to ATC clearance. The subsequent investigation concluded that the failure of the controller to re-iterate the requirement to remain at 3000 feet outbound until advised had contributed the crew error. Minimum separation after the TCAS RA was less than 0.1nm horizontally when 500 feet vertically.