From March 2005, SACs in technical trades who had attained the Operational Performance Standard were given a new badge of rank, consisting of the three-bladed propeller inside a circle. This new rank insignia was introduced, at least in part, to distinguish airmen trained to work unsupervised from those who were not, although in practice under the old rank structure long serving and competent SACs would often carry out some of the technical duties that were designated as JT duties; this was mainly due to the large numbers of SACs waiting for fitters' courses to enable promotion to JT.