Thanks Tom. I'm using Gmax and my opacity setting for the prop_slow and blurred material is set at 99% although I've tried it at 95% too. The result is the problem in the screen shot.
I've saved the texture as Dxt3 but I've also tried what I think is the Microsoft format for the DC-3 props which is 32bit (I presume 888-8). That still creates the drawing order problem, although not for the default DC-3.
I'm not clear whether the prop texture should have the "_t" suffix for transparency. Could you just advise on the right texture format please?