Radar data of non-specular meteor trails shows two clear and consistent features: (1) non--specular meteor trails are observed from a narrower altitude range than are head echoes and (2) an approximately 20 ms delay between meteor head echoes and trail radar scatter. This paper shows that both features can result from meteor trail plasma instability. Simulations have demonstrated that trails often develop Farley-Buneman/gradient-drift (FBGD) waves which become turbulent and generate field aligned irregularities (FAI). Plasma stability analysis shows that trails are only unstable within a limited altitude range, matching the observed altitudes of non--specular trails to within 1--2 km. The simulations show that instability develops into turbulence in ~20 ms and appears to be the only meteor trail process that can explain both the observed delay between head and trail echoes and generate coherent scatter at both UHF and VHF wavelengths.