It was a Dash 8. It was several years ago that it happened, but I think the radalt wasn't sending any info at all to the TCAS so the TCAS low level inhibits weren't active. I don't know enough about that specific system to know how likely it is to happen again. Airline pilots fly with stick pushers that are also capable of pushing the nose towards the deck at low level but a bit of fail safe engineering makes that very unlikely. We have five seconds to respond to an RA, if a fully automated system announced the RA then paused for a couple of seconds prior to flying the manoeuvre then we'd have a reasonable chance of disconnecting the autopilot in time to prevent an unsafe RA.