Originally Posted by
Zar_1
What I think: Maybe the TCAS was in RA Mode on one of the planes (Unlikely, since it would be apparent on the MFD)
Or... maybe more probably: The TCAS systems were configured slightly differently with different parameters/software versions
Well, in my case they were both company aircraft with identical TCAS units as far as I know. If one of them was in TA mode, you’re correct that they would see it on the PFD and they would not have TCAS blue on the PFD either.