code: def vtas2cas(tas, h):
      
      p, rho, T = vatmos(h)
      qdyn = p*((1.+rho*tas*tas/(7.*p))**3.5-1.)
      cas = np.sqrt(7.*p0/rho0*((qdyn/p0+1.)**(2./7.)-1.))
  
      # cope with negative speed
      cas = np.where(tas<0, -1*cas, cas)
      return cas
docs: tas2cas conversion both m/s