Route south along the Bangor Way to Tawnyanruddia.
This was the plan B route for the day; the original intention had been to take in both Slieve Carr and Tawnyanruddia. My reccy out to the east to survey the possible descent however, was not promising. Descending off the northern spur of Slieve Carr would have left me with about 5k of completely level, utterly wet bog, riven equally with hags and water. Even from the start I knew this would not be a promising finish to the day.
Simon3 originally mentioned this starting point on the Slieve Alp page, as being one possible route to Slieve Carr from the west. I'm sure it is possible but I'm equally sure it wouldn't be fun, The terrain around here, particularly when wet, is bad enough anyhow. What I saw under Slieve Carr looked far worse.
The route as walked heads south on the Bangor Way for about 6-7k before leaving the way to summit Tawnyanruddia and returns the same. The term 'Way' should not give you much confidence; it's use is entirely relative to the surrounding terrain.