Mr. Reynolds is correct. We've just got a new software update to verify in a Northrop-Grumman (Litton) LTN-101 with 2005 Mag model. This is on the CRJ but it's the same unit & SW for majority of Airbus'
AFAIK.
Inertial input is required for "coasting" (when no valid GPS solution available) for AC90-101 SAAAR ops.