An aircraft equipped with an Inertial Navigation System (INS) flies with INS 1 coupled with autopilot 1. Both inertial navigation systems are navigating from way-point A to B. The inertial systems Central Display Units (CDU) shows: - XTK on INS 1 = 0 - XTK on INS 2 = 8L (XTK = cross track). From this information it can be deduced that:
the autopilot is unserviceable in NAV mode.
only inertial navigation system No. 2 is drifting.
only inertial navigation system No. 1 is drifting.
at least one of the inertial navigation systems is drifting.