Finger trouble?
Enter one minute error in Longitude (roughly 67 n.m) and the three IRUs find they are no longer at the last position in which they were shut down. The align lights flash. Re-enter the same coordinates and the IRUs are informed that they have been moved to a new location in the meantime, so they accept that as the new starting position. Now get airborne and the FMS begins position checks and cannot resolve the differences. The FMS shuts down and blanks the Nav displays - NCD.
Nothing to do now but select ATT, enter heading from the standby compass and cry for help from ATC.
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Through difficulties to the cinema