You're called to the flight deck B747 Classic. Capt's HSI showing the compass flag. You do all the normal, easy things, no help. Normal easy defined as: HSI, Compass coupler, INS and tried fiddling with the INS/Radio switch. Again, No help.
No significant history in the navigation system. What catches your eye is that this aircraft had a #2 & #3 electrical systems fail due to a split breaker meltdown and to make matters worse the #2 engines experienced an IFSD enroute to your station. All thise pesky problems have been fixed.
A little far fetched but we have had the compass problem gere and at previous lives. The second part is the set-up and hint.