The F100 although advanced for its time did have drawbacks, many were fitted with AHRS and without adequate DME updating the map could shift quite alot, I do not know of a GPS upgrade for the aircraft and the airline i operated them for had TAWS (EGPWS) fitted some 7 or 8 years ago, it is unlikely that this aircraft had TAWS fitted when new , therefore it is possible that it was retro fitted to this airframe. An NDB approach was not easy although the drift ball and (if well trained) the FPA was useful.
I always remember my sim instructor in the 1990s when converting onto the type preaching that when all the gizmos were starting to confuse and absorb the crew to throw them away and to always remember "its only a bloody aeroplane!" and revert to basics. "the kit although clever is perfectly capable of flying you into a mountain". Wise words.