My most stressful flight ever was on a F100 as we lost our Nav dsiplays during a dirty dive into Sofia during the Yugoslavian conflict.
A cheap system which would drop out if you lost the two DMEs that it calculated it's position from. Did the same if the two were were on the same axis as the aircraft (gva).
So you had to dive into your briefcase, find the chart, tune the nav aids.....
Similarly the all talking autothrottle didn't work in open descent - we had two stall warnings flying into Nice during visual approaches before it was realised that it didn't do what it was supposed to do.
The first the crews knew that the autothrottle wasn't working was the shakers.
Then it had a useless undercarriage - I grounded an aircraft once to be told by the guy who was responsible for the original acceptance that he had refused the aircraft...SR modified it and Marichetti? Built a new one which failed with the press on board.
Wrong aircraft for a flag carrier.