gear won't retract is a favorite of mine.
Put the destination on the other side of the alps.
Oil press slowly decr. could be fun too. Especially on 4 engine a/c.
Wx barely minimum at all nearest airports, good at the destination and sick pax.
Fuel leak.
Lofts are all about decision making and crm. Anything that is not an emergency or anything that doesn't have a checklist for or anything that doesn't specifically say 'land at nearest suitable'.
Another item is combinations, see that you get the full picture, including landing, g/a and diversions. Primary brake loss plus slippery rwy is a good one.
Another could be dispatch with no steering, wind just at the tailwind limit and the other direction landing would require backtrack.
Endless possibilities...