Managed descent, altitude constraints, radar headings
You're on a prescribed RNAV arrival, Approach clears you to the IAF and clears you to descend to the IAF altitude, reminding you to meet all altitude constraints along the way. You dial in the altitude given and are happy because you checked and briefed all constraints 10 mins before. Your monitoring is good, the correct modes are engaged yet the old boy on the left mumbles something under his breath. You know what he's thinking, but as it's not illegal to fly the plane like this he lets you be.
About 20 miles before the IAF, you get a radar heading, your lateral mode change results in a vertical mode reversion (On Airbus its Open Descent on Boeing... FLCH?). The heading takes you towards high terrain and the cleared to altitude is no longer appropriate. Old boy then chimes in with "Hah! This is why I don't enter the next altitude until I'm 200ft away". Just as he says that, ATC gives you a better heading to stay clear of terrain as they should and as is one of their responsibilities.
I would like you to imagine this kind of day out and offer your views on the situation particularly with regards to automation, trust in automation, monitoring, ATC.
Thanks!