Is there any legal requirement to display the approach plate for an IFR approach? Typically it's briefed as part of the descent checks and then kept on display - but I'm struggling to find any legal requirement to keep it visible.
If you can't find any language for that sort of thing there probably isn't any. At some point the value of regulations ends and you have to let common sense and good airmanship prevail.
Under US 14 CFR 91, I am aware of no requirement for the plates to be on display. The regulations do provide that the chart should be available, however.
One might ask themselves, prior to putting the charts in the case behind the pilot's seat...what would the accident review board have to say about this?