Originally Posted by Often1

Although it is clear that it is a violation of law (criminal in some circumstances, merely an $11K fine in others) to disregard crewmember instructions, on this particular one, FAA went to even greater lengths.

When FAA authorized carriers to file plans permitting device usage, FAA expressly noted that at the Captain's discretion, all devices could be ordered to full off without any notice or explanation.

In certain instrument landings where the full capabilities of the aircraft are required, the engineers were unable to eliminate the risk of interference from devices. Thus, the specific rule and its reason.

It is beyond risky and frankly stupid to disregard the instruction. If the FA happened to slip into the old-fashioned mode, so what? If the FA did this intentionally and this was the flight which goes down in low visibility, that's something for the know-it-all's to think about.