Do not, 'under any circumstances', open that door. = 'Under no circumstances' are you to open that door. [=no matter what happens, do not open that door]
Due to 'circumstances beyond our control' [=things that have happened that we cannot change or influence], the flight is canceled.
She says that her client is 'a victim of circumstance' and should not be blamed for the accident.
(..) Here's what you do. Open her mouth, take a handful and throw it at her. Whatever sticks, that's the correct dosage. Under no circumstances are you to compromise our no-talking agreement. Dr Kelso is always saying... I'm gonna say this as carefully as possible, so I don't overstate it. (..)2001 TvShow: Scrubs Title: My First Day Season: 1 Episode 1