How would you handle a situation where a design flaw led to a serious accident?

Hopefully something like this never happens to you in your career as a civil engineer, but one of the biggest ethical dilemmas you may face is how to handle a situation where your error or your firm's error led to a serious accident or structural failure. Engineers are called on to take responsibility for their work -- even when something goes wrong. Especially when something goes wrong. Show that you're a stand-up engineer by offering an honest, ethical answer.