Read the two articles:
https://www.thestreet.com/story/14475330/1/what-to-know-about-trading-halts-in-case-this-selloff-gets-even-nastier.html
http://www.sandiegouniontribune.com/news/sdut-californias-worst-power-failure-started-arizona-de-2011sep08-story.html
How do the principal properties of dependability come into play with either of these systems? Why is it important to consider all the principal dependability properties when evolving software into new capabilities