Those flash crashes serve the purpose of allowing the brokers to buy up shares from everyone who was stupid enough to put a STOP LOSS order in place.
In the chart below, AAPL never "really" fell below $533. But if someone had a STOP LOSS at $533, the flash crash allowed the brokerage to steal the shares at $526 before bouncing the price back to $533 a few seconds later.
It's quite a gimmick. It's also what cost me my AOL shares a decade ago.
Lesson learned? Always use a STOP LIMIT, not a STOP LOSS. In this example, a STOP LIMIT at $533/531 would have said to "sell shares if $533 is reached, but only if a price of $531 or better can be obtained."
It makes a world of difference.

Gold is $1,581/oz today. When it hits $2,000, it will be up 26.5%. Let's see how long that takes. - De 3/11/2013 - ANSWER: 7 Years, 5 Months