That's correct...good memory! The date was 10/7/12.
Because most people won't be familiar with "flour bombs", let's explain the culture around here...
Scattered around the Tulsa area, there are ~5 airparks. These are "airport neighborhoods" ...places where you can build a home and hangar along a runway. Throughout the year, people at the various airparks hold events such as a brat feed, bean dinner, chicken wings, fly-ins, etc. These are usually for group fundraisers and/or charities. As a fun way to notify your friends at the other airparks about the upcoming event, a group of people from the host airport will fly around and "flour bomb" the other airports. This is just a paper sack filled with flour dropped from a plane. People come out of their houses to watch the planes drop the bombs. It's all in good fun, and the flour/paper disintegrates with the next rain. In the pics above, we're headed northwest to flour bomb Skyhaven Airpark for the Wingding (chicken wings) event.