The FAA issued NOTAM (Notice To Airmen) FDC 4/2599 on August 12, 2014 creating a no fly-zone around Ferguson. The restriction has been renewed on 8/18 in FDC 4/4815 and will last until 8/25 [source].

The FAA issued the directive at the request of St. Louis County Police and the stated reason was "TO PROVIDE A SAFE ENVIRONMENT FOR LAW ENFORCEMENT ACTIVITIES".

The police explained their request to the FAA by saying that a police helicopter had taken fire the night before.

The original Temporary Flight Restriction went into effect August 12 at  8:15am CDT and expires at 3:00pm CDT Monday 8/18.

The second order was requested by the office of Governor Jay Nixon. It went into effect at 3:00pm CDT 8/18 and lasts until 3:00pm CDT 8/25.