The FBI and the Homeland Security Department are warning about small airplane terror threats just days before the 10th anniversary of the 9/11 terror attacks, but authorities say there is no credible or specific information about a plot.

The FBI and DHS say as recently as early this year, al-Qaida considered ways to attack the aviation sector because it would have a greater impact than other means of attack. That’s from a Sept. 2 bulletin obtained by The Associated Press.

The bulletin was sent to law enforcement and private officials around the country but was considered routine. The five-page document described al-Qaida’s continued interest in recruiting Western terror operatives to get training on flying small aircraft.

Federal and local law enforcement have increased security around the country before the anniversary.