On March 4, 2006, about 0930 Atlantic standard time, a Piper, PA-18, N2875D, registered to and operated by Aerial Sign of Puerto Rico, as a Title 14 CFR Part 91 banner towing flight, ground looped during landing at Isla Grande Airport, San Juan, Puerto Rico. Visual meteorological conditions prevailed, and no flight plan was filed. the commercial-rated pilot was not injured, and the airplane incurred substantial damage. The flight originated in San Juan, Puerto Rico, the same day, about 0910. The pilot stated that after landing at the appropriate airspeed without the banner on runway 9, she applied appropriate airplane control corrections to maintain the airplane on the runway centerline, but immediately after touchdown a strong gust caused the airplane to ground loop to the right. She said that she applied control corrections to counteract the wind, but the airplane did not respond. The left main landing gear collapsed, and the left wing incurred damage. The pilot said that there were no preaccident anomalies with the airplane or any of its systems.