Source : http://nos.nl/l/tcm:5-1421855/ (en neerlandais) septembre 2012
According to news reports, three airplanes were flying in formation when the incident happened. Two Aviat Huskys had been towing banners along the beach for rival political parties. The third airplane, a Cessna 172, was filming and photographing one of the Huskys when it collided with the other.
The main gear of the 172 struck the left wing of the Husky and became stuck. After about 10 seconds the airplanes managed to separate. The Husky landed on the beach with a damaged left wing and flaps (including two large holes from the other airplane’s tires), while the 172 flew to nearby Rotterdam Airport where it performed a flyby so the tower could check if its gear was still in place. It made a normal landing as rescue crews stood by.