The most common agricultural aircraft are fixed-wing – such as the Air Tractor, Cessna Ag-wagon, Gippsland GA200, Grumman Ag Cat, PZL-106 KRUK, M-18 Dromader, PAC Fletcher, Piper PA-36 Pawnee Brave, Embraer EMB 202 Ipanema, and Rockwell Thrush Commander – but helicopters are also used.In places where dedicated use as an agricultural aircraft is uneconomic, utility types such as the Antonov An-2 biplane and De Havilland Canada DHC-2 Beaver have been used.In the case of helicopters, tanks are placed on or outside the body of the aircraft, while a spray rig, extending outward to the sides, is attached well below the main rotor blades.Aerial spraying has been controversial since the 1960s, due to environmental concerns about pesticide drift (raised for example by Rachel Carson's book Silent Spring).It is now often subject to restrictions, for example spraying pesticide is generally banned in Sweden, although exceptions can be made such as for an area plagued by mosquitoes during summer.