Airplane expenses arise from high fixed costs, particularly for pilots and depreciation. However, on a 'per-mile' basis the airplane used in line patrol is no more expensive than equivalent patrol on the ground. It is superior in terms of area patrolled. However, as used now by the Illinois State Police, the airplanes have not proven cost-effective in terms of costs incurred for activity rendered, mostly because the aircraft have not been used to their fullest capabilities. Aircraft are being operated 800 hours per year, substantially less than they could be. At a 50 percent increase, the fully allocated costs would decrease approximately 25 percent. Costs per action of the line patrol can be reduced by increasing both the number of stops for traffic violations and the number of motorist assists each hour. This increase may require dedicated patrol to certain segments of the Interstste Highways and does require a greater availability of ground personnel--therefore, greater administrative and supervisory control of the assisting personnel on the ground. Airspeed operations can be more productive. In the air speed mode, the supervisor would be responsible for pulling the vehicles and obtaining the drivers' documents. The supervisor would turn over the information to a trooper who could complete the citation. An increase in productivity with four cars from 2.7 stops per hour to 4.0 stops per hour would decrease the cost per stop by 30 percent. Thus the cost of maintaining aircraft for the specialty functions can easily be offset by the continuous use in daily traffic operations. Eleven references and extensive graphs and tables accompany the text. An appendix shows the data used for the calculations. (Author abstract modified)