The Burbank and Glendale Police Departments in California operate their own aircraft. However, they do so out of a single hangar. The facility construction costs and day-to-day operating expenses are shared 50/50.
Each department has its own mechanic, but the mechanics help each other out when needed at no charge. Each agency owns its own aircraft, but they're from the same manufacturer, so the crews can easily train together. The officers on the Burbank and Glendale air support units stagger their patrol shifts to ensure that one aircraft is up at all times, and the crews respond to radio calls in both neighboring cities. And in a pinch, the Tactical Flight Officers from one agency can fly in the other agency's aircraft.
The Southern California cities of Costa Mesa and Newport Beach have taken it one step further, operating one of the smoothest joint operations around. The cities' police departments operate a single air support unit via a Joint Powers Authority (JPA). It took a while to get through all the legalese, but for the last seven years the unit has thrived.
Each agency provides pilots and TFOs, as well as on-site mechanics. The mechanics also provide contract maintenance to the Orange County Sheriff's aviation unit. The unit owns three turbine aircraft, with an envious aircraft replacement program.
Every 3.3 years, the oldest aircraft is replaced with a new one. This can be accomplished because both agencies put money into an account at a rate that will enable them to fund an aircraft purchase every 40 months. Without this kind of planning and vision, agencies will be forced to come up with a huge chunk of money whenever they want, or need to replace, an aircraft. A board of governors oversees the unit, and representatives from both agencies serve on the board.