Altitude change  V287-495-500 confluence of airways V520 (even) oriented east/west Victor Airway V23 V595 MRA 9300 No altitude change V287 MOCA *3400 V165 (odd) oriented north/south Altitude change  Figure 1-2.  Victor airways and charted IFR altitudes. Jet routes exist only in Class A airspace, from 18,000 feet MSL  to FL 450, and are depicted on high-altitude en route charts.  The letter “J” precedes a number to label the airway (e.g., J12). Area navigation (RNAV) routes have been established in  both the low-altitude and the high-altitude structures in recent  years and are depicted on the en route low and high chart  series. High altitude RNAV routes are identified with a “Q”  prefix (except the Q-routes in the Gulf of Mexico) and low  altitude RNAV routes are identified with a “T” prefix. RNAV  routes and data are depicted in aeronautical blue.  In addition to the published routes, a random RNAV route  may be flown under IFR if it is approved by ATC. Random  RNAV routes are direct routes, based on RNAV capability,  between waypoints defined in terms of latitude/longitude  coordinates, degree-distance fixes, or offsets from established  routes/airways at a specified distance and direction. Preferred IFR routes have been established between  major terminals to guide pilots in planning their routes of  flight, minimizing route changes, and aiding in the orderly  management of air traffic on Federal airways. Low and high  altitude preferred routes are listed in the Airport/Facility  Directory (A/FD). To use a preferred route, reference the  departure and arrival airports; if a routing exists for your  flight, then airway instructions are listed. Radar monitoring by ATC is required on all random  RNAV routes. These routes can only be approved in a  radar environment. Factors that are considered by ATC  in approving random RNAV routes include the capability  to provide radar monitoring and compatibility with traffic  volume and flow. ATC will radar monitor each flight;  however, navigation on the random RNAV route is the  responsibility of the pilot. Other Routing 1-5