What is one limitation when filing a random RNAV route on an IFR flight plan?

Answer: B — The entire route must be within radar environment.

When filing a random RNAV route on an IFR flight plan, one significant limitation is that the entire route must be within a radar environment. This requirement exists because air traffic control needs to maintain situational awareness and provide safe separation between aircraft operating under instrument flight rules. Utilizing radar allows for real-time tracking of aircraft positions, which is critical for ensuring safety when flying on a non-structured route. Flying a random RNAV route typically involves using waypoints that may not be associated with traditional airways. In these scenarios, radar coverage is essential to monitor the flights effectively and manage air traffic efficiently, especially in areas where other aircraft may be flying nearby. The requirement for radar coverage ensures that air traffic controllers can provide timely information and guidance to pilots, particularly during critical phases of flight, such as takeoff, landing, and in busy airspace. The other options pertain to different constraints but do not accurately reflect the critical radar limitation associated with filing random RNAV routes in IFR operations.