Which description best applies to Preferred IFR routes?

• A. These routes are published only for international flights.
• B. IFR clearances are issued based on these routes.
• C. Preferred IFR routes are listed in the Chart Supplement U.S. and are used to increase system efficiency and capacity, with weather avoidance procedures dictating otherwise.
• D. They are not applicable to en route planning.

Answer: (C)

Preferred IFR routes are recommended en route paths published to improve air traffic system efficiency and capacity. They’re listed in the Chart Supplement U.S., giving pilots and ATC a reference for routes that facilitate smoother flow of traffic. When conditions permit, ATC will assign or clear you along these routes to optimize spacing and capacity. However, weather avoidance or other operational constraints can require deviations, so a different route may be assigned if necessary. These routes apply to IFR operations in U.S. airspace and are considered in en route planning, not just for international flights or for being the sole basis of an IFR clearance.