Receiver autonomous integrity monitoring (RAIM) continuously monitors and compares signals from multiple satellites to ensure GPS signal accuracy. When you fly IFR using a non-WAAS GPS as your primary navigation system you are required to do a RAIM prediction check for your route before each flight. If RAIM is predicted to be unavailable, you must use other navigation systems or delay or cancel your flight.
The basic formula for planning your descent is to divide the altitude you need to lose by your desired rate of descent, for example 3,500 feet divided by 500 feet per minute equals 7 minutes.
The RFD VOR was deactivated on October 7, 2021, as part of an FAA plan to discontinue 307 VORs across the U.S. national airspace by 2030. For more information and a complete list of VORs targeted for discontinuance go to this web page: https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/techops/navservices/gbng/vormon/