What altitude must be used in case of two-way radio communications failure during IFR?

In the event of a two-way radio communications failure during IFR (Instrument Flight Rules) operations, the appropriate altitude to maintain is the last assigned altitude or the Minimum Enroute Altitude (MEA), whichever is higher. This protocol ensures that the aircraft remains compliant with air traffic control instructions while also ensuring safe clearance from terrain and obstacles. The MEA provides both obstacle clearance and adequate signal coverage for navigation aids, making it a critical altitude to know when communication is lost.

Maintaining the last assigned altitude is essential, as it reflects the most recent instructions from air traffic control, which are vital for the safe operation of the aircraft. If the pilot has not received a new clearance or instruction prior to a radio failure, sticking to the last communication preserves the intended flight profile and safety margin. This procedure emphasizes the importance placed on following air traffic control directions and ensuring safety in the airspace system.