If an air carrier airplane is flying IFR using a single ADF navigation receiver and the ADF equipment fails, what must the flight be able to do?

When an air carrier airplane is flying under Instrument Flight Rules (IFR) with a single Automatic Direction Finder (ADF) navigation receiver and that equipment fails, it must be able to proceed safely to a suitable airport utilizing other navigation aids available. The option that specifies proceeding safely to a suitable airport using VOR aids and completing an instrument approach by means of the remaining radio system is correct.

This aligns with the regulations governing IFR operations, which stipulate that in the event of a navigation system failure, pilots must still have capabilities to navigate and communicate effectively to ensure a safe landing. Using VOR (VHF Omnidirectional Range) aids allows the flight to maintain navigation and manage its approach, even with the loss of the ADF system. This approach emphasizes safety and compliance with IFR regulations, allowing the pilot to still execute an instrument approach and land the aircraft at a suitable airport.

Other options may suggest less effective or safe means of navigation that do not fully leverage available resources or could lead to situations where the aircraft is less capable of ensuring safe operations during such equipment failure. It is crucial for pilots to utilize the remaining navigational aids effectively to ensure the safety of the flight and fulfill operational requirements.