What is the condition under which an RNAV system can be used for IFR flight?

An RNAV (Area Navigation) system can be used for IFR (Instrument Flight Rules) flight under the condition that it has been approved by the Major Command (MAJCOM). This approval ensures that the RNAV system meets the necessary operational standards, safety requirements, and performance criteria set by the aviation authority and military regulations for flying under IFR conditions. Approval by MAJCOM is crucial for ensuring that the equipment has been verified for its intended use, especially in the context of the precision and reliability required for IFR operations.

The other options do not correctly reflect the requirements for RNAV systems in IFR flight. For instance, certification for VFR operations does not pertain to IFR flight standards. The requirement for installation in all aircraft is impractical, as not every aircraft is required to be RNAV equipped for IFR flight; it varies based on mission and aircraft capabilities. Similarly, updating the RNAV system quarterly is not a standard operational requirement for IFR flight approval. Thus, MAJCOM approval is essential and indicates that the RNAV system can properly support IFR navigation and operations safely.