Can a pilot fly IFR if their currency has expired?

A pilot cannot legally fly under Instrument Flight Rules (IFR) if their currency has expired, regardless of whether they are flying solo. Currency requirements for IFR operations include having completed a certain number of instrument approaches, holding at least the appropriate endorsements, and meeting the recent flight experience requirements outlined by the Federal Aviation Administration (FAA). When these requirements are not met, the pilot is considered to be out of currency and is therefore not authorized to operate an aircraft in IFR conditions.

While some other answers may suggest scenarios where a pilot might operate under IFR despite expired currency, these do not comply with FAA regulations. Safety pilots, checkrides, or solo flight do not circumvent the fundamental requirement for an instrument-rated pilot to maintain their currency. Therefore, the only lawful situation is to refrain from flying IFR until the necessary currency has been restored through proper training and flight experience.