Final answer:
No, it is not allowable to operate an aircraft in controlled airspace under IFR without filing an IFR flight plan, as it is necessary for safety and to provide air traffic control with essential information.
Step-by-step explanation:
The question you've asked pertains to aviation regulations regarding Instrument Flight Rules (IFR) operations within controlled airspace. To answer your question: No, it is not allowable to operate an aircraft in controlled airspace under IFR without an IFR flight plan. All flights that intend to fly under IFR in controlled airspace are required to file an IFR flight plan and receive an air traffic control (ATC) clearance before entering controlled airspace. Filing an IFR flight plan ensures that air traffic control has the necessary information to maintain separation between aircraft and manage the flow of air traffic safely and efficiently. Pilots who fail to file an IFR flight plan may face legal and safety consequences.