In 1921 he distinguished himself for having saved the new airship Roma, just completed and ready for delivery to the United States Army, from certain destruction after it was torn from its moorings during a violent storm.

Pricolo complained that Ilari, a former airshipman, had spent six years behind a desk neglecting the flying hours required to maintain his six-month pilot license, and forced him to comply.

On 30 December 1940 Ilari assumed command of the 4th Air Fleet, with headquarters in Bari, supporting operations in Albania during the Greco-Italian War and later the invasion of Yugoslavia.

On February 7, 1943, he chaired a meeting in which the details of a planned bombing raid on New York (Operation S) were discussed; it was established that the aircraft would tak off from Bordeaux and land in the Atlantic Ocean next to a submarine, which would deliver the fuel for the return flight.

[8][10][9] On 8 August 1943 Ilari returned to the command of the 3rd Air Fleet, headquartered in Rome, now tasked with opposing the Allied advance following the landings in Sicily and then in mainland Italy.

On 6 September 1943 the Minister of Aeronautics, Renato Sandalli, informed Ilari and the Deputy Chief of Staff, General Giuseppe Santoro, of the signing of the armistice of Cassibile, giving them the instructions on how to behave in view of the inevitable German reaction.

After the official proclamation of the armistice on 8 September 1943, Ilari entered into negotiations with Luftwaffe General Alfred Mahncke; on 12 September, after obtaining Sandalli's consent, an agreement was reached, stating that the air bases of the 3rd Air Fleet and their equipment and fuel would be handed over intact to the Germans, in exchange for the latter's commitment not to interfere with the safe departure of all Italian aircraft based there.