Finmeccanica's aeronautics businesses, including Alenia Aeronautica and Alenia Aermacchi, swung into loss for the nine months to end-September owing to a €753 million ($1.02 billion) charge against the Boeing 787 programme.
Alenia makes fuselage barrels in a purpose-built facility in southern Italy.
The reversal was also attributed to "a decline in industrial efficiency affected by difficulties experienced in certain productive processes".
Aeronautics revenue was flat at €1.87 billion as rising M-346 and ATR sales were offset by falling revenue from the Eurofighter and Boeing 787 programmes.
Separately, Italy's troubled state-dominated industrial group approved a restructuring plan that, in addition to setting its AnsaloBreda rail transport division on a sell-off course to "gradual deconsolidation", will see aeronautics businesses including Alenia Aeronautica and Alenia Aermacchi brought together into a single unit.
The aeronautics workforce will be cut in line with a union agreement reached earlier this month, and the plan also calls for "restructuring production and engineering activities, and streamlining the supply chain to reduce external costs."