The A109 is powered by two Pratt & Whitney 206C engines, housed in independent fire-proof bays and controlled by Full Authority Digital Engine Control Units. The twin-engine design gives the pilot more flexibility when planning routes over built-up areas, as the aircraft can operate at limited weights on a single engine; therefore even if power from one engine is lost, the aircraft can maintain height to clear the built-up area. The twin-engine design also increases safety margins when flying in and out of confined landing sites.
The aircraft is a twin-engined, eight-seat helicopter with retractable undercarriage, weighing about 2000 kgs and cleared to operate up to 3000 kgs. The rotor system comprises three main rotor blades and two tail rotor blades of composite construction. The A109 has two independent hydraulic circuits, driven from the main rotor gearbox: one provides power to one side of the main servo jacks and gives servo assistance to the tail rotor, while the other services the other side of the main jacks and powers the utility services for undercarriage movement and braking.
Until 2008, when they were replaced by the Dauphins, 8 Flight operated a fleet of 4 Agusta A109s, two of which were captured from the Argentines during the Falklands conflict. 8 Flight is based at SAS HQ at Credenhill, near Hereford.
Currently on lease with 660 Squadron based at RAF Shawbury are two Augusta 109E's for pilot training.