As refinements in the A340's design proceeded, a radical new engine option was offered by International Aero Engines, a group comprising Rolls-Royce, Pratt & Whitney, Japanese Aero Engines Corporation, Fiat and MTU Aero Engines (MTU). The engine nacelles of the superfan engine consisted of provisions to allow a large fan near the rear of the engine. As a result of the superfan cancellation by IAE, the CFM56-5C4 was used as the sole engine choice instead of there being an alternate option as originally envisioned. The longer-range versions, namely the A340-500 and -600, are powered by Rolls-Royce Trent 500 engines.