This record speed was increased to 554 km/h (344 mph) when the modified prototype, using a double tail, was re-equipped with the definitive engines; the 746 kW (1,000 hp) Piaggio P.XI-RC40s. This time it broke German records in a 100 km (60 mi) stage at an average speed of 554.4 km/h/344.5 mph (with 1,000 kg/2,200 lb load) on 5 December 1937. Finally on 9 December 1937, another world record was set when averaging 524 km/h (326 mph) over 1,000 km (621 mi) with a 1,000 kg (2,200 lb) load.[3]