RL-201 first flew on 25 March 1958 with Chief Development Test Pilot S/L Janusz Żurakowski at the controls. Four more J75-powered Mk 1s were delivered in the next 18 months. The test flights, limited to "proof-of-concept" and assessing flight characteristics, revealed no serious design faults. The CF-105 demonstrated excellent handling throughout the flight envelope, in large part due to the natural qualities of the delta-wing, but responsibility can also be attributed to the Arrow's Stability Augmentation System. The aircraft went supersonic on its third flight and, on the seventh, broke at while climbing. A top speed of Mach 1.98 was achieved, and this was not at the limits of its performance. An Avro report made public in 2015 clarifies that during the highest speed flight, the Arrow reached Mach 1.90 in steady level flight, and an indicated Mach number of 1.95 was recorded in a dive. Estimates up to Mach 1.98 likely originated from an attempt to compensate for lag error, which was expected in diving flight.