This was not the limit of the Bone Wings, but the limit of Brian's body.
The faster the speed, the greater the pressure his body faced.
Although Brian's physique improved in all aspects each time, his body had its strong and weak areas, and its strength was not constant. He did not possess the ability to protect his body with Inner Qi, relying solely on his flesh to withstand the forces.
Therefore, unless he transformed his body into a conical, streamlined curve, a speed of three Mach, equivalently 2448 kilometers per hour, was the maximum safety flying speed for Brian.
By transforming into a conical streamlined curve and ignoring injuries, burning up stored Gift Energy, he could push this speed up to three Mach.
That was an exaggerated figure.
Three Mach meant a speed of 3672 kilometers per hour!
Most fighter jets did not reach that speed!
Crucially, Brian's overall body size was not large, so typical sounding radars would not detect him.
