How fast can a jet aircraft go?

Answer 1

1. conventional jet engines (using a compressor) will operate at speeds up to slightly less than Mach 1
2. using an afterburner a conventional jet engine can operate at speeds slightly above Mach 3
3. ramjet engines will operate at speeds up to about Mach 5
4. scramjet engines can operate at speeds well above Mach 6

However the maximum speed of of an actual airplane is usually less than the capability of the engines it uses.