Boom production models will use COTS avionics just like every other business jet manufacturer. They'll have to write custom flight control software but that will be much easier than on a military aircraft. No weapons, no external stores, no defensive systems, no tactical data link, no complex navigation modes, etc.
Except they'll need to write that flight control software themselves, for a plane so different from modern aircraft that there are literally no experts in software design for this class of aircraft. (Outside of anyone doing it for the military, and I can't imagine they'd be allowed to repurpose that work.) There will need to be a whole lot of new software development, along with the corresponding review process by the FAA. Simpler than a complex military fighter, but there's no COTS solution for the software and that's a huge part of this project.
Looking at the current state of open source software like ardupilot, and the fact that we've had supersonic jet fighters since the 1950s (F-100 Super Sabre) I don't think the control software is going to be a major bottleneck. If anything, not being tied to legacy control software may improve their velocity and testing. Navigation solutions should be drop in. Garmin, etc offer drop-in glass cockpit retrofit solutions for Cesnas from the 1960s.
If Boeing can't make the Max work without crashes, what makes you think a completely new supersonic aircraft can use a fork of Ardupilot with a few minor extras for supersonic flight?
Supersonic flight has much less overlap with subsonic flight than you might think. There are compression and twisting forces on the fuselage and flight surfaces which have no analog in conventional airliners.
And you can't just take the flight characteristics of one shape/size of aircraft and tweak them a little for your new design.
'If X can't do it...' is a bad argument that doesn't take any consideration of real life.
Just because they are a huge company with big spending power does not make it impossible for their codebases to be a pile of hot steaming garbage that even the best engineers struggle with.
Either way, your rebuttal about Boeing doesn't address the fundamental differences between control of a traditional aircraft-- which is all that any existing software can handle-- and control of a fundamentally different type of aircraft.
> Supersonic flight has much less overlap with subsonic flight than you might think.
And every supersonic aircraft also has to fly subsonic. So you really need two sets of software in a supersonic aircraft. Or more accurately three, because the transonic regime is weird enough to be its own thing.
What about the airplane given in the original example, the F-100, whose design predated the integrated circuit by something like a decade? Presumably control software improves stability, but otherwise the aircraft behaves in a predictable manner above and below Mach 1 as supersonic control software is a relatively recent addition.
Stuff in civilian aviation is designed to be certified before its flown commercially, stuff in military aviation is designed to be adapted on an evolving battlefield.
