But surely there's some else clause at the end with a default value, no? Or at the minimum log.error("No matching flight conditions configured", pressureAir, pressureFuel, airspeedMach, engineRPM) or such?
Yes of course there is fault handling! That's one of the hard things about safety critical sw is that you actually have to deal with everything.. Lettings things "fail" or be "undefined" isn't really an option.
E.g. Mach is derived from multiple sensors so you have a first layer of redundancy there, then if all fails (and you can detect it ofc..) you'd probably start some kind of dead-reckoning and issue WARNINGS accordingly to the pilot and/or connected systems that change its behavior to a more conservative one.
There is almost always some kind of "safe state" that wouldn't depend on the input signals at all. It would obviously negatively affect the performance of the aircraft and most likely reduce its operational envelope.
Pilot action would be required, i.e. reduce altitude, reduce AoA, reduce air speed etc. LAND ASAP etc. :)
