Software debugging is tedious and difficult process.
I am a programmer myself and have encountered several cases
of debugging mysteries, that took me weeks to solve.
My uncle worked many years for Litton, GE and NASA
as safety and quality control specialist.
(he is now retired, but still called in from time to time as a consultant)
He worked on Polaris, Delta but also Space Shuttle projects.
I asked him, is it true, that the core programme to run Space Shuttle
is still 128 kB big (no error - kilobytes).
His answer was affirmative.
He confirmed, that they checked by modelling and theoretical
calculations, that it is impossible to completely debug
(test the programme reaction to every and each input data combination)
by programme codes bigger than 128 kB.
The killer in this case is, that no redundancy can help in case when
on every of 5 computers sits the same software with the same bug.
Hence Space Shuttle files with a software smaller than that of
your modern washing machine.
I don't know what is the size of the RR FADEC system, but if it's
bigger than that of Space Shuttle, it will never be properly debugged.
