250 kts:
Why all the demands to get other people to check these training boxes?
I'm sure that I can't be the only person who ALWAYS does a test transmission on his training box as soon as he sits down with a trainee. This is good practice and has identified a problem with the 'black box' to me on at least one occasion in the past. If it then doesn't work, you take it to the engineers who return it with a little 'servicable' label on it. That's their guarantee to us and them taking their share of responsibility.
Seems to me from this incident that the problem with inter-sector cordination is making itself apparent not only between LACC & LTCC but also now internally at Swanwick. Having also had personal experience of this sort of failure recently, I'd be more worried about that as you are less able to mitigate against it with simple checks.
Regards
Sad.