On 6 Feb, 10:26, wrote:
The central line is ATO, I assumed the remaining signals were just an
emergency backup system. What does it matter if one of them fails and
why would it mess up the service?

"Signal failure" is a generic term they use for a failure of the
signalling system, and only occasionally means a failure of an actual
signal.

(The Central Line still has a relatively conventional signalling
system, it's just conveyed to the train through the track rather than
to the driver through coloured lights)

U