Blocking the interlocks

Perhaps. I think it was you who referred to it as "blocking the interlocks".

That brings back memories ('twas my first post over there).

Sometimes during failures you may get the scenario that a route hasn't normalised for whatever reason.

Whilst an emergency release facility is available in every IMR (though not always on every signal) it will only get you out of trouble if the signal is approach locked or if the back end protection (i.e. route releasing delta circuit or timer) has failed. It is of no use if the failure is associated with the through route protection of the lock circuit. It is in this scenario that the lever must be manually restored to normal, known as making an 'irregular adjustment to the signalling'.

The simple procedure is:
1. All trains in area to be stationary at red signals.
2. All auto route setting (Programme Machine, Computer etc) cancelled
3. All route calls cancelled
4. Air off lever frame
5. Route which is to be released physically checked to be clear of trains
6. With assistance of a second competent person (T/O or higher, but more usually an Operating Offical) you perform the release.
7. The T/O will lift the failing lock by hand. When it is lifted the second person moves the lever normal, and the air is put back on, control handed back to the signal op etc.

On the Central, East London and parts of the Jubilee a slightly different method is used to give the release (as there are no locks to lift), but the principle is the same. They are the only rooms which have a facility provided to perform such an irregular adjustment, on all conventional lines it is done manually.

I think we had best keep the full story to ourselves - the procedure as I mentioned it is from my Tech 2 notes.

Thanks for the information - I was always curious about that aspect of fixing a failure.