Action today by Piccadilly line drivers has forced management to ensure the safety of the fleet.
Drivers have been telling the line's management for ages that there is a problem with the brakes. But while LUL was denying it - preferring instead to blame 'driver incompetence' - Tube Lines decided that a mechanical change was needed (implying that there had been a fault after all). Unfortunately, the technical fix made matters worse not better, as the new microswitches did not work properly and interfered with the downloads!
Fleet maintainers and drivers were rightly concerned that the trains were no longer safe, and so drivers, quite rightly, took matters into their own hands and refused to drive them. What months of talking would not have achieved, decisive action did achieve - with management committing to double-checking every train before it goes into service.
We can only guess what might have happened had the drivers not taken this action.