6 September 'Partial failure of the tripcock' is identified as emergency brakes fail to activate when a train passes a red light. The tripcock is a lever on the train's leading wheel which on hitting a track mounted 'train stop' lever should activate emergency brakes.
Similar failures occur on three subsequent re-enactments.
7 October Tube Lines staff take control of Alstom depot to investigate the faulty brakes.
LUL steps in to supervise work, exercising an 'emergency direction' role under the PPP.
10 October Fault is put down to the reset mechanism - a length of rope - for the tripcock on the trains after one was found to be frayed and snagging.
10-12 October The ropes are replaced with new, smaller diameter ropes.
12 October Tripcock fails again in testing.
13 October Drivers refuse to operate Northern Line trains on safety grounds.
13-14 October Further investigations reveal low hydraulic pressure in the emergency brakes to be real cause of failures.
15-17 October Pressure is adjusted and 1,028 tests carried out to check system is safe.
17 October Trains back in service.