As designed, the traction interlock automatically deactivated after a period of time. This allowed traction to be applied and the train to depart with the carriage doors open.
ATSB accepts MTM’s proposed actions on this safety recommendation.
The ATSB recommends that MTM considers a modification of the traction interlock override system to incorporate additional risk mitigations.
ATSB accepts MTM's proposed actions to this safety recommendation.
MTM agrees with the recommendation that it consider a modification of the traction interlock override system, in the terms suggested. It has done so.
MTM has now completed a risk review of the traction interlock timing. It is considering proposals to modify the interlock override system on both X’Trapolis and Comeng Fleets which have the same functional design.
Proposed changes following this risk review
The proposed steps are to undertake circuit modifications and install a key operated override switch. When implemented, these measures will allow a train to gain traction control in circumstances where a door appears to be open, but will differ from the arrangement at the time of the incident in that they require an additional manual intervention from the driver.
Circuit modification
Circuit modifications will necessitate the removal of the existing timer relay circuit that provides for the functionality to be restored after a 60 second delay. Therefore if a ‘door open’ condition is detected following the initiation of the ‘door close’ command, the circuit will inhibit traction without time limitation, until the key switch is operated to reinstate traction.
Key switch
The key switch will allow a train to obtain traction (whether in the usual running of passenger services, or otherwise by the manual intervention of a person authorised to have a copy of the key. The functionality will be such that once operated to regain traction control, it will be mechanically locked in that position and remain so until reversed to the normal train operating status.
During the running of a train, MTM’s systems will be such that the key can only be operated by a driver properly authorised and having the appropriate operating key. It should be noted that this is a similar configuration currently on the Siemens fleet.
Proposed implementation period
For Comeng trains within the MTM fleet, the installation of the proposed solution is being undertaken as part of the Comeng Life Extension program and is planned to commence by December 2016.
For X’Trapolis trains, the implementation works are scheduled to commence after circuit validation by the train designer ALSTOM. For a number of reasons, MTM cannot proceed to make these alterations without ALSTOM approval.
In discussion with DEDJTR (Department of Economic Development, Jobs, Transport and Resources), the body with overall funding responsibility for the Melbourne metropolitan train network, it is proposed that new X’Trapolis trains being ordered would be the first fitted, with changes to other X’Trapolis trains being the subject of further review of funding options and availability.
MTM confirmed that the circuit modifications had been implemented across the fleet.
The ATSB accepts MTM's proposed actions on this safety recommendation.
