Metro Door Indication Fault at Peak Headway
A six-car metro train on a 3-minute peak headway reports door 3 on car 4 failing to close at three consecutive stations. The driver resets the door; it closes, but the 'door closed and locked' indication flickers. At the depot, a repeat test shows an intermittent limit switch. There is no spare switch in the depot store, and the next peak service is due in eight minutes. Twenty-two trains are in service, each carrying about 1,200 passengers; platform screen doors are fitted throughout. A spare train is available but needs 12 minutes to prepare and will miss two peak paths. The maintenance manual requires positive door indication before dispatch, but a supervisor suggests locking out the door and running with five cars' doors active. The failure has occurred twice on this train in two days.
1. Should the supervisor's proposal to lock out the door and run be accepted? Justify.
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No. The indication is not positive, and the fault is intermittent; locking out the door removes the safety function and leaves a door that may open or fail to close with about 1,200 passengers on board. The maintenance manual requires positive door closed and locked indication, and the repeated failures in two days show this is not a one-off glitch. Running with five cars' doors active does not cure the fault and may mask a wiring or connector problem affecting other doors. The correct action is to withdraw the train at the next terminal or depot, insert the spare train, and accept the two-path hit. A 3-minute headway can absorb one train if the spare is inserted promptly; a door incident is far more serious. The supervisor's proposal is an operational convenience, not a safety case.
2. What immediate checks and root-cause actions would you order?
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Isolate the door circuit and inspect the limit switch, wiring loom, connector pins, striker alignment and door track. Intermittent behaviour after rain or cleaning often points to moisture ingress or a loose connector. Swap in a known-good switch for test only, not for passenger service, and perform at least 20 open/close cycles with a tap/vibration test. Compare the physical switch state with the indication in the train computer. Review the two earlier failures to see whether the same door and car are involved. If no spare switch is available, keep the train out; cannibalise from a withdrawn train only with traceability and a functional test. Do not adjust the switch merely to force a positive indication. Log the root cause and check the batch.
3. What passenger and service controls would you apply, and what would you report?
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Withdraw the train at the next depot or terminal, insert the spare, and publish a 2–3 minute delay. Station staff should manage platform crowding because platform screen doors are fitted and a stalled train blocks the platform. Do not leave the defective train in passenger service or lock out the door. Report the incident number, door and car, the three station failures, the indication flicker, the depot test result, the action taken, and the root cause as pending. Notify the rolling stock engineer and operations control, and record the supervisor's request and its refusal. Set a repeat-fault threshold: any recurrence after repair triggers a fleet check of the same switch batch. If the spare is not ready in 12 minutes, temporarily increase headway rather than dispatch the defective train.