I placed a Super Locomotive to test some things, and got a rather unpleasant surprise.
The mod Train Control Signals (1.0.4) caused a non-recoverable error.
Please report this error to the mod author.
Error while running event Train_Control_Signals::on_train_changed_state (ID 24)
__Train_Control_Signals__/script/train_control_signals.lua:16: attempt to index local 'fuel_inventory' (a nil value)
stack traceback:
__Train_Control_Signals__/script/train_control_signals.lua:16: in function 'train_needs_refueling'
__Train_Control_Signals__/script/train_control_signals.lua:99: in function 'handler'
__core__/lualib/event_handler.lua:47: in function <__core__/lualib/event_handler.lua:45>
It would seem TCS does not check that the train indeed has a fuel_inventory
that is indexable.