The reports on the flooding in the MRT tunnel seem to have largely put the blame on maintenance problems.

However, as transport correspondent Christopher Tan rightly pointed out, the problem originates from the "stop" switch that failed (SMRT, LTA have to get to root of the problem; Oct 17).

This stop switch is designed to stop the activation of the pumps when there is little or no water in the storm water sump pit.

The system is designed with a couple of redundancies, including three pumps and three float switches to start the pumps when the water level rises.

But the pumps failed to start because the malfunctioning stop switch had overidden the float switches.

This is a Design 101 flaw.

Can a good and robust maintenance regime overcome such a design flaw?

Predictive and preventive maintenance is good only if the impending failure of a component, or mean time between failures, can be established within a certain level of certainty.

Actions can then be taken to prevent the failure.

However, the system in question operates only intermittently, thus making the establishment of these parameters extremely difficult.

Moreover, based on the reports, the failure of the stop switch is likely due to the presence of sludge, which is not a normal mode of failure.

Thus, knowing the normal mean time to failure of this component will not help in establishing the right maintenance schedule.

A simple change in design would have alleviated all these maintenance issues.

There are tools to help to identify and eliminate these types of design flaws.

One of them is Failure Mode and Effect Analysis (FMEA), which identifies the failure modes, its effects, risk of occurrence and actions to be taken.

Performing FMEA can be quite a chore.

Therefore, employees may just go through the motions without attaching importance to it.

The problem may, hence, remain unidentified and the correct actions not taken.

If this happens, then it becomes a "cultural" issue that needs to be addressed.

If the wrong design philosophy is employed, just focusing on improving maintenance will not prevent similar breakdowns elsewhere.

A systematic review of the design may be appropriate, in addition to strengthening maintenance.

Chin Neep Hing