Three engineers from the Defence Science and Technology Agency (DSTA) helped solve the mysterious glitch which affected the MRT Circle Line in recent weeks.

This was revealed by Defence Minister Ng Eng Hen on Facebook yesterday.

Together with a Defence Science Organisation (DSO) team led by Mr Chian Teck Keong, the three - Mr Mui Whye Kee, Mr Cheng Heng Ngom and Mr Benedict Koh - pinpointeda train with faulty signalling hardware as the cause of the glitch which affected service from Aug 28 to Sept 2 and from Nov 2 to 6.

Mr Mui and Mr Cheng are prize-winning engineers who have won the prestigious Defence Technology Prize.

Mr Ng said in his Facebook post: "In modern battles, the opponent who rules the airwaves has the decisive advantage. We have many professionals in DSTA and DSO National Laboratories who spend a good part of their careers becoming experts in the field. So, when the Circle Line had problems with signal interference, it presented an opportunity for them to help and put their expertise to good use."

The minister added: "Like good detectives, they analysed the clues, eliminated other suspects and caught the culprit - train PV46, carrying faulty hardware."

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There were many theories to explain the glitch, from a recent software upgrade and telecommunication signal interference to sabotage.

The signal interference first appeared on Aug 28 and persisted until Sept 2, when it ceased as suddenly as it started. Over those six days, rail operator SMRT, suspecting a new software, rolled back the update, but the glitch continued.

Telecommunication signals were switched off along certain stretches of the line, but before any finding could be made, the glitch stopped.

It then reappeared on Nov 2, causing a serious service disruption in the morning peak hour. This time, the operator and the Land Transport Authority (LTA) sought a total shutdown of telecommunication services along the entire line. The glitch did not go away.

The Straits Times understands that the DSTA took one weekend to crack the case.

National University of Singapore transport researcher Lee Der-Horng said: "It is a relief to know the cause has been identified. However, it also makes us wonder if our train operators and LTA have the required expertise in troubleshooting faults.

"Moreover, the quality control procedures before the train was delivered may need to be tightened."

Sales manager Ashley Wu, 35, who uses the Circle Line, said her confidence in the line has not been affected, although commuting without phone access "was very boring".

"But I'd be very worried if it happens again," she said. "I would then lose my confidence, I think."