SINGAPORE - Lift company Sigma Elevators is still banned from tendering for new projects, said HDB, as its performance has yet to meet the required standards.

The update comes nearly a year after the Housing Board revealed it had forbidden Sigma from bidding for new projects since October 2015.

This is so that the firm - a subsidiary of American company Otis Elevator Company belonging to the United Technologies group - can "focus on improving the installed lifts under their current contract".

Noting "some observed improvements in the performance of these lifts", the spokesman told the Straits Times: "We are closely monitoring the progress of the improvement works, and will review their status after they have fully met our lift performance and service standards."

There are around 3,500 lifts built by Sigma out of about 24,000 lifts in HDB estates here. In 2013, HDB awarded a tender to the company to install 469 lifts in new flats. But the company, unable to meet deadlines, was not allowed to tender for new projects in 2015.

In 2016, HDB noticed a higher-than-usual breakdown rate in the lifts installed by Sigma in their first year of operation. An investigation found that the doors and sensors were more prone to misalignment, possibly due to knocks from rough usage from renovation and home moving activities.

Accumulated debris in the door sills, which are metal rails along which the elevator doors slide, could also cause the elevator to stop working, a Sigma spokesman told ST previously.

This occurred mainly in lifts in their first year of operation, in newly completed flats under the 2013 tender.

The company has said it has worked closely with the Town Councils and HDB to rectify the issues, with HDB adding in its latest reply that improvements were seen where Sigma has "undertaken rectification works for this batch of lifts progressively".

But there have been recurring problems for Sigma-branded lifts which are not part of the 2013 tender as well.

In five public estates tracked by ST - Punggol Arcadia, Edgefield Walk, Waterway Cascadia, Natura Loft and McNair Towers, the Sigma lifts there still break down repeatedly and are out of service for long periods.

Three of these - Punggol Arcadia, Edgefield Walk and Natura Loft - are about five to seven years old and the lifts there are not supplied under HDB's lift term contracts, but through each development's contractor.

Said HDB of these estates: "The respective Town Councils had engaged Sigma, the lift contractor, to maintain the lifts. We will work with the Town Councils and Sigma to improve the performance of these lifts through regular checks and maintenance."

In August, the Ministry of National Development revealed national lift breakdown figures for 2013/14 and 2015/16 in public housing estates, showing things had improved. On average, there were 20 lift breakdowns per 1,000 lifts a month in 2015 and 2016, down from around 30 in 2013 and 2014.

But not all residents have seen improvements.

At Punggol Arcadia, one resident, who started compiling an Excel sheet of "Lift Reports" from June, recorded a surge of nearly 50 lift breakdowns in September alone, up from 15 in the previous month. The last reported incident, according to the resident, was on Nov 8. However, his data did not distinguish between whether each incident was case of lift breakdown or that the lift was put out of service because of maintenance.

At Bishan's Natura Loft, a Design, Build and Sell Scheme estate, the breakdown of the high-speed Sigma lifts in the estate's three 40-storey blocks has continued to inconvenience residents.

In one incident on Aug 5, nine people were trapped in a Natura Loft lift for more than an hour when it stopped between two levels. A Sigma technician arrived late as he was stuck in traffic, ST understands.

So exhausted were the nine - who included elderly residents and infants - that three seniors had to be placed on drip. Other residents passed food and drinks through the gap.

The lift was eventually opened manually by a technician and there were no reported injuries, said the Singapore Civil Defence Force.

But the incident is still on the minds of residents months later, they told ST.

When oral exams for the Primary School Leaving Examination were held later in August, a Sigma technician was put on standby at the foot of the blocks to assuage the worries of parents.

Said resident Jonathan Ho, 37: "Here's the crux of it - When the foundation is weak and you start with a bad set of lifts, you will forever be playing the game of catch up and repair.

"They have to decide whether it is worth more to start from a point of solidly constructed lifts or to continuously maintain a poorly made one."

The Bishan-Toa Payoh Town Council declined to comment.