Heavy landings on the ground floor, lifts stopping mid-journey and buttons turning off after being pressed.
Such erratic lift behaviour and at least 20 breakdowns this year have plagued residents of the new Build-To-Order premium flats at McNair Towers in Boon Keng since the keys were handed over in August last year.
There are four blocks at McNair Towers, with Blocks A and B having 35 storeys, and C and D, 28 storeys.
Sales adviser Eileen Long, 30, and her family of four had a bad experience with one of the three lifts serving Block B on Oct 18.
"There was a very loud sound when it landed on the ground floor with impact. Thankfully, we were not hurt, but my daughter was a bit traumatised."
Ms Long was with her husband and two children, aged one and three. A day after the incident, the lift was shut down for two days for maintenance work.
Mr Howie Hau, 50, a financial trader, said he was in a lift in Block A in August when it jerked, stopped and went into free fall for a short while.
There was a very loud sound when it landed on the ground floor with impact. Thankfully, we were not hurt, but my daughter was a bit traumatised.
SALES ADVISER EILEEN LONG, on her experience in a McNair Towers lift.
I think the most important issue is safety, because if a lift jerks suddenly, elderly people might fall or get a shock.
ENGINEERING ASSISTANT YUEN WAI FANG, who lives at McNair Towers but has not experienced a lift breakdown.
"It does not seem safe for the lift to be free-falling, even if it is just for a few floors. Now, we try to avoid that lift whenever we can because it seems to be the most problematic," he said.
He said there has been a lift breakdown almost every week since he moved in April.
Lift doors and sensors of these lifts, which were installed by Sigma, were more prone to misalignment from heavy and rough usage, especially during the lifts' first year of operation due to renovation and moving activities, a Housing Board investigation showed.
In response, HDB has instructed the lift manufacturer - Sigma Elevator - to carry out servicing twice a month, instead of once, as is normally done, and progressively carry out improvement works to raise lift reliability.
Its spokesman said: "While there has been an observed increase in reported lift issues in September and early October, Sigma has been carrying out additional checks and rectification works, and the situation has since improved."
Jalan Besar Town Council, which the blocks come under, confirmed that it has been conducting regular inspections with Sigma.
"At our request, Sigma has specially allocated a team to monitor and look into the lift issues at these blocks," said the town council.
Besides improvement works, HDB said measures have been taken to encourage proper use of the lifts, such as through educational posters and YouTube videos.
When asked about the possible causes for the repeated breakdowns, Sigma Singapore general manager Adreana Goh said: "An internal investigation found that the vast majority of riders' feedback was related to issues with the operation of lift doors."
She added that the project was awarded to Sigma in March 2013.
Ms Yuen Wai Fang, 41, an engineering assistant who lives with three other family members in Block D, has not experienced a lift breakdown, but said: "I think the most important issue is safety, because if a lift jerks suddenly, elderly people might fall or get a shock."