They put on orange overalls, buckles and ropes, signed a couple of disclaimers and off they went. Call them courageous, foolhardy or stark raving mad, so far this plucky trio has brought in more than $500,000 - and rising - for the campaign.

After heading up 60 floors in a lift, the trio - Mr Slevin; Quek Kwang Meng, head of real estate investment, Asia Pacific; and Kevin Rasmussen, manager and foreign exchange counsellor, investment - walked out onto the balcony for their final instructions. Before the gate opened, they had their last chance to opt out. Then they were plummeting towards the ground at 75km/h.

'It's just that final moment,' said a relaxed Mr Slevin after the jump. 'The instructor said 'don't look down', and then he said 'move your feet forward', so of course you look down at your feet and it's a long way down.'

'It was the final preparation that was scary,' said Mr Rasmussen, 26. 'After that, it's just an adrenaline rush all the way down. When you look down, all the cars look like toys. But I'm so impressed with the half a million. That's staff donations and support from all our regional offices, including Singapore. And it's for such a good cause as well.'

Citigroup, which supports many other charitable causes during the year, is joining Operation Santa Claus for the first time.

'The staff have been fabulous,' said Mr Slevin. 'It was put together at relatively short notice and over $200,000 was pledged by staff on the first day. If you look at the breadth of charities in Operation Santa Claus and the causes that are being supported, we felt we ought to be supporting that.'

Mr Rasmussen, a US citizen, was in the US army for six years. 'I've jumped out of a plane before, but I felt this was more frightening than parachuting because the plane just opens at the back end and you have no sense of the height you're at. With this, you can look all the way down and you're just dependent on a cable that's suspending your life.'

Before the jump, Mr Rasmussen was provided with a special string for his sunglasses. 'The sunglasses don't come off,' he said. 'They're part of my head.'

His girlfriend, Flora Siu Lok-sze, looked on nervously from down below as her boyfriend made his descent to terra firma.

'At first I felt very scared. Actually, I was more scared than him. But now I support him,' she said.

'I convinced her with stats and freefall speed statistics,' Mr Rasmussen said afterwards. 'It's safer to do this than sit for eight hours in the office with your legs crossed.'

Matthew Quek, 12, who accompanied his father, said he was proud of his dad.

Would the three men do it again? 'Yes, definitely!'