Dr Lachmann, who was 10 metres ahead of his partner when she suddenly disappeared, managed to treat her and secure her as best he could before trekking 2.5km over steep ice terrain to raise the alarm.
For the South Westland ACR team, the steep, perilous terrain and poor visibility posed an enormous challenge.
After flying to a nearby point, the team were forced to make a life-or-death decision - try to reach the trapped climber despite the conditions, or leave Ms Hellenbrandt trapped overnight, with poor chances of survival.
Mr Innes then said he could drop the team on a high, exposed razorback ridge above Glacier Peak, but they'd have to stay overnight.
"It was a risk we were willing to take, and once we'd made that decision, I suppose it made everything easier," he told the Herald.
What followed was several minutes of the most intense flying of his career.
In white-out conditions, he had to crawl the chopper under cloud on the eastern side of the ridge, before dropping down on to the ridgeline, one skid touching the ground.
"I had to hold the helicopter extremely still as they got out, as I didn't want to knock them off the hill - looking down between my legs, it was a long, long way down ... maybe 4000 or 5000 feet."
Mr Innes then had to rotate the helicopter for the rescue team to off-load equipment from the other side.
With cloud now having thickened to reduce visibility to just one metre, the team began searching the glacier, calling out for Ms Hellenbrandt.
Mr Innes was waiting with the Mt Cook LANDSAR team in a nearby hut when Mr Bron radioed through that they had established voice contact.
"That was quite an emotional moment," he said.
"To be honest, we all had a pretty negative outlook on how it was going to end up for her ... we were pretty sure, from what Helmut had described, that she would have been deceased by the time the guys arrived."
The team kept close to her overnight, managing her hypothermia and keeping her talking, until they safely flew her out the next morning.
To this day, Mr Innes still feels good when he thinks about the mission.
"The overall thing that made it very memorable was that under quite challenging circumstances, we had a good outcome - and those, you don't always get."
South Westland Alpine Cliff Rescue team leader Marius Bron with Sabine Hellenbrandt, during the rescue on Explorer Glacier:
