A route has been chosen on an overhanging cliff which two climbers will attempt to ascend within six hours - live on television.
Dave MacLeod and Tim Emmett will tackle Sron Ulladale on Harris on 28 August.
Lochaber-based Mr MacLeod said the route offered a continuous climb that should keep viewers gripped.
But he added the second pitch on the climb up the rock face was hazardous and could threaten the success of the project.
Mr MacLeod told the BBC Scotland news website: "That second pitch is likely to be the hardest part of the whole climb. It is really, really difficult.
"If I fall from there I would have to go back to the start of that pitch and do it again.
"But because of how difficult it is, I might not have the strength to try it again and put the whole climb in jeopardy."
After two to three weeks at the cliff searching for a suitable new route, Mr MacLeod said he had learned how the weather could affect the attempt.
Because of the overhang, the route was sheltered from the rain.
The wind, however, could cause problems for the climbers and the film crew.
Mr MacLeod said: "Wind is a potential problem on the day.
"The cliff is not a smooth surface and there are lots of sharp edges which is not good if you are swinging around in the wind on a rope.
"A bigger problem for the camera team is the cold. They will be freezing staying in the same spot for several hours."
In the final countdown to the live climb, Mr MacLeod will continue training and prepare diagrams of the cliff as a guide to the camera crew.
He said the team faced as enormous a challenge as himself and Mr Emmett would have, trying to film from the cliff face, along with battling any bad weather to transmit the footage via satellite.
The live climb will be filmed in high definition (HD) and broadcast on BBC Two Scotland and on the BBC HD Channel.
Triple Echo - which produces BBC Scotland's Adventure Show - said the Sron Ulladale climb would be a world first in terms of the technology used during the outside broadcast.
Mr Emmett is an extreme sports athlete and climber. He is also a motivational speaker.
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