The fall ‘would have been almost impossible to survive’, John Stevenson, leader of the Lochaber Mountain Rescue Team said today.
It is believed the climber’s rope might have ripped after snagging on a sharp edge.
His climbing partner, in his 30s, was rescued uninjured from a ledge after raising the alarm at around 6pm. Both men were from the east of Scotland, it is believed.
Mr Stevenson said the fatally injured climber had been leading the expedition.
He said: ‘He had fallen around 400 metres (1312 feet) and sadly struck a lot of rock on the way.
‘He was climbing with a friend. They were roped together and it is not clear at this stage what has happened.
‘But one possibility is that the man who fell – who was leading the climb – lost his hold.
‘The rope that was holding him then snagged on a sharp edge and was cut as a result. He then had a big fall which would have been almost impossible to survive.’
Mr Stevenson said the man, who has not been named, was found by four rescue workers at the bottom of the climb.
More than 30 ‘courageous’ rescuers took part in the operation, including 13 from the RAF Mountain Rescue Team who were on their way to a weekend training exercise.
Mr Stevenson continued: ‘His friend was stuck, sat on the ledge, about 150 metres (492 feet) below the summit. He was still tied to the rock face.
‘By the time we got him it was dark and we had to find a line into him. The boys did a good job in very demanding and difficult circumstances.’
He added: ‘Everybody did a great job, including the helicopter crew, and the climber on the ledge, who was in his 30s, was a bit cold but otherwise fine.
‘Obviously the enormity of what has happened will sink in over time. He just saw his friend fall and keep falling.’
Police Scotland said emergency services were alerted to the incident by the man’s climbing companion.
The Coastguard search and rescue helicopter from Inverness airlifted the men from the hill around 2am.
A spokesman said: ‘Sadly the casualty, who was in his fifties and from out with the area, died as a result of his injuries. Officers are liaising with next of kin.
‘Members of the mountain rescue teams are thanked for their courageous efforts during the rescue, carried out in dark and difficult conditions.