Michael Bonner said he rushed to the scene after Basilio Brazao, 19, plunged down the shaft at Earlsburn wind farm near Fintry, Stirlingshire.
Mr Brazao, of Dunbar, East Lothian, was wearing a safety harness but no helmet when the accident happened.
He said the teenager was wearing a harness that he thought was clipped on to a ladder in the turbine.
The court heard a statement that Mr Bonner had given to Health and Safety Executive investigators shortly after the incident on May 22, 2007 in which he said: "I could see the guy had a harness on but I'm not sure if he had a hard hat. I don't recall his harness being clipped on to anything."
Questioned by Depute Fiscal Gavin Callaghan about his recollections, he said: "During the last seven years I've been thinking constantly about the boy. "
The inquiry heard that the cause of Mr Brazao's death was multiple injuries and blunt force trauma.
At the time of the accident he was working for Turbine Erection Cabling Services, subcontracted by turbine manufacturer Nordex UK.
Nordex was employed by a subsidiary of Falck Renewables which was developing the 15 turbine windfarm.
In 2012 Nordex was fined £26,000 at Stirling Sheriff Court after admitting health and safety breaches, but the prosecution said Mr Brasao's death was not caused by or connected to the breaches.