A HEALTH & Safety Executive (HSE) probe has failed to find the cause of the Canary Wharf crane accident in 2000, according to a report published this week.
Three men died after crane's top section overturned and fell 120m during the construction of bank HSBC's 44-storey office block.
The three Hewden Tower Cranes employees killed were using Wolff hydraulic climbing gear to add new mast sections to the crane.
The gear wrapped around the tower frame and was used to jack up the crane cab while new sections were slotted into place underneath it.
Guide wheels attached to the lower part of the frame allowed the climbing frame to move up and down the tower.
The HSE report says the operation to increase the crane's height was at its riskiest when the accident occurred.
Investigators concluded that abnormally high loads on one set of guide wheels triggered the collapse, caused by 'an unusual combination of factors'.
But, the report rules out excessive wind as a reason and deems a structural defect unlikely to have caused the crane to overturn.
It also considered hydraulic failure, the slewing of the crane and balancing errors to be improbable causes.
Hewden Tower Cranes workers frequently clocked up 80 hours a week, but investigators judged that there was insufficient evidence to put fatigue forward as a cause.
HSE recommended no criminal charges be brought and has established new training courses for tower crane erectors.