In the UK, it is not strictly legal, but it is not actually illegal either. This practice has been used on rare occasions but it is not standard practise. General consensus is that it is not recommended. There are other ways such as a tandem lift which would be seen to be a better option or using a system such as a Mega lift.

Phil I hope you can find it in the Iso mentioned by Rob. If my memory servers me correctly if you use 1 Crane 2 hooks there is a second where the lift is not recorded on the computor as you change to the lifting hook.(This might now not be the case) Yes this method was discussed in the erection of wind turbines we as a company would only use 2 cranes on a tandem lift because of the computor anomaly. I have not been involved in Wind turbine erection for about 7 years so I will try to find out what method is now used.