David Goodhew, assistant chief officer of Scottish Fire and Rescue Service, described it as "extremely difficult and complex" work as they battled to search the premises for bodies while ensuring the building did not collapse.
Some victims' relatives have criticised the speed of the rescue operation. Ian O'Prey, whose son Mark has not been seen since the helicopter came down on the bar on Friday night, said he believed the recovery of the helicopter had taken precedence over removing bodies.
"I feel it could have been done better," he said. "Communication was dreadful. I'm sure they could have got the bodies out quicker."
Mr Goodhew said: "Part of the reason it has been so difficult for emergency services to undertake the rescue is that this particular premises used to be a tenemented building.
"It was three or four storeys high, so actually the walls you see are not nine inches thick, they are almost a metre thick at the bottom."
Mr Goodhew said that to attempt to remove the front wall of the pub would have caused the further collapse of the building on to casualties inside.
"The quantity of rubble was far greater than a normal roof and it was substantial in every area you looked at," he said.
Thermal imaging cameras, timber supports and hydraulic rescue gear were used. Firefighters trained in urban search and rescue - first developed during the Second World War to deal with bombed out structures in the blitz and also used following the 9/11 attacks - were key to the work.
Mr Goodhew said: "Heavy rescue equipment was brought in to lift the helicopter, which weighs approximately three tonnes. Our approach was to lift it from its current location without causing any further damage to the structure of the aircraft. That will assist with the ongoing investigation being carried out by AAIB.
"Struts and strapping were used to secure the fuselage to allow the helicopter to be lifted safely. It had already been lifted by approximately two feet to allow it to be secured and made ready for extraction. This has been a very delicate operation and we have had to take great care not to disturb the scene.
"We have also been extremely mindful of the very sensitive circumstances of the situation in which members of the public and Police Scotland lost their lives."