Bond Offshore Helicopters has admitted proper procedures were not followed when problems first emerged with the AS332-L2 on March 25, a few days before the crash.
A magnetic particle was uncovered on the epicyclic chip detector component of the gearbox that day. But aircraft engineers carried out a different set of procedures due to confusion between Bond and Eurocopter staff during a phone call to the manufacturers.
It emerged after the tragedy that Eurocopter experts believed Bond engineers had discovered a problem with a different helicopter part.
A fatal accident inquiry into the men's deaths off the coast of Peterhead on April 1, 2009 is being held at the Town House in Aberdeen and is due to last six weeks.
Yesterday, lawyer Tom Marshall said the families of those who died wanted to know about the procedures in place which could have prevented the oil workers' deaths.
He said: "What precautions could have been taken to avoid the disaster, that's what the families want to know."
Former Bond maintenance manager John Crowther said engineers were being "very cautious" at the time of the crash because they were being scrutinised by air accident investigators. A Bond Super Puma had ditched near a BP oil platform in the North Sea in foggy conditions on February 18, 2009.
The 16 passengers and two crew had survived but at that time the cause of the incident was unknown. Air Accidents Investigation Branch staff were investigating Bond practices and procedures.
The inquiry heard that a similar problem with an epicyclic chip detector was uncovered on a Bond-operated helicopter in 2008.
Mr Crowther said he had not been aware of the problem with that aircraft in 2008 until after the tragedy the following year.