Routine inspections, known as G-CHECKS, were required to be carried out on all aircraft when they had logged 7,500 flying hours.
Several new helicopters had been ordered by Bond to ferry oil workers offshore as part of a BP contract in 2004.
Yesterday Bond maintenance manager John Crowther, told the fatal accident inquiry in Aberdeen that the firm had to vary aircraft flying hours so they would not all be due inspections at the same time.
He said it would seriously affect company operations if all the aircraft reached their 7,500 flying hour limits because maintenance work could take up to eight weeks to complete.
Log book records for the AS332-L2 shown to the inquiry yesterday revealed that most gearbox components had been replaced on the AS332-L2 aircraft in April 2008.
Mr Crowther told the inquiry that it was a Civil Aviation Authority requirement at the time for log books to document major works on individual aircraft.
He said: “Every 3,000 (flying) hours the gearbox had to go back to Eurocopter and be completely stripped and be overhauled.
“Roughly every two years it would go back for an overhaul at Eurocopter.
“The only time we would ever see inside a gearbox would be if we were changing a module.”
He told the inquiry that the record showed that the main gearbox had been replaced along with the right hand module and the epicyclic component.
Mr Crowther said: “It looks like the left hand module was replaced later because it still had life in it.”
The inquiry continues.