Pireps
Ian,
Whenever a defect or comment is written into the Tech Log it is transfered, along with the rectification action taken, into the airline's maintenance organistion computer system. Each defect is given a specific ATA code, for example Air Conditioning defects are chaper 21, hydraulic are chapter 29. The codes are further broken down to indicate a more specfic area of the system.
This information (PIREPS - Pilot Reports) is used by maintenance organisations to monitor aircraft reliability, recurring/repetative defects, rogue components etc.
However, I suspect that if you ran a PIREP report against home reported 'defects' compared to defects raised at outstations, you may well see an 80/20 split. However you need to be very carefull the way you interpret this - it does not mean that pilots are carrying derects to home base. Many 'defects' are observations to give engineers a heads-up of a developing problem e.g. "no1 pneumatic pressure is reading 50 psi lower than no.2". Not in itself a defect - the pressures may be in limits - but a possible indicatiion of a Pressure Reducing Valve about to give trouble.
You know what they say about statistics!
Hope this helps
Bizdev