Hi Luciano,
Basically, each company has an internal audit plan (usually the annual one). Few companies use exactly the same program for many years (like auditing one element once a year), while the standard requires to adjust the frequency of processes audited according to the nature of non-conformances or customer complaints. So if the company gets a major NC for specific process, this process should be audited more frequently, so if it was once a year, now the internal audit plan should be updated to include audit of this element two - three times a year till the company gets better control over the process.
This is often where most companies go off the rails, straight away. Although John Broomfield suggests that audits are planned (already) based on status and importance, I've yet to find anyone who can give a good account of what that means. The default always seems to be based on the standard or something equally banal.
The fact is, taking a once a year audit and doing it twice or three times is not putting any thought behind the scheduling! Although the frequency should increase, it's true, in reality, changing the frequency (alone) isn't sufficient and the 'status' of the process has to be considered again and again.
If you consider the various stages that a complaint goes through, to resolution, might actually be the driver for auditing, wouldn't it be deemed serious enough that a small, focused audit would be done as each step of the
8D - for example - is implemented? We know, too many times there's little to no validation that the planned actions are actually taken, so the audit should give that 'independent' view of what's going on.
Taking an arbitrary approach to auditing from yearly to semi-annually or quarterly without any other considerations is missing the pont, IMHO...