I've cerified a few aeroplanes in the SEP class. If I may be forgiven the odd gross generalisation the job looks something like this...
- Preparing certification reports, 100+ hours
- Building an aeroplane, anywhere between 300-3000 hrs
- Flight testing, 1½-5 flying hrs for a simple series aeroplane, 25-50 hours for a new type or problem aeroplane, add in about 3 times that on top of the flying hours for preparation, planning, reporting, etc.
- Writing the Operating data, 10-40 hours with access to all the flight test reports.
So, the work of preparing a POH is fairly trivial in comparison to the rest of it. Given that in the UK at-least structural failure accidents are virtually unknown, whilst most accidents (including perhaps Pilotage's) are pilot-error related, a case could reasonably be made that the production (and use) of operating data should be done as rigorously as possible given that it's such a trivial part of the whole task.
As to liability, since there is already some agency (CAA/PFA) taking responsibility for approving the aircraft based upon Engineers' stuctural/certification reports, and finally approving the aircraft for Permit/CofA issue based upon the Test Pilots' reports, I'd have thought it perfectly reasonable for them then to approve a POH as-well.
G