EASA/FAA STCs
IO-540. I specifically mentioned 'significantly better certification data' as opposed directly to imnproved safety, but the two are directly related. Here is a recent example (which we have made subject to a formal investigation so I'll keep details a bit vague):
Aircraft (no, not the KingAir you mentioned in another post!) had dual GNS units installed to FAA AML data with interface to a dual EFIS display. The installer did not create/provide any wiring diagrams of what they'd done. On test as part of import, it was found that each EHSI would annunciate 'LOC' when the associated GNS was tuned to ILS - so far so good, but L-R deviation was actually being driven by GPS XTK deviation. Potentially lethal as Nav flag was clearing from ILS but wrong deviation source, so pilot could consider himself on centreline whilst possibly flying into a mountain! There were other related problems in cross-side switching, autopilot coupling and RMI pointer operation. I've no idea of how the installer could have certified the completed installation as functionally correct.
A European STC requires specific design data including wiring diagrams for the particular airframe and avionic interface. If this had been done, the designer should have been able to work out that the generic AML drawings were seriously wrong! We suspect other similar installations based on this data are out there and have already identified at least one more aircraft with similar issues.
This is probably the extreme end of what I find wrong with FAA AMLs, and I agree that EASA may well go over the top with some of it's requirements. This incident shows that relying on generic installation data as contained in most AMLs leaves potentially dangerous situations open which may never be reviewed by another design/certification engineer. At least in forcing the applicant to produce a full design package, EASA provide an additional layer of checking manufacturer-produced installation data as well as producing specific test schedules hich should identify post-installation issues.