It may be very difficult to form a meaningful assessment of the safety impact of FBW.
First, very few successes are reported; the industry loves to focus on failure.
Second, any differences in the mechanism of control should not directly affect the pilot’s ability to fly (operate) the aircraft. Only envelope protection might stand out as a difference, but even non FBW have some protection – stick force, audio/visual warnings, and the scenarios are rare.
Beyond controls, the safety technologies apply to both types with/without FBW (EGPWS, TCAS, etc), and any detrimental aspects are predominately related to human behavior; particular situation assessment.
EFIS displays etc, might show some benefit with increased information, but see (1). The display of terrain and pop-up alerts for EGPWS might accentuate the warning, and thus contribute to the success of EGPWS.
EICAS displays may aid better fault finding, but there may be fewer faults to find.
Overall this is the area of maximum safety benefit.
I would play-down any automation / skills controversy as each type has the capability for automation/enhanced technology, where any differences are in the level of automation and possibly manufacturer dependent, but none reliant on FBW.
Perhaps the major difference is in training; the extent appears to have reduced, but arguably with more complex systems and greater capability, systems training should have increased. As a result crews are expected the ‘trust’ automation based on minimum knowledge and depend on ‘procedural’ guidance.
As a result, in many instances crews may choose to rely more on technology, attempt to follow SOPs when they might not apply, and seek ‘legal’ cover vice airmanship (understanding of the operational scenario).
However, don’t tie these in with FBW, they result from deliberate human-choice driven by economics. Thus a suitable measure might be of continued success of the industry vs the safety record – at what cost. Most indicators would show a positive swing of the pendulum, yet many forums/posts suggest otherwise. On one hand that’s good (never forget to be afraid), on the other it’s human fickleness. Perhaps we should ask what has the human has contributed to the swing; plus, minus, or interestingly frustrating.