Bad fuel gauges?

On Feb 24, 7:15*am, Bob Noel
wrote:
In article ,

wrote:
*A leak may be a very infrequent event, but
aviation safety is about being prepared for unlikely problems, rather
than unnecessarily relying on the gamble that it will never happen to
you.

But aviation safety is not about being prepared for every single problem
no matter how unlikely. *Aviation safety is about reducing the residual
risk to an acceptable level. *

Agreed. Or more precisely, it's about reducing the risk-to-cost ratio
to an acceptable level. Some particular small risk might be deemed
acceptable if it would cost $100,000 to avoid, but unacceptable if it
would cost $100 to avoid.

These levels are defined in AC 23.1309 and AC 25.1309.

The levels are implicitly defined throughout the FARs. For instance,
whenever some item of equipment is deemed necessary for airworthiness,
the FAA is thereby stipulating that the risk of not having that
equipment (in operable condition) is unacceptable, compared to the
cost of having and maintaining that equipment.

The Part 91 airworthiness regs (which pilots are required to know
before being allowed to solo) mandate a gauge that indicates the fuel
level in each tank. No specific accuracy is mandated, either in Part
91 or in the aircraft-certification regs in Part 23. So it becomes a
matter of common sense: a working fuel gauge has to be accurate enough
to serve its intended purpose, which (in familiar light GA planes
anyway) is to provide a rough cross-check of the consumption
calculations, to warn of a leak or other problem.

You've just added an "intended purpose" with the claim that the gauge
is there to warn of a leak, etc. *The reg states the intended purpose,
that is, to indicate the fuel level.

Indicating the fuel level is WHAT the gauge is required to do. We need
to consider WHY it's required to do that if we want to draw a common
sense conclusion about what kind of accuracy is required (since the
regs don't specify it quantitatively). If we can infer the gauge's
intended purpose, then common sense tells us the gauge is supposed to
be at least accurate enough to be usable for that purpose.

We all agree that fuel gauges are typically much less accurate than
flow calculations or flow measurements. Yet the FAA requires the
gauges, not just the calculations and flow measurements. And one
obvious reason is that the calculations and flow measurements don't
take into account the possibility of a leak. That's not a
controversial explanation, is it?