nuckolls.bob(at)aeroelect
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 Posted: Tue Jul 17, 2018 10:48 am Post subject: Failure Mode Effects Analysis |
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At 11:44 AM 7/17/2018, you wrote:
| Quote: | | Good point Joe, regarding future maintenance considerations. But that is not a safety issue. Bob said that the Bus Manager is poorly designed in that it appears to him that a proper FEMA analysis was not conducted. I'm not arguing the point, but I do think such a statement should be accompanied by the specifics that back up the opinion. (Much the same as if someone declared Bob's OV module is poorly designed without providing any specifics.) Incidentally, the "newfangled" OV module suffers a similar problem of very limited availability. |
Conducting an FEMA is a process of considering the
consequences of perhaps hundreds of simple failures
with respect to:
1. How are the ways that this particular component
can fail?
2. How would this particular failure manifest in
terms of system performance?
3. Does the failure elevate risk for a comfortable
termination of flight?
4. How would the pilot become aware of that failure?
5. Is the system fitted with a means by which that
failure can be mitigated?
6. Is the failure pre-flight detectable? If not,
should a means for pre-flight testing or in-flight
annunciation be incorporated?
Deducing the answer to these questions for EVERY
part of an airplane allows the competent and
experienced observer to write a report that speaks
to the rational for sprinkling holy-water on
the collection of parts that make up a component
of the overall system. FMEA can and should be
applied to every part of a system whether a nut
and screw or a transistor in the EFCI. To be
sure there are few really critical parts but unless
they are identified and accounted for, the system
is burdened with unnecessary and perhaps catastrophic
risk.
The goal is to achieve a high level of confidence
that the system is failure tolerant. This means
that probable failures are either (1) insignificant
with respect to comfortable termination of flight
or (2) have backup plans that makes the failure
insignificant.
This is the foundation for my assertions that
there should be no reason that OBAM aircraft
should not be fitted with out-of-reach fuse
panels. The ultimate salute to the FAA requirement
for carrying spares for all 'critical' fuses
is to eliminate all critical fuses.
Crew awareness of failures is an important
part of the analysis. I.e. no high risk
failure should be allowed to go
un-noticed . . . ideally, annunciated
in flight or identified during pre-flight.
Beyond the FMEA, there are cost of ownership
issues. Some of which are obvious based on
lessons learned; others that won't manifest
until the marketplace has a chance to conduct
the real-life studies.
My concerns for devices like EFII, EXP-Bus
extend beyond FMEA to also cover cost-of-
ownership and abandonment of legacy design
goals.
Bob . . .
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