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REFLECTOR: Fuel system safety


The thoughtful responses to the query about fuel system safety are
appreciated.  I'll risk giving my summary, conclusions and philosophy; and
additional questions.

Obviously the best way to avoid a crash and burn is to not crash.  It is
expected that we will strive for a high level of flight worthiness; both for
ourselves and our machines.  We would do this even if there were no
flammable fuel onboard; there are plenty of other reasons.  Also, we know
that safety and reliability are related to simplicity; but the most simple
is not necessarily the safest and most reliable.  But we do know that
Velocity accidents happen; that an engine (related) in-flight fire has
happened, fuel leakage into the cabin has occurred as a result of an
accident, and a fatal accident has occurred in which the plane was destroyed
by fire.  These are very low probability events.  Sure we accept risks, but
the key is to know what they are and control them to whatever degree we
reasonably can.

There is no doubt that the "answers" to safety related aspects of the fuel
system in an accident are difficult or impossible.  In the cabin area I
think that the bottom line is that we rely on the considerable structural
strength of the spar, firewall, gear bulkhead and strake area to protect our
fuel system in the event of a mishap.  What's left is to look at the routing
and the materials of the fuel lines to minimize the likelihood of disruption
if things were to shift around a bit.  We should probably avoid having the
fuel lines going through any of the bulkhead structures; i.e., following the
standard design.  It may also be that using braided steel sheathed line with
threaded fittings, with some controlled slack in the line, provides the best
bet on things hanging together.

Question: Do we know the source of the fuel in the cabin in Hugh Hydes

Aft of the firewall things are different.  Protection of fuel lines from
heat (and fire) is standard operating procedure.  Here there are sources of
ignition for flammable vapors.  And here, in my opinion, there is also a
greater likelihood of a ruptured fuel line in the event of an accident.  If
one could keep ones head while about to do a forced landing, closing an
emergence shutoff valve before impact could reduce the chances of a
post-mishap fire.

Yes, installation of a valve introduces the tradeoff of the likelihood of
valve causing an accident by being inadvertently in the wrong position vs.
protecting from a fire.  I don't think that valves are so complex, or that
the installation can't be well enough thought out that the installation
doesn't win out.  Plus there is some added convenience and safety for filter
maintenance, etc.  Valves are simple and reliable, need to be periodically
inspected and can be replaced. And, absolutely, manual or electrical; either
installation needs careful consideration to be SURE that it cannot
inadvertently be in the wrong position.

Question:  Jim Agnew- what kind and where is your fuel shutoff switch?

Question:  Those using a manual valve with cable; what valve are you using?

In-flight engine fires?  If there is going to be one, it's going to be
fueled by an oil or fuel leak somewhere. And if it starts, any line that is
susceptible to fire damage is going to make the fire worse.  So fireproof
lines and a shutoff valve could reduce fire risk.

Question: Should we be using only solid steel lines aft of the firewall?  Or
is fire sheathed, stainless steel braid sheathed line just as good?

The addition of  fire detection would seem to make sense.  I'm not sure what
can be accomplished by looking in a rearview mirror AFTER your engine has
quit (why else would you look?) to see that you also have smoke and flames.
A little more timely warning may be helpful.

Question:  What are the reliable options for fire detection?

Last thoughts.  If we are going to call it a firewall, it should be
fireproof.  A nonflammable skin on the engine side (and a thin layer
fireproof insulation?) makes a lot of sense.  Perhaps the valve options are:
full simplicty; i.e.,  no valve - no fire detection; or, emergency shutoff
with fire detection.  Simplicity vs. knowledge and control.  I have no proof
of which is better.  You get to choose.

Further comments welcomed.

Al Gietzen