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Dave writes:
<< Ok, now I'm scared.>>
Join the club. I am not going to name names as I don't want to get into a
fire fight BUT you are free to ask the manufacturers what kinds of testing
they do to qualify their hardware. Ask to see the test results. If you get
some BS like "We plan to do the testing" or "Testing is too expensive" or
"The testing was done under contract and we are not at liberty to share the
results" or "We don't need to test as we haven't had any complaints" or "our
engineers are sure it would pass if we tested it" you will have your answer.
Dynon is a company with the RIGHT attitude (NPI). At last year's OSH (02)
they introduced their product saying "It's not for sale UNTIL we are sure
it is a solid product". It took them another year to get it right. http://www.dynondevelopment.com
Brian writes:
<<Why do
you suggest that having an EFIS display (or two on separate busses) and
a backup electrical gyro or T&B is any more unsafe than the traditional
setup of a vacuum gyro and an electric T&B?>>
I didn't. You inferred incorrectly. IMHO an electric gyro on a redundant
bus is more reliable than a pneumatic gyro with a pump.
It is legally OK to fly IMC behind an experimental EFIS as long as you have
a mechanical TSO'ed "primary" gyro, and all the other required TSO'ed equipment.
Fine. What I wanted to emphasize is that when the EFIS goes TU it may present
a compelling picture that you WANT to follow even though you know it is wrong.
Your brain wants to lock on to the big color image and it is surprisingly
difficult to ignore it and the best thing to to is to cover or turn off the
display. When I experienced it I found it extremely disorienting, to a level
I had not felt since my early IFR training days in actual IMC. Throw another
problem on top of that and you are in for Mr. Toad's Wild Ride.
Some EFIS systems (including some that are certified) use airdata to stabilize
the AHRS. Forget to turn on pitot heat (I'll bet you have never done that
;-) ) and you will lose
Airspeed, Altitude, VSI AND EFIS Attitude. You ready for that??
Some EFIS systems are sensitive to low voltage. This is true for systems
that "can't be on during cranking". So now you are night IMC on approach
with all the lights on. You put down the gear and the hydraulic pump cycles,
pulling the buss voltage down to 7 volts. The AHRS' microprocessor scrambles
and there is no watchdog to detect and reset the problem. You are really
fighting the localizer / glideslope and are fixating on the needles. You
are 4 dots left and 3 dots low when you finally cross check your mechanical
gyro. It shows a 45 degree bank and the GPS has you 30 degrees off course.
The briefer told you about the construction crane but that information can't
be processed over the other, more pressing matters. You ready for that??
Risk and risk management is a big part of flying. Knowing the risks, training
for them and accepting them is what every pilot does. It is not a good idea
to be ignorant of the risks. What you don't know can kill you. Some EFIS
systems are fragile compared to others. Robustness costs money. How much
is your life worth?
Do the research and know the risks before accepting them. Never trust what
someone tells you if they are trying to sell you something. Make them prove
it. Talk to other customers. Talk to installers. Take a demo flight where
YOU call the shots, not just a canned demo. Read the manual (there better
be a manual) that would come with the system.
Remember all that partial panel work you practiced and all those tips your
flight instructor gave you about detecting and acting on a failed instrument?
Well, EFIS systems are developing faster than that the training to support
them. Some of your training induced self confidence may be misplaced or unjustified
if you apply it to EFIS. You may want to keep that in mind.
Remember the first rule of Naval Aviation "Everyone is trying to kill you".
It is your life. Work to preserve it.
Regards
Brent Regan
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