Good AI backup, wish me luck

In article ,
(Robert M. Gary) wrote:
I think you are missing something. If both AIs start showing different
results you will be suspecious and start asking questions. As I noted
a realistic AI failure situation can be very difficult to detect.

How is this fundamentally different than if one AI disagrees with the DG
and turn coordinator? I try not to stare at the AI the entire time, and
it seems that a scan would pick up a discrepency regardless of whether
it included a second AI. Now, flying the plane with a second AI may be
easier once the failed AI is identified, but I don't see how a second AI
would make identifying the failure any easier, because it would be a
required scan item just like the DG and turn and bank.


JKG

How is this fundamentally different than if one AI disagrees with the DG
and turn coordinator?


You don't know which to trust, and you are out of bullets. You have to figure
out which one is lying. Besides, you can bank while remaning straight, and
you can be level while turning.

With two AIs, you can go PP and use the TC and DG (and ball).

Jose

--
(for Email, make the obvious changes in my address)

In article ,
(Teacherjh) wrote:
You don't know which to trust, and you are out of bullets. You have to figure
out which one is lying. Besides, you can bank while remaning straight, and
you can be level while turning.

With two AIs, you can go PP and use the TC and DG (and ball).


If I have two AIs and they begin to disagree, what then? How do I
determine which one to believe?

If I incorporate the AI, DG, TC, wet compass, altimeter, and airspeed
into my scan and one instrument begins to disagree with the others, I
know almost instantly which instrument to disregard. Not sure how a
second AI helps substantially more with that, since it seems that I have
quite a few instruments to reference without the second AI. The second
AI would probably help me fly the airplane after I identified a faulty
AI, but wouldn't contribute substantially more to recognition because
I'd still have to use the other instruments in the panel to identify
which of the two AIs is accurate.

And, I flew partial panel in actual IMC just fine with *NO* AI many
times during my instrument training. The AI was covered and I knew that
I "lost" it, but I certainly didn't need a second AI to fly partial
panel, even on approaches.

I don't mean to make things sound trivial, because they're not.
Recognition and recovery is definitely not trivial for something like an
AI (I've had an AI die on me). However, thinking that a second AI is
going to bail your butt out of the recognition game is dangerous, IMO.
It all comes down to practice and practice often, which I suspect that
many of us (myself included) don't do enough of.



JKG

Jonathan Goodish wrote in message ...
In article ,
(Robert M. Gary) wrote:
I think you are missing something. If both AIs start showing different
results you will be suspecious and start asking questions. As I noted
a realistic AI failure situation can be very difficult to detect.

How is this fundamentally different than if one AI disagrees with the DG
and turn coordinator?

Because, a real world situation is that the AI dies very, very slowly.
There isn't that immediate "hmm, somethings wrong" like with a dead
vac (alarms going off etc). The TC has enough bounce in it that there
is really no way to detect small differences like 5 degrees when you
are in real IMC. Once you start bouncing around in the clouds the TC
starts bouncing back and forth. It will keep you upright but is far
from close enough to determine 5 or perhaps even 10 degrees off. The
DG you may or may not notice. In anycase two AIs being off is a pretty
quick and certain thing to notice.

Couple that with the fact that you have to decide which is right, the
TC or the AI. If you have 3 its easier to pick on that might be bad.

In article ,
(Robert M. Gary) wrote:
Because, a real world situation is that the AI dies very, very slowly.
There isn't that immediate "hmm, somethings wrong" like with a dead
vac (alarms going off etc). The TC has enough bounce in it that there
is really no way to detect small differences like 5 degrees when you
are in real IMC. Once you start bouncing around in the clouds the TC
starts bouncing back and forth. It will keep you upright but is far
from close enough to determine 5 or perhaps even 10 degrees off. The
DG you may or may not notice. In anycase two AIs being off is a pretty
quick and certain thing to notice.

Couple that with the fact that you have to decide which is right, the
TC or the AI. If you have 3 its easier to pick on that might be bad.


Let's see, I have 4 instruments in a basic IFR panel that can indicate
the position of the wings. AI, DG, TC, and wet compass. If my AI
starts to roll over 5 or 10 degrees and I level it, that's not going to
put me in a death spiral, but I should notice heading changes regardless
of what the TC is doing. If the ride is so rough that you can't obtain
meaningful data from any of the other instruments, then you're not the
guy I'd send to buy my lottery ticket.

Bottom line is that a scan should include all instruments. The more
data you incorporate into your scan, the more data you'll have to work
with if something looks amiss. The TC isn't the only practical backup
for the AI and, in fact, provides no pitch information anyway; for that,
you'll have to include airspeed and altimeter.

If I had to pick between having the TC, DG, altimeter, and airspeed as
my AI backup, or picking a second AI, I'd take the data from 4
instruments rather than one.

Maybe it's just me. Wouldn't be the first time.



JKG

Jonathan Goodish wrote in message ...
In article ,
(Robert M. Gary) wrote:

Let's see, I have 4 instruments in a basic IFR panel that can indicate
the position of the wings. AI, DG, TC, and wet compass. If my AI
starts to roll over 5 or 10 degrees and I level it, that's not going to
put me in a death spiral, but I should notice heading changes regardless
of what the TC is doing. If the ride is so rough that you can't obtain
meaningful data from any of the other instruments, then you're not the
guy I'd send to buy my lottery ticket.

Its very common for me to be in actual conditions that are bouncy
enough that the TC isn't going to do anything other than keep me
upright. I'd be banking back and forth like a mad man as it flopped
around. The compass is pretty useless, it just spins back and forth.
That's the problem with most IFR, its usually very, very bouncy.

If I had to pick between having the TC, DG, altimeter, and airspeed as
my AI backup, or picking a second AI, I'd take the data from 4
instruments rather than one.

But its not one, its two. If you look at the two AIs and they disagree
you will say to yourself "Hmmm, something is wrong". The ability to
say that is HUGE. A real AI failure is so mild that you probably would
never notice. If just using the TC, DG and compass worked, you
wouldn't hear about people dieing after partial panel situations. You
wouldn't see big warnings on vac pumps. The airlines decided to get
extra AIs and dump the TC a while ago.