Rudder for final runway alignment (?)

Wade Hasbrouck writes:

Which misses the point of my statement... "What do you do if the autopilot
does not disengage or is 'jammed'?"

Which misses the point of my statement: With an autopilot, you have a
button that normally disengages it. And that normally works, even
when the rest of the autopilot fails. With fly-by-wire, you have
nothing; if the FBW system fails, you hit the side of a mountain, or
the ground. There is no button that disengages FBW. The first two
letters in FADEC stand for "full authority," meaning you can't
override it.

You need to be familiar with "What are
you going to do if it does not disengage or is 'jammed'?" I know there are
some procedures to follow for this situation, but not familiar with them as
the planes I fly do not have an autopilot.

FBW doesn't need any such procedures, since there is no way to
disengage FBW. If it fails, you're doomed ... simple.

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T o d d P a t t i s t writes:

Of course, you have
to believe the instruments as to where the horizon is for
these sensations to be reliable ...

If you have to believe the instruments in order to make the sensations
reliable, then the sensations are _not_ reliable--the instruments are.

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Mxsmanic schrieb:

Not really. It is certified to do the right thing. Name an accident
where an FBW system didn't.

Habsheim.
There's a reason why they call it the Scarebus.

Sigh. Yes, there is a reason. It's called ignorance.

Stefan

Stefan writes:

Sigh. Yes, there is a reason. It's called ignorance.

Not when flight recorders are spirited away for two weeks after an
accident.

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Dave,

He is in France. It's against the law.


See my comments in this thread (or another manic thread) about attempts
at humor by Americans about the French...

--
Thomas Borchert (EDDH)

T o d d P a t t i s t writes:

The direct sensation of acceleration is reliable, but like
the instruments has imperfect accuracy.

A sensation of acceleration alone is of limited utility. Unless you
can integrate the accelerations over time in a very accurate way, they
don't tell you much about where you are, or what attitude you are in.

The integrated
value of acceleration that you do in your head produces an
estimate of speed, and that value is less reliable. The
second integration that you do in your head is position, and
that value is even less reliable.

Yup.

I've been trying to give you the benefit of the doubt, but
you're not trying hard to understand this. Perhaps this
will make it clear - A full motion simulator can produce an
excellent simulation of many of the sensations we are
discussing. It's obvious that the full motion simulator
does not move thousands of feet the way that an airplane
does. How does it achieve excellent simulation without
moving out of the simulation box? It can do that because
humans are good at sensing accelerations, but not in
integrating them to get velocity or double integrating to
get position. The full motion sim matches the accelerations
pretty closely, but not so closely that it needs to really
leave the building that houses the sim.

The same thing happens in instrument flight and in VFR
flight - the pilot uses the sensed accelerations to fly, but
uses the horizon - either real or AI instrument simulated to
recalibrate his awareness of position and attitude. Without
the horizon, his beleif in position and attitude starts to
drift away from reality. He's excellent at detecting when
he starts to accelerate away from his current
position/attitude, but lousy at knowing what the current
position/attitude is.

So it would seem that the only utility of sensation is in assessing
extremely short-term movements of the aircraft. You may sense that
you've started to climb or descend, but you don't know how far, or how
fast. For movements and commands that take place over the scale of
seconds, that might be moderately useful, but beyond that it seems
that it's just good for feeling warm and fuzzy.

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T o d d P a t t i s t writes:

That's exactly the point. The sensations don't tell you
absolutes, they tell you when things are changing and how
quickly. Those are the sensations the skilled pilot uses to
know what the plane is about to do so he can react *before*
the aircraft significantly changes its position or attitude.

If he is able to instantly and correctly interpret the implications of
the acceleration he feels, which I would doubt it all but the most
ideal situations. I read constantly about how easy it is to be duped
by illusions in vision and sensation in aviation; there must be a
reason for all of these warnings. This newsgroup is the first time
I've seen anyone give sensations such priority. Every other source
warns about how misleading they can be.

Nope. When you are landing, you need to touch down in a
particular attitude. If you wait until the plane has
changed its attitude or position so much that it's visible
looking out the window, it may be too late in a critical
situation. You need to sense that it's starting to roll
left so you can correct it before it has changed.

Your artificial horizon should tell you immediately what attitude the
aircraft is in, if there's any doubt. And landing is a tightly
circumscribed environment compared to cruise flight.

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Mxsmanic,

Habsheim.

BS! Point me to where the FBW does something the pilot doesn't. In
Habsheim, the pilot did something the plane wasn't designed nor able to
do, namely extremely low flight in a wooded area. His last words were
probably along the lines of "Hey, watch this!". FBW had nothing to do
with it. The accident report reflects this.


There's a reason why they call it the Scarebus.


Yes. That reason is called "Boeing Marketing Department".

--
Thomas Borchert (EDDH)

T,

I've been trying to give you the benefit of the doubt, but
you're not trying hard to understand this.


Uhm, I don't think that's his intention.

--
Thomas Borchert (EDDH)

On Mon, 25 Sep 2006 23:23:16 +0200, Mxsmanic
wrote:

FBW doesn't need any such procedures, since there is no way to
disengage FBW. If it fails, you're doomed ... simple.

Don't underestimate the capabilities of a trained, experienced crew to
cope with equipment failure. Case in point, United flight 232 at Sioux
City, Iowa. Despite complete hydraulic loss and concomitant loss of
flight controls the crew was able to bring the aircraft to what turned
out to be a survivable crash for most of the occupants. Though the
outcome was not as favorable as we might have hoped, it was
considerably better than "doomed," and the flight crew can be fully
credited with that measure of success.

In-flight emergencies are like a box of chocolates, you never know
what you're gonna to get.

RK Henry