Autopilot fighting for control

If the autopilot is flying, use the autopilot console to fly
the airplane. Over-powering the autopilot is always BAD
technique. Many autopilots will disconnect if they sense a
problem which can include input on the control wheel.

Autopilots have a supplement in the POH, it should be read
and understood.



"Robert M. Gary" wrote in message
ups.com...
|
| Ron Natalie wrote:
| Robert M. Gary wrote:
| However, it is very easy to hand fly the plane while
the autopilot is
| on. The Cessna training instructors told us that they
routinely hand
| fly procedure holds on approach w/o changing the mode
on the autopilot,
| just over powering it.
|
| Ick. What's the point? Which mode where they in to
start with?
|
| The autopilot is in nav/approach mode. This is coupled
with a G1000 so
| it doesn't do holds on its own (its based on the 430
software, not the
| 480 software). So, rather than switch the autopilot into
heading mode,
| and then back into approach capture mode, they leave it in
approach
| mode. That way, as soon as you turn in bound you can just
let go and it
| flys the approach (KAP140 has pitch control and can fly a
GS). It just
| saves you from leaving nav mode and havnig to go back into
capture
| mode. I think part of their point is that it doesn't do
any harm to out
| mussle the autopilot.
|
| -Robert
|

Jim Macklin wrote:
If the autopilot is flying, use the autopilot console to fly
the airplane. Over-powering the autopilot is always BAD
technique. Many autopilots will disconnect if they sense a
problem which can include input on the control wheel.

I'm simply quoted chapter and verse what the Cessna factory instructors
are saying. If you have a disagreement with the technique you are free
to discuss it with them.

I will at the next pilot meeting that Cessna hosts in their
meeting room just south of the Wallace plant on K42. These
are regular CFI meetings jointly with the FAA and Cessna and
other groups.

BTW, the factory instructors can be wrong. Or the person
who reported to you could be wrong. Part of a good
autopilot checkout should include showing that the servos
are not so strong that a pilot can't maintain control. But
that is a demo, the correct procedure is the hand fly, with
or without the FD or use the A/P console to command the
airplane.

Of course if the object is to have a student get an airplane
with the trim 100% wrong...


--
James H. Macklin
ATP,CFI,A&P

"Robert M. Gary" wrote in message
ups.com...
|
| Jim Macklin wrote:
| If the autopilot is flying, use the autopilot console to
fly
| the airplane. Over-powering the autopilot is always BAD
| technique. Many autopilots will disconnect if they
sense a
| problem which can include input on the control wheel.
|
| I'm simply quoted chapter and verse what the Cessna
factory instructors
| are saying. If you have a disagreement with the technique
you are free
| to discuss it with them.
|

Jim Macklin wrote:
Of course if the object is to have a student get an airplane
with the trim 100% wrong...

How does hand flying a procedure turn effect the trim? I've not noticed
this myself. You think the role servos get confused and try to change
the pitch? I'm not following.
-Robert

Jim Macklin wrote:
If the autopilot is flying, use the autopilot console to fly
the airplane. Over-powering the autopilot is always BAD
technique. Many autopilots will disconnect if they sense a
problem which can include input on the control wheel.

Yep, caused an airliner to crash in Russia a few years back
(among other issues).

Ron Natalie wrote:
Jim Macklin wrote:
If the autopilot is flying, use the autopilot console to fly
the airplane. Over-powering the autopilot is always BAD
technique. Many autopilots will disconnect if they sense a
problem which can include input on the control wheel.

Yep, caused an airliner to crash in Russia a few years back
(among other issues).

Ok, if you're going to bring up an incident tell the entire story. The
captains 15 year old son was at the controls at the time.

-Robert

Robert M. Gary writes:

Ok, if you're going to bring up an incident tell the entire story. The
captains 15 year old son was at the controls at the time.

Michael Crichton's novel comes true! (Almost.)

--
Transpose mxsmanic and gmail to reach me by e-mail.

Mxsmanic wrote:
Robert M. Gary writes:

Ok, if you're going to bring up an incident tell the entire story. The
captains 15 year old son was at the controls at the time.

Michael Crichton's novel comes true! (Almost.)


Crichton's novel post dates (and was almost certainly influenced by)
the incident.

Robert M. Gary wrote:
Ron Natalie wrote:
Jim Macklin wrote:
If the autopilot is flying, use the autopilot console to fly
the airplane. Over-powering the autopilot is always BAD
technique. Many autopilots will disconnect if they sense a
problem which can include input on the control wheel.

Yep, caused an airliner to crash in Russia a few years back
(among other issues).

Ok, if you're going to bring up an incident tell the entire story. The
captains 15 year old son was at the controls at the time.

Yes, that was the cause of the AP disconnect. The 15 yo overpowered
the autopilot causing it to silently disconnect the aileron servos.
Neither the right seat pilot nor the captain standing behind noticed
this. When the airplane started roll subsequently they assumed they
had somehow commanded an autopilot-controlled hold entry. They
then allowed the bank to progress to 50 degrees.

This leads to an incipient problem you can have in a private aircraft
as well. Without sufficient power, the autopilot trying to maintain
altitude can drive the aircraft into a stall. It was finally at the
onset of the prestall buffeting that the copilot started to try to
recover, unfortunately while you can overpower an autopilot easily,
overpowering a 15yo holding the other yoke is not as easy.

Ron Natalie wrote:
Yes, that was the cause of the AP disconnect. The 15 yo overpowered
the autopilot causing it to silently disconnect the aileron servos.
Neither the right seat pilot nor the captain standing behind noticed
this. When the airplane started roll subsequently they assumed they
had somehow commanded an autopilot-controlled hold entry. They
then allowed the bank to progress to 50 degrees.

This leads to an incipient problem you can have in a private aircraft
as well. Without sufficient power, the autopilot trying to maintain
altitude can drive the aircraft into a stall. It was finally at the
onset of the prestall buffeting that the copilot started to try to
recover, unfortunately while you can overpower an autopilot easily,
overpowering a 15yo holding the other yoke is not as easy.

Its hard to compare an transport aircraft quality autopilot with an air
mixer. The specific problems brought up in the Russian accident were 1)
The pilots were never trained that overpowering the autopilot would
result in a *partial* disconnect. The roll disconnected but not the
pitch and 2) When such an event happens the autopilot disengage horn
does not sound. Clearly a misstep in design.

Now compare that to the Cessna. If you tell the Cessna to hold altitude
and pull power all the way back to idle it will get pretty slow, but it
will not stall, the nose will drop and the computer is smart enough to
give up altitude to prevent stall (I've done it). There is no partial
disconnect in the Cessna. The autopilot is either engaged or not. If
you press the red button the entire thing goes off line. In the above
accident a non-rated person was banking the aircraft in excess of 60
degrees of roll when the problem happened. If you use more than 60
degrees of roll in your procedure turn, you probably have bigger
problems in your Cessna than the autopilot.

-Robert