Autopilot fighting for control

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.

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

Ron Natalie writes:

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.

The 15yo was trying to steer the aircraft the wrong way?

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

Mxsmanic wrote:
Ron Natalie writes:

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.

The 15yo was trying to steer the aircraft the wrong way?

The report I read theorized that the instructions that pilot
was shouting was interpretted as to hold the wheel in a neutral
position while the copilot was trying to roll the plane back level.

On Tue, 10 Oct 2006 21:35:47 -0500, "Jim Macklin"
wrote:

The Cessna instructors are probably showing that the servos
can be over-powered with pilot muscle, no reason to lose
control. But I'm sure they also teach the location of CWS,
the trim switch, the red disconnect button and the A/P CB
and avionics master.

There's no CWS on the KAP140 install in the NAV3 equipped Cessna line.
Probably on the Mustang when it comes out, but not the SEPs.

It's been a few years so things might be different now, but IIRC, the
class doesn't teach leaving things in NAV mode to fly procedure turns,
but teaches doing a partial-panel approach by selecting wing-level and
flying it that way. Personally with a working aircraft I always fly a
procedure turn w/ autopilot by changing it to HDG mode, flying the
procedure turn with the bug, and then re-arm APR on the inbound
intercept.

Peter Clark wrote:
..

There's no CWS on the KAP140 install in the NAV3 equipped Cessna line.
Probably on the Mustang when it comes out, but not the SEPs.

I've got CWS on my 55X. Frankly, I never use it.




Personally with a working aircraft I always fly a
procedure turn w/ autopilot by changing it to HDG mode, flying the
procedure turn with the bug, and then re-arm APR on the inbound
intercept.

That's what works for me. On the 55X, you can HDG+NAV+APR
at the same time and it holds the heading until the needle comes
alive (if you just NAV+APR, it may make a more agressive turn
towards the course).

On Thu, 12 Oct 2006 15:35:28 -0400, Ron Natalie
wrote:

That's what works for me. On the 55X, you can HDG+NAV+APR
at the same time and it holds the heading until the needle comes
alive (if you just NAV+APR, it may make a more agressive turn
towards the course).

Yea, same on the KAP140. I use HDG+APR and try for a 30-40deg
intercept angle. Seems to work.