yaw damper and auto throttle

[jethrocch 0]

I have been flying the PMDG 737 for a few months and I have 2 questions about the yaw damper and the auto throttle.  I would like to know what is the correct procedure.

 

1. Should I turn on the yaw damper at all times from engine start to parking?  The reason I ask this is that the aircraft seems to occillate (yaw) back and forth in flight even in light turbulence.  The acft can only remain smooth flight at perfectly smooth air.  Looking at the position of rudder, I am quite sure that this is due to the yaw damper action.  The rudder is moving left and right at nearly once per second.  When I switch off the yaw damper and center the rudder, everything stops and the acft flies smoothly.  What is the real world procedure here?

 

2. The FCOM seems to say that it is OK to leave the auto throttle on when manually flying the final approach.  When I push on the stick to steepen the descent, the throttle decreases automatically which is fine.  But when I flare at about 30 feet to slow a bit and reduce the descent rate, the auto throttle does not allow me to do so.  It keeps at the target speed and the throttle increases during flare.  I end up floating down the runway and have difficulty to land.  I have heard that the auto throttle would disengage automatically when touch down.  Should I disengage before flare?

 

Thanks a lot!

[Yosm 19]

Hello,

 

For the yaw damper i am not sure. Perhaps someone else can fill that one in. Did you try google?

 

For the Autothrottle. One should disengage prior to flare in order to get to idle trust when at approx. 10 ft.

Mostly flying the final approach manually is better for me. Makes me able to put her down better.

 

RGS,

 

Yori Smulders

[scandinavian13 5,192]

 

 

The reason I ask this is that the aircraft seems to occillate (yaw) back and forth in flight even in light turbulence.

 

The turbulence effect in FSX is implemented oddly, and will cause many high-end add-ons to have a little trouble.  The turbulence effect should be disabled in the FSX Settings.  It is normal to leave the yaw damper on.

 

 

 

2. The FCOM seems to say that it is OK to leave the auto throttle on when manually flying the final approach.  When I push on the stick to steepen the descent, the throttle decreases automatically which is fine.  But when I flare at about 30 feet to slow a bit and reduce the descent rate, the auto throttle does not allow me to do so.  It keeps at the target speed and the throttle increases during flare.  I end up floating down the runway and have difficulty to land.  I have heard that the auto throttle would disengage automatically when touch down.  Should I disengage before flare?

 

You're not using the autothrottle (AT) properly.  Your AT is trying to hold a certain speed.  Remember, this is a computer trying to help you do your job.  Granted, it'll autoland and do all of what you're asking, but it knows to do all of that because during an autoland, it is in full control.  When you're the one flying the plane, however, it cannot read your mind and will not assume it knows what you're doing.  Speed hold mode does only that - hold speed - regardless of your altitude or proximity to a runway.

 

Normally, the flare is meant to arrest your descent and bleed off speed.  That requires your speed to decrease, and you've told the AT to hold a speed.  That's its only job, and it'll do it until you tell it to stop.  Because of that, it adds thrust to maintain the speed you told it to if necessary.

 

Computers (the FMC) are not like people.  If I asked you to pick up the end of my couch so that I could vacuum under it, you'd pick up the end of the couch until you saw I'd moved on to other parts.  If I asked the same of a computer, it would hold it in that position until told otherwise.

 

Similarly, the AT is being told to hold a speed.  There is no button that says "hold the window speed until close to this runway, at this point, at this altitude AGL, and then reduce to idle."  The only time it puts that information together is when in APP mode, on autopilot, during a coupled landing (autoland).  Again, this is because it can predict its own actions.  You have to be the one to tell it to stop by turning off the AT.

 

When hand flying, it is Boeing's recommendation (with certain exceptions) that you also have the AT off.

[jethrocch 0]

Thanks.  I will not use the real world weather (update every 15 minutes) build-in feature anymore when flying this acft.  Once the acft stablize on glide slope, A/T off

The movement of rudder is quite large (half deflection frequently) when yaw damper is on.  I wonder whether this will exceed the structural limit of acft in high speed cruise flight.  All pessengers will sick and vomit in hours of oscillation.  Anyway, clear all weather from now on.

[scandinavian13 5,192]

Anyway, clear all weather from now on.

 

Just so you (and anyone who reads this later) know - that's not what I was saying.

 

I said check the "Disable turbulence and thermal effects on aircraft" box.  I would never tell someone to deprive themselves of realistic weather (unless I was trying to help them troubleshoot, and that would only be temporary).

 

[jethrocch 0]

Opps...... I did not check this box before.  This could be the major problem.  Thx

[scandinavian13 5,192]

Welcome.  That should fix the issue.

[justinpilotatc 5]

A good way to know if something needs to be on all the time is- if a master caution is triggered when its off then it should probably always be on unless an emergency checklist calls for it to be off.

[Fabo 213]

Regarding yaw damer - sometimes it is a bit slow to react when your computer is under a lot of load, which can happen often if your computer is a bit older, especially if the weather is bumpy.