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Changing direction at cruise 737-800


Theo Van De Griendt
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When ever I am flying a route in my zibo 738 on x-plane 11, I always wonder how they turn the plane from one airway to another without me noticing. I do not really understand how they do this because when I approach the next airway my autopilot decides to turn at a bank angle of 20 degrees which would not be very comfortable irl. Do pilots in real life just turn the plane really slowly?

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Most autopilots will typically bank anywhere between 25-30 degrees below FL250 and around 12-15 degrees above FL250. This is due to the loss of lift experienced while turning at higher altitudes.

However, I really don't think this is what you are experiencing. First of all, it generally is hard to feel/visualize the control movements as a passenger. A good example of this is while the airplane is in a cloud... 9 times out of 10 you probably wouldn't know if the aircraft was turning left or right as a passenger. Pilots have a better grasp of what is going on because they are looking at the instruments.

But I think the biggest factor is that most routes are generally straight and attempt to follow a great circle routing. This means that there are very few "bends" in the route where a large change in direction is required. Also, in the real world, ATC are constantly giving shortcuts to aircraft which tends to "straighten" the route significantly.

Hope this helps.

 

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There is a very good youtube channel (fd2sim), presented by a real 738 pilot, and he says that at his company they will set the turn rate knob to 10 above FL300.

Zibo has already adopted that same procedure, so if you are flying Zibo above FL300, even the AP will turn at 10 degrees maximum. That was implemented recently, I believe.

Cheers

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On 4/7/2019 at 4:31 AM, Mytho Leal said:

There is a very good youtube channel (fd2sim), presented by a real 738 pilot, and he says that at his company they will set the turn rate knob to 10 above FL300.

Zibo has already adopted that same procedure, so if you are flying Zibo above FL300, even the AP will turn at 10 degrees maximum. That was implemented recently, I believe.

Cheers

Wouldn't LNAV override the turn rate knob in all phases of flight? My understanding is that in heading mode you can control bank by setting the knob, but when LNAV is engaged, autopilot will adjust bank up to 30 deg to stay on track. I am sure lift factor is built into the bank calculation at high altitudes. 

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Hello,

 

This is a old post but as I am new around here I like to take a look into whats going on around.

I would just like to add a comment which is a key element for this topic. Most of the turns are coordinated turns, meaning that for a certain bank/aileron deflection, there will be a corresponding rudder movement too, in order to keep the turn a coordinated one (ball and stick also applies for heavy metal). Without the rudder in the equation, all turns would be felt by the passangers, especially the ones at the rear end.

 

If you look into vertigo awareness and upset recovery training, one of the technices used is manipulation of flight controls to give a sense of turn when at times you not turning, or vice-versa, you dont feel any turn and you are in a turn.

 

So, not all the movement done by the aircraft is felt by the passagers or even the crew (just ask cabin crew if they feel a turn or not, you'll be surprised). Thats why monitoring instruments is so, so important.

 

Happy flying all

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On 6/8/2019 at 12:22 AM, Ian v. said:

LNAV will determine the right bank angle automatically. Setting the bank angle knob to 10 degrees above FL300 is a precaution in case LNAV disengages during cruise and HDG select has to be used.

Indeed LNAV determines the bankangle required according to the difference in track required between the 2 airways. In the airline I fly for we dont set any bank limit during cruise or any face of flight. The auto setting works just perfect . Btw im talking B777, dont know anything about an Airbus . 

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