kmanning

Auto-Pilot is NOT Engaging

Recommended Posts

Posted (edited)

I've been very angry about this but the auto-pilot has not been engaging when I press it. It has done this on the 747 version 3 for the P3D and the 737NGX. Last night, I was flying the 737NGX and after departing Charlotte International at about 2 to 3 thousand feet, I pressed the auto-pilot button and it will not engage. What's the damned problem? I was not able to engage it until after reaching 37,000 feet, and after about 5 to 10 minutes, it finally engaged. It has engaged in the past and I'm using the same technique as I've always have. Yes, I've set the trim control, but the FS2Crew always comes behind me and resets it, but as far as know, it still should work. It is NOT doing what it's supposed to do.

Ken.

Edited by kmanning

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

51 minutes ago, kmanning said:

It is NOT doing what it's supposed to do.

It actually probably is. The real autopilot will actually disengage if you keep pressure on the controls. Sounds like you have a hardware trim axis that is not being set to zero before you're engaging the AP.

It's usually a good practice to consider yourself as a cause before pointing the finger elsewhere, honestly. It's not a fun exercise to engage in, but to err is human, and more often than not, it's not the plane causing the issue.

  • Like 5

Share this post


Link to post
Share on other sites
Posted (edited)
1 hour ago, scandinavian13 said:

It actually probably is. The real autopilot will actually disengage if you keep pressure on the controls. Sounds like you have a hardware trim axis that is not being set to zero before you're engaging the AP.

It's usually a good practice to consider yourself as a cause before pointing the finger elsewhere, honestly. It's not a fun exercise to engage in, but to err is human, and more often than not, it's not the plane causing the issue.

I did not say it was the airplane that was causing the issue, and NO it's definitely no me for I'm using the correct technique. You've also have missed the point. I already know that the real aircraft auto-pilot will disengage if you put pressure on the control wheel, but that is not what's occurring, although it has done this with the 747. It WILL NOT engage when I press the auto-pilot. I've also mentioned that I set the trim control prior to leaving the gate, and I've always done this, as well as in the 747. When I'm in the climb, I'm following the flight director bars, as I'm supposed to, and it's right on the money when I engage the auto-pilot. So, there is NO reason for it to not engage, unless something is wrong with my controller. I've calibrated and I don't see any problem with it. So, what else is there? The technique I've used is by the manual, so it's not human error in this case. You say it sound like the trim axis is not being set to zero, and that's what it sounds like to me, But as I said, I set the trim to the correct position prior to leaving the gate. How do I check to make sure the trim is set to zero as you say? The FMC gives a trim setting of around 5.5 to 6.0. Is there something that I might have ticked in the FMC menu options settings that could cause it? The only thing I can think of is my controller.

Let me mention this because this could play a part. I have the Microsoft Sidewinder Force Feedback 2. Will disconnecting the force feedback cable cause this problem? I disconnected it because I don't like the return to center force that occurs in P3D. If I use FSX, I don't have this return to center force but when I fly using the P3D, the joystick has the return to center force, which is not realistic in the real aircraft, not in a real Cessna nor the real 737.

Ken. 

 

Edited by kmanning

Share this post


Link to post
Share on other sites
1 hour ago, kmanning said:

How do I check to make sure the trim is set to zero as you say?

You have to check your hardware assignments in the sim to be sure the sim hasn't assigned an axis to a trim axis.

When you're trying to engage the AP, you need to have the plane trimmed to the point where you can let go of the yoke and it will continue in the same direction without you stepping in to correct it. No nose drop, no climb, no turns - in trim.

Alternatively (and less realistically), you can disable "realistic AP engagement," and set "ignore hardware when AP is on" in the PMDG SETUP > menu of the CDU.

Share this post


Link to post
Share on other sites

Check to be sure that you have enough "null zone" on your yoke.  It there isn't, it will disengage the AP.

Also be sure before you take off that you select (arm) a lateral control on the MCP.  Either LNAV or HDG.  If you don't the AP will go to CWS (control wheel steering).

Also check in the FMC PMDG Options to be sure that you don't have an autopilot option set that would make it harder to engage.  I like "Realistic Autopilot" buy you might want to try to turn that off and see if it helps.

Share this post


Link to post
Share on other sites

Ken,

There are thousands upon thousands of good folks hanging around here who can help you with any problem you might ever conceivably have.

Simming is a hobby.  Emotion should never play a role in it. 

If you are having trouble getting something to operate- simply swing through here and say:  "I'm having trouble with ________"

You will get a ton of help.

 

  • Like 4

Share this post


Link to post
Share on other sites
Posted (edited)
16 hours ago, scandinavian13 said:

You have to check your hardware assignments in the sim to be sure the sim hasn't assigned an axis to a trim axis.

Hi Kyle,

As far as I know, I don't think another assignment is using the axis for the trim. The only one I've made changes to are the ones assigned by the FS2Crew for the PMDG 737NGX. I'm using the C and F keys.

Quote

When you're trying to engage the AP, you need to have the plane trimmed to the point where you can let go of the yoke and it will continue in the same direction without you stepping in to correct it. No nose drop, no climb, no turns - in trim.

Let me be sure I understand your answer because it doesn't quite makes sense to me. When you said "No Climb." did you mean no pitching of the nose, because when the airplane is taking off, it's in the climb. I don't press the auto-pilot button until I've achieved a constant pitch, following the flight director bar, and when it's fixed, I then press the button. I agree with you that I would have to have the plane trimmed to where it maintains the same direction it's going. But when I set the trim prior to leaving the gate that's given by the FMC, is that exactly what I'm doing, setting the trim for this take-off pitch? And when the flight director bar is fixed, its it not trimmed to the point where the auto-pilot should engage when I press it?

 

Quote

Alternatively (and less realistically), you can disable "realistic AP engagement," and set "ignore hardware when AP is on" in the PMDG SETUP > menu of the CDU.

I think I would rather use the more realistic setting. I'm begging to think that the problem is in my controller.

Ken.

Edited by kmanning

Share this post


Link to post
Share on other sites
16 hours ago, signmanbob said:

Also be sure before you take off that you select (arm) a lateral control on the MCP.  Either LNAV or HDG.  If you don't the AP will go to CWS (control wheel steering).

I've never had it to go to CWS. It would just never engage when I press the auto-pilot button. But I do need to check the null zones to be sure they're not tight. They should be fine because I've never moved them, and should be set at their default.

 

16 hours ago, signmanbob said:

Also check in the FMC PMDG Options to be sure that you don't have an autopilot option set that would make it harder to engage.  I like "Realistic Autopilot" buy you might want to try to turn that off and see if it helps.

I prefer the realistic.

 

Ken.

Share this post


Link to post
Share on other sites
Posted (edited)
42 minutes ago, kmanning said:

But when I set the trim prior to leaving the gate that's given by the FMC, is that exactly what I'm doing, setting the trim for this take-off pitch? And when the flight director bar is fixed, its it not trimmed to the point where the auto-pilot should engage when I press it?

No, you need to use trim after takeoff so the aircraft climbs at the same pitch that the flight director indicates without any input from you. You should be able to take your hands off the controls and have no pitch change. At that point the AP should engage without issues.

Edited by BrianW

Share this post


Link to post
Share on other sites

Ken,

The correct phrase here is that the airplane should be "in trim."  What we mean when we say this, is that you can take your hands off the controls and the airplane won't show a strong tendency to change pitch or roll from where you have it currently.

Obviously, if you are climbing, it will eventually lose a bit of airspeed and the pitch will naturally lower- but what we are talking about is that being "in trim" means the airplane is naturally going where you have it pointed currently- you do not have to hold control pressure to keep it on the desired pitch/roll.

Does that help?

 

  • Like 1

Share this post


Link to post
Share on other sites
6 hours ago, kmanning said:

But when I set the trim prior to leaving the gate that's given by the FMC, is that exactly what I'm doing, setting the trim for this take-off pitch? And when the flight director bar is fixed, its it not trimmed to the point where the auto-pilot should engage when I press it?

I think there's something you're getting confused here. Setting your trim for take-off is exactly that, setting it JUST for take-off. Once you're airborne, you need to set your trim accordingly, and for that, you don't even bother looking at the trim indicator anymore. At that point, you just go based off of feel. Once the plane is maintaining the desired pitch without you having to maintain directional control (in other words, the plane will fly at the pitch you want even with your hands off the controls), you're in trim.

  • Like 1

Share this post


Link to post
Share on other sites
1 hour ago, Captain Kevin said:

At that point, you just go based off of feel. Once the plane is maintaining the desired pitch without you having to maintain directional control (in other words, the plane will fly at the pitch you want even with your hands off the controls), you're in trim.

Hi Kevin,

I see where you're coming from. Since you say that I would go by the feel of pressure of my joystick, I would trim it so that it will be in trim when the joystick is in it's center position. But my joystick is not set for return to center position. In other words, there is no pressure. It moves smoothly as in the real aircraft when you move the yoke.

Ken.

Share this post


Link to post
Share on other sites
4 minutes ago, kmanning said:

I see where you're coming from. Since you say that I would go by the feel of pressure of my joystick, I would trim it so that it will be in trim when the joystick is in it's center position. But my joystick is not set for return to center position. In other words, there is no pressure. It moves smoothly as in the real aircraft when you move the yoke.

No, that's not quite what I meant. Basically, if you're still having to move your stick just to maintain the pitch that you're trying to maintain, you're not in trim. If the plane's flying the desired pitch even with your hands off the controls, then you're in trim. The main point being that after take-off, you can ignore the trim indicator. The trim you set for take-off is just for take-off. After take-off, you trim the aircraft as necessary.

Share this post


Link to post
Share on other sites
Posted (edited)

Ken,

the Boeing yoke has a center position. It‘s returning there when the elevator tab returns to its center position. Trimming an airliner isn‘t made by trim tabs on the elevator but by moving the whole stabilizer. Think of the stabilizer as a wing that is mounted vice versa. It holds the tail down so the nose doesn‘t drop. Moving the elevator now changes the profile of the „wing“, like flaps. So all you do for takeoff is setting an angle of attack of the stabilizer that neutralizes the weight of the nose at Vr. And that’s what you do in flight too when you trim the airplane. 

In case of your sudden autopilot issue... have you tried using the default panelstate? 

Edited by Ephedrin
Some wrong words

Share this post


Link to post
Share on other sites
2 hours ago, rsrandazzo said:

Ken,

The correct phrase here is that the airplane should be "in trim."  What we mean when we say this, is that you can take your hands off the controls and the airplane won't show a strong tendency to change pitch or roll from where you have it currently.

Yes, that's basically what it does when I have the flight director bar and airspeed on cue, that is V2 + 20.

2 hours ago, rsrandazzo said:

Obviously, if you are climbing, it will eventually lose a bit of airspeed and the pitch will naturally lower

It doesn't lose airspeed. It will maintain V2 + 20 as long as I follow the flight director bar commands. This is usually when I engage the auto-pilot.

2 hours ago, rsrandazzo said:

 but what we are talking about is that being "in trim" means the airplane is naturally going where you have it pointed currently- you do not have to hold control pressure to keep it on the desired pitch/roll.

Does that help?

Yes, I understand. But what I'm confused about now is that I'm being told that I need to trim the aircraft after take-off, and I've never had to do that in the past. I've always just pull back on the yoke at Vr, pitch the airplane to about 15 degrees and follow the flight director commands to maintain a climb of V2 + 20. Then I was able to engage the auto-pilot. I went back and reviewed all of the manuals for this phase of flight, including the tutorials, and none of them mentions anything about trimming the aircraft during this phase of the flight. It just mentions the procedures I've just mentioned above. I've always assumed that the trim control automatically adjusts to different phases of flight, and that's the noise that one hears in the cockpit. The yoke has an electric trim control but it was my understanding that the FCTM discourage pilots from using them, and recommend that pilots use the yoke during this phase of flight.

Ken.

 

Share this post


Link to post
Share on other sites

Trimming doesn‘t need tonbe mentioned in a manual, it‘s basic part of initial flight training, long before an airliner‘s FCOM comes into account. 

And no, pilots definitely are not discouraged to trim. They are only done so to use the trim instead of pulling/pushing the yoke to move the nose up or down. Basically the trim is used to neutralize the forces that have to be applied. Holding back a yoke of a 737 or 744 is exhausting. There are really heavy forces on your muscles if you have to do that over a longer period. 

And in manual flight no boeing will move the stab trim itself. That‘s not an airbus. You don‘t command the airplane, you fly it. Different philosophy.

as you say you could engange the AP like this in the past I could imagine that the „easy“ engagement was activated accidentally.

Share this post


Link to post
Share on other sites
1 hour ago, Captain Kevin said:

if you're still having to move your stick just to maintain the pitch that you're trying to maintain, you're not in trim.

Hi Kevin,

No, I'm not having to move my joystick just to maintain the pitch. The only time I'm moving the stick is when I rotate to raise the nose up and then pitch the airplane so that it follow the flight director commands. Once I have achieved that, it stays there for the most part. In other words, I'm not having to move the joystick back and forth just to maintain a certain pitch.

 

1 hour ago, Captain Kevin said:

If the plane's flying the desired pitch even with your hands off the controls, then you're in trim.

That's basically what the airplane is doing.

Ken.

Share this post


Link to post
Share on other sites
7 hours ago, kmanning said:

Hi Kevin,

No, I'm not having to move my joystick just to maintain the pitch. The only time I'm moving the stick is when I rotate to raise the nose up and then pitch the airplane so that it follow the flight director commands. Once I have achieved that, it stays there for the most part. In other words, I'm not having to move the joystick back and forth just to maintain a certain pitch.

 

That's basically what the airplane is doing.

Ken.

I’m not clear as to whether your joystick has a centering spring to return the stick to a neutral position when you let go of it. Most do, but if yours does not, that is probably part of the problem, as it makes it difficult to “feel”when the aircraft is out of trim.

If the joystick pitch axis is accurate, it would probably be quite easy to match (and hold) the flight director command bars in the initial climb. But if the horizontal stab is out of trim, you would be commanding up elevator deflection to hold your desired pitch, and that is what the autopilot does not “like”. What the autopilot wants to “see” is the elevators at neutral before it will connect. The only way to have the elevators at neutral in a climb is to have the proper amount of nose up stabilizer trim.

The FMS-derived trim reference preset that is calculated after you enter your weights, flap setting and CG on the PERF Init pages is only a starting point. That setting is valid for rotation and liftoff, but once the aircraft is airborne, the pilot will have to manually and continuously adjust the trim to relieve pressure on the yoke as the aircraft accelerates. If you watch any YT cockpit video of an Boeing airliner takeoff, you will see the pilot making continuous brief adjustments of the yoke trim switch during climb. 

The fly by wire system on an Airbus is different in this regard.

Once established in climb, let go of the joystick or yoke completely and see what the pitch does. Does it stay put, or does the nose want to rise or drop? Typically it will drop, meaning you need more nose-up trim. What you want to achieve is the ability to let go of the yoke with the aircraft holding pitch attitude by itself, which is an indication that the elevators are at neutral.

Again, if your joystick has no centering spring, being able to trim by feel may be very difficult, in which case you may have to de-select the realistic autopilot engagement option in the PMDG options menu. I know you don’t want to do that, but with no spring in the joystick or yoke to provide a degree of trim feedback, it may be the only way to  get the AP to engage reliably.

Once the autopilot is engaged, it will automatically control pitch trim itself, but you need to be in trim initially to get the autopilot to connect.

Share this post


Link to post
Share on other sites
2 hours ago, JRBarrett said:

Again, if your joystick has no centering spring, being able to trim by feel may be very difficult, in which case you may have to de-select the realistic autopilot engagement option in the PMDG options menu. I know you don’t want to do that, but with no spring in the joystick or yoke to provide a degree of trim feedback, it may be the only way to  get the AP to engage reliably.

I agree with Jim.. I couldn't use a joystick that didn't self-center.  A student pilot learns that it is control pressure that counts, not control movement.  We fly the airplane balancing the control pressures with trim.  We never look down at the stick or yoke or trim wheel to see where it is at (except when setting takeoff trim), it is all done with feel.  A floppy stick?

Share this post


Link to post
Share on other sites
22 hours ago, Ephedrin said:

Trimming doesn‘t need tonbe mentioned in a manual, it‘s basic part of initial flight training, long before an airliner‘s FCOM comes into account. 

Yes, it needs to be mentioned, if that's part of the actual procedure. Being a basic part of the initial training does not cut it. I'm not saying that a 737 pilot doesn't use the trim after take-off, but a new comer flying the PMDG 737NGX for the first time is not going to trim the airplane if it's not mentioned in the manual. He's going to use only the technique that's mentioned in the manual.

Ken.

Share this post


Link to post
Share on other sites
On 10/6/2018 at 1:00 AM, kmanning said:

I went back and reviewed all of the manuals for this phase of flight, including the tutorials, and none of them mentions anything about trimming the aircraft during this phase of the flight. It just mentions the procedures I've just mentioned above

Yeah. Mostly because from the foundations of ever getting into airplanes, pilots are taught to re-trim as necessary. So far, you have at least three real world pilots telling you to re-trim, so...re-trim, and make sure you’re passing the plane to the AP in a manner in which it will accept it.

Something is wrong with the way you’re giving the plane to the AP. If you’ve been getting lucky up to this point, then you’ve been getting lucky. 

Share this post


Link to post
Share on other sites
15 hours ago, JRBarrett said:

I’m not clear as to whether your joystick has a centering spring to return the stick to a neutral position when you let go of it. Most do, but if yours does not, that is probably part of the problem, as it makes it difficult to “feel”when the aircraft is out of trim.

Well, it does have a return to center, but it does not use springs. Anyway, I have that turned off because the return to center action is not realistic to a real yoke in a actual aircraft. In a real aircraft, you can freely move the yoke back and forth and there's no return to center force, but that only applies when you're sitting on the ground. When you're in flight, you have aerodynamic forces acting on the control surfaces that put force on the control wheel. Therefore, the aerodynamic forces that some of you refer to are only being simulated by that return to center force. 

 

15 hours ago, JRBarrett said:

Once established in climb, let go of the joystick or yoke completely and see what the pitch does. Does it stay put, or does the nose want to rise or drop? Typically it will drop, meaning you need more nose-up trim. What you want to achieve is the ability to let go of the yoke with the aircraft holding pitch attitude by itself, which is an indication that the elevators are at neutral.

Yes, it stays on put when I have achieved guidance cues by following the flight director bars and a V2 + 20. This tells me that the airplane should be in trim. But let me mention that when I release the yoke, it is not centered because I'm in the climb. The yoke is pulled back, as it would be in the real aircraft.

15 hours ago, JRBarrett said:

Again, if your joystick has no centering spring, being able to trim by feel may be very difficult, in which case you may have to de-select the realistic autopilot engagement option in the PMDG options menu. I know you don’t want to do that, but with no spring in the joystick or yoke to provide a degree of trim feedback, it may be the only way to  get the AP to engage reliably.

Yes, that's true that I cannot feel if the plane is in trim, but I could look at the PFD flight director bar and that should give me some cue as to how much to trim. If I continue to have issues with the auto-pilot not engaging, I'll just turn the return to center position back on so that I can feel the trim. But I've always used the flight director bars as a guidance as suggested in the manual.

Ken.

Share this post


Link to post
Share on other sites

don't  know  if  you have  done  this,  have  you  tried   disconnecting  your  stick to see if  you have  the  same  issues 

Share this post


Link to post
Share on other sites
2 hours ago, kmanning said:

Yes, it needs to be mentioned, if that's part of the actual procedure. Being a basic part of the initial training does not cut it. I'm not saying that a 737 pilot doesn't use the trim after take-off, but a new comer flying the PMDG 737NGX for the first time is not going to trim the airplane if it's not mentioned in the manual. He's going to use only the technique that's mentioned in the manual.

So by that logic, you need the manual to tell you that you need to release the parking brakes in order to be able to taxi the plane?

1 hour ago, kmanning said:

Well, it does have a return to center, but it does not use springs. Anyway, I have that turned off because the return to center action is not realistic to a real yoke in a actual aircraft. In a real aircraft, you can freely move the yoke back and forth and there's no return to center force, but that only applies when you're sitting on the ground. When you're in flight, you have aerodynamic forces acting on the control surfaces that put force on the control wheel. Therefore, the aerodynamic forces that some of you refer to are only being simulated by that return to center force. 

 

1 hour ago, kmanning said:

Yes, it stays on put when I have achieved guidance cues by following the flight director bars and a V2 + 20. This tells me that the airplane should be in trim. But let me mention that when I release the yoke, it is not centered because I'm in the climb. The yoke is pulled back, as it would be in the real aircraft.

This sounds like your problem. On the actual aircraft, you would be in trim if you're able to maintain your desired pitch with the yoke centered, but if you turned off return to center, you wouldn't have any idea if your yoke was centered or not. In other words, if your yoke is pulled back as you just described, you are NOT in trim, hence autopilot not engaging. The whole idea of trim is so you don't have to have the yoke pulled back during the climb since on the actual 747, that's a lot of force you're having to apply to the yoke just holding it back.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now