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Deslect vs Disconnect Autothrottle (Arm mode and Go Around)

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Hello everyone,

Correct me if I'm wrong simmers. It's stated in different professional forums that turning Autothrottle off when on final can be done in 2 different ways:

1- "Deselect": done by pressing the buttons situated at the thrust levers. In this case, the thrust is manual but the thrust mode announciates "Arm" and the A/T is armed so it engages automatically for alphafloor protection or by pressing the TOGA switches in the case of a go around.
2- "Disconnect": done by turning off the A/T switch on the MCP. It's full manual thrust without "Arm" mode or speed protection and in case of a go around, the thrust can only be set manually.

When I (only) deselect in the NGX, there is no Arm mode and I can't get TOGA thrust (I get only TOGA mode annunciated in the vertical mode) when I press the TOGA switches for a go around.

Any clarifications on this please? Thank you!

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You can "deselect" by pressing the MCP SPEED button and enter the ARM mode. You can disconnect via the buttons on the sides of the thrust levers.

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You can "deselect" by pressing the MCP SPEED button and enter the ARM mode. You can disconnect via the buttons on the sides of the thrust levers.

 

Our operating manual specifically prohibits us from doing this.  I don't know the exact reasoning behind it but I'm guessing they have a good reason, whatever it may be.

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Our operating manual specifically prohibits us from doing this.  I don't know the exact reasoning behind it but I'm guessing they have a good reason, whatever it may be.

 

I thought you were at AA. AA is the only airline I'm familiar with the uses ARM on the 737.The FCTM has a section on why not to do this (pitch coupling, or some such) but of course the airlines and the POI have the final word.

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Probably to make sure the A/T is on managing speed until committed to land. The way Matt says is the only one to leave the door open for a TOGA in case, but you are on your own for speed management for the rest of the way.

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I thought you were at AA. AA is the only airline I'm familiar with the uses ARM on the 737.The FCTM has a section on why not to do this (pitch coupling, or some such) but of course the airlines and the POI have the final word.

 

I am with AA.  I should have been more specific.  It's not authorized to deselect the MCP SPD with the speed switch on the MCP on approach.  On approach the autothrottles can be engaged or disengaged, but you can't leave the autothrottle armed if you aren't using them.  It's normal to leave autothrottle engaged until you touch down but you shouldn't be seeing them in ARM during the approach phase.

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I remember reading a piece where Boeing recommends A/T used whenever A/P is engaged--coupled. If the autopilot is disconnected then the A/T should also be disconnected.

 

Supposedly the A/T's reliability is brought into question when one hand flies instead of having the A/P on. This especially when there are wind gusts during the approach and there are power corrections out of sync with the hand flown inputs. (pitch coupling).

 

Ah I don't know I am not a pro like you guys, just what I read.

 

Edited to add: I found the piece. I had replied to a similar thread a while back. This repeats recommendations by Boeing and states differences in airline policy.

 

http://www.flaps2approach.com/journal/2014/9/2/b737-autothrottle-at-normal-and-non-normal-operations.html

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I am with AA.  I should have been more specific.  It's not authorized to deselect the MCP SPD with the speed switch on the MCP on approach.  On approach the autothrottles can be engaged or disengaged, but you can't leave the autothrottle armed if you aren't using them.  It's normal to leave autothrottle engaged until you touch down but you shouldn't be seeing them in ARM during the approach phase.

 

Oh, that's right. Not ARM but A/T all the way down.

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Joe and Matt, I'm particularly interested to hear how RW pilots setup to land. I've been wondering about the setup for landing for awhile now - I've been looking around the internet for answers, but its the internet and  who knows what the real source is when you find a procedure anywhere on here. Seeing as how you two are legit, what a resource for this question. 

To the OP, I read your original thoughts about putting the AT into ARM and its made complete sense to me to put the AT into ARM on approach as opposed to reaching up and flipping the AT switch down on approach (just before turning off the AP as well). So in that last few thousand feet of approach I'm off all automation. The problem was in the event of a go around, everything is manual, so I have to pitch up, throttle up, stay on the published missed approach, pull the flaps back, and work the radios. Since it very rarely happens, if / when it does happen I usually screw something up like pitch to high or roam off the missed approach or something.

 

To me it seems putting the AT into ARM and having the speed dialed up so that in the event of a missed approach I could simply click the TOGA at least the throttles would be off that list of things to deal with.

 

But then you say putting it into ARM is bad.... and then you say AT all the way down....

 

My question for you both is ... well what do you do on your approaches? Do you just leave on the AT up till touchdown (hands off the throttles) even with the AP disengaged? Or do you go into full manual and deal with everything manually on the announcement of a go around (you have help from the FO which I do not have that luxury in the sim). 

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My question for you both is ... well what do you do on your approaches? Do you just leave on the AT up till touchdown (hands off the throttles) even with the AP disengaged? Or do you go into full manual and deal with everything manually on the announcement of a go around (you have help from the FO which I do not have that luxury in the sim).

 

My technique:

 

Autothrottle stays engaged until touchdown.  Hand on the throttles and actively controlling the airspeed.  I typically end up adding or reducing power in advance of the autothrottle as I can see the need for power changes before it can.  What effectively ends up happening is my hand on the throttles ends up being a stabilizing effect, dampening out the add/reduce power cycles the autothrottle would otherwise do.  Hands off the throttles would be a big no-no. 

 

Autopilot use depends on the type of approach being flown, the weather, and the runway.  Unless otherwise required I typically disconnect the autopilot once I am fully configured for landing.

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It's worth nothing that my technique does not carry over into the sim as well due to differences in the autothrottle retard logic in the sim vs. the real airplane. In The NGX I find it necessary to disengage the autothrottle prior to touchdown on anything other than an ILS approach.

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does not carry over into the sim as well due to differences in the autothrottle retard logic in the sim vs. the real airplane

 

I was about to say that... curious in the real thing there must be internal motors and gears pushing the levers up and down, but obviously you must be able to override by applying pressure with your hands. Makes me wonder ... for example ... if you pushed the levers forward above what the AT and gearing mechanism has it set at, your speed would likely go up which in turn I would expect the mechanism to retard further. Do the throttles give you more resistance the further you override the levers away from the computer / mechanisms desired position? What happens if you let go, does it spring back to the A/T position?

 

In the sim (as you mention) the thrust will not change I believe unless its in ARM. Correct me if I'm wrong (I haven't tried this)  but so long as the AT is engaged you can push up and down on the throttles all you want but it will have no effect.

 

So Joe, if in the NGX, and you were flying in manually with the AT off (like I do), what would you do if you are told to go around at around 200'? What would your procedure be in the sim knowing its not what you do in the real cockpit?

 

Knowing that ARM is a no no in the RW... but considering in the sim ARM is possible and logically a way to work around the fact that in the sim your inputs will override the AT while still having the AT on and available for a go around single button push maybe the OP's deselect method is the way to go in the NGX.

 

Example, deselect the speed on approach while having the AT still on the AT goes into ARM mode... so you have full manual control of the throttles on the way in. If instructed to go around, I press TO/GA and the AT springs into action and I can take my hands off the throttles freeing a hand up to pull the flaps back, pull the gear up, and get the pitch right and begin re configuring...  

 

 

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I was about to say that... curious in the real thing there must be internal motors and gears pushing the levers up and down, but obviously you must be able to override by applying pressure with your hands. Makes me wonder ... for example ... if you pushed the levers forward above what the AT and gearing mechanism has it set at, your speed would likely go up which in turn I would expect the mechanism to retard further. Do the throttles give you more resistance the further you override the levers away from the computer / mechanisms desired position? What happens if you let go, does it spring back to the A/T position?

 

There is a clutch in the servo mechanism that drives the throttle levers.  You can override the autothrottle by pushing or pulling the levers.  There is some resistance, but not a lot.  If you override it and let go of the levers the autothrottle will return them to wherever it wants them to be.


 

 


So Joe, if in the NGX, and you were flying in manually with the AT off (like I do), what would you do if you are told to go around at around 200'? What would your procedure be in the sim knowing its not what you do in the real cockpit?

 

Just press TOGA and push the throttles to go around power.  When you have the airplane under control simply re-engage the autothrottle if you so desire.  In the airplane it's easier, just push the power up to approximately GA power and call for the pilot monitoring to set GA power.  When you are ready for the autothrottle back call for the PM to engage it.

 

In the sim I mapped a button on my stick to control the A/T arm switch.  It helps compensate for the lack of the second pilot.


 

 


Knowing that ARM is a no no in the RW... but considering in the sim ARM is possible and logically a way to work around the fact that in the sim your inputs will override the AT while still having the AT on and available for a go around single button push maybe the OP's deselect method is the way to go in the NGX.

Example, deselect the speed on approach while having the AT still on the AT goes into ARM mode... so you have full manual control of the throttles on the way in. If instructed to go around, I press TO/GA and the AT springs into action and I can take my hands off the throttles freeing a hand up to pull the flaps back, pull the gear up, and get the pitch right and begin re configuring...

 

Perhaps.  A go-around without the autothrottle isn't a big deal, you just have to push the levers up manually.  Don't overthink it.

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Joe and Matt, I'm particularly interested to hear how RW pilots setup to land. I've been wondering about the setup for landing for awhile now - I've been looking around the internet for answers, but its the internet and  who knows what the real source is when you find a procedure anywhere on here. Seeing as how you two are legit, what a resource for this question. 

 

To the OP, I read your original thoughts about putting the AT into ARM and its made complete sense to me to put the AT into ARM on approach as opposed to reaching up and flipping the AT switch down on approach (just before turning off the AP as well). So in that last few thousand feet of approach I'm off all automation. The problem was in the event of a go around, everything is manual, so I have to pitch up, throttle up, stay on the published missed approach, pull the flaps back, and work the radios. Since it very rarely happens, if / when it does happen I usually screw something up like pitch to high or roam off the missed approach or something.

 

To me it seems putting the AT into ARM and having the speed dialed up so that in the event of a missed approach I could simply click the TOGA at least the throttles would be off that list of things to deal with.

 

But then you say putting it into ARM is bad.... and then you say AT all the way down....

 

My question for you both is ... well what do you do on your approaches? Do you just leave on the AT up till touchdown (hands off the throttles) even with the AP disengaged? Or do you go into full manual and deal with everything manually on the announcement of a go around (you have help from the FO which I do not have that luxury in the sim). 

 

I try to get the automation (both A/P and A/T) off as early as I can. They both come off at the same time. If things are busy, I'll delay the disconnect. Things like a busy environment make me delay the disconnect. If I'm up in Alaska, and it's a beautiful day, it'd be a shame not to disconnect.

 

To me it's a balancing act between maintaining manual flying skills vs. using the benefits of automation.

 

Also, RW the autopilot can do a great job of handling turbulence. I don't think the A/T is as good at handling windshear.

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Hello everyone,

 

Correct me if I'm wrong simmers. It's stated in different professional forums that turning Autothrottle off when on final can be done in 2 different ways:

 

1- "Deselect": done by pressing the buttons situated at the thrust levers. In this case, the thrust is manual but the thrust mode announciates "Arm" and the A/T is armed so it engages automatically for alphafloor protection or by pressing the TOGA switches in the case of a go around.

2- "Disconnect": done by turning off the A/T switch on the MCP. It's full manual thrust without "Arm" mode or speed protection and in case of a go around, the thrust can only be set manually.

 

When I (only) deselect in the NGX, there is no Arm mode and I can't get TOGA thrust (I get only TOGA mode annunciated in the vertical mode) when I press the TOGA switches for a go around.

 

Any clarifications on this please? Thank you!

 

Sorry I didn't respond sooner in the other forum post!

 

Pushing either A/T Disconnect on the Thrust Lever or pushing down the A/T switch has the same affect and it does exactly what it says on the tin! It will disconnect the A/T and the thrust mode annunciation will go blank, you have full control of the Thrust.

 

I've personally never disconnected the A/T using the switch, only on the thrust lever as you have to take your hand off the thrust lever to turn it off.

 

Looks like the other guys have covered the rest! 

 

 

I thought you were at AA. AA is the only airline I'm familiar with the uses ARM on the 737.The FCTM has a section on why not to do this (pitch coupling, or some such) but of course the airlines and the POI have the final word.

 

That's a new one re using ARM I've heard! Is the A/T engaged all the way until touchdown? I've read about some interesting quirks used with loads of different operators it if it works it works. On final we disconnect A/T and A/P simultaneously and the PF has full control over thrust. 

 

In gusty, high wind conditions the A/T has a hard time on Final maintaining speed and 

 

 

Also, RW the autopilot can do a great job of handling turbulence. I don't think the A/T is as good at handling windshear.

 

The A/T is ruddy useless in gusty, high wind conditions! It has a hard time on Final maintaining speed and you always have to override it. 

 

Out of curiosity Matt and Joe how do you guys deal with Windshear Escape in AA? We recently changed our procedure. We use to disconnect the A/T immediately but we now.

 

1. PUSH TO/GA

2. MAX THRUST

3. DISCONNECT A/T 

 

etc etc....

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