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When to disconnect auto throttle before landing

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In the real airplane it takes very little force to override the A/T servos.  On approach I am still actively controlling the thrust even though the A/T is on, especially on the gusty days.

 

We don't have to use the A/T to touchdown but almost everyone I fly with does.  I like it because it allows the use of VREF+5 for every approach regardless of winds and if you need to go around the A/T is already engaged when you press TOGA.  There really isn't a down side to using it.


 

 


I was under the impression that in the 737 the advice from Boeing (and certainly SOP at a Big Airline here, and a large Irish one as well as far as I know) is 'all out, or all in'. In other words, if you take the A/P out you should also take the A/T out, mainly because you may end up with undesirable oscillations in pitch due to the effect of the underslung engines and the delay between, for example, your manual pitch input and the reaction of the A/T. Likewise, I'd always heard A/T off first, then A/P. Certainly the case for the non-FBW Boeings I'm familiar with: i.e. 737/747/757/767.



The FBW in the 777 (and I presume the 787) compensates for the thrust/pitch couple (and I suspect the A/T software is improved), therefore A/T to touchdown is recommended and regularly used. Same of course in the Airbuses.

 

I honestly don't notice much difference between hand flown approaches with the A/T on vs. A/T off.  I'm proactively adjusting the thrust ahead of the A/T anyway so correcting for the pitch/thrust coupling isn't any different from an approach flown with the A/T off.  Your hand is on the thrust levers so you are in the loop with what the power is doing.

 

 

 


Interesting to hear that Joe's operator allows & encourages use of A/T to touchdown whilst hand-flying!

 

To put this in perspective it's not a small operator of 737s, it's the biggest airline in the world (big subtle hint!).  Our 737 program is pretty progressive.  It's evolved quite a bit over the years and it's very good at allowing us to take advantage of the abilities of the airplane.


Joe Diamond

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That's "could" be Delta then when doing a google.  :wink:

 

Joe,

I really enjoy reading from real pilots and enjoyed reading your post above. 

 

Its sounds like and forgive me if I misunderstand what your saying.

 

Your on AT but your controlling the trust manually(be it small amounts) at your own desecration, so the throttle system is still on AT but your overriding it as you see fit without it kicking AT off.

 

 

Is that right?

 

Sadly Something within the sim we cannot do.


David Murden.  P3D v4.5  FSL A320 A319 : PMDG NGu / 748PMDG NG / 747-/ 777 : QW 787 :  Maddog MD-80 :Q400 :   DCS: AV-8B Harrier: :  F-14B Tomcat  : F-16C Viper F/A-18C Hornet 

My FSL Walkthrough PDF From GPU to Parked.     My PMDG NG SpotLight Profile/Mod.

PC 4790k@4.6 : 1070 : 16GB DDR3 RAM : Thrustmaster Warthog HOTAS: Thrustmaster TPR.

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Sadly Something within the sim we cannot do.

 

You can, but you also can't...

 

You can, because you have the option of "A/T MANUAL OVERRIDE: ALWAYS."

You can't, because you probably don't have servo-driven hardware to drive the throttles to where the A/T wants them when you let go.


Kyle Rodgers

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That's "could" be Delta then when doing a google.

 

Bigger than Delta :)

 

 

 


Your on AT but your controlling the trust manually(be it small amounts) at your own desecration, so the throttle system is still on AT but your overriding it as you see fit without it kicking AT off.

Is that right?

 

That is correct.  I can spot trends quicker than it can and will lead it with the thrust changes.  Approaching the flare it will go into retard mode at 27' RA which may or may not work depending on the flaps setting.  On a 30 flap landing I'll usually keep the power in just a bit longer than the A/T would, a little more with flaps 40, a little less with flaps 15.


 

 


Sadly Something within the sim we cannot do.

 

Like Kyle said you need the servos to drive the thrust levers.  In the airplane if you override the A/T the levers will return to where the A/T wants them when you remove the overriding force. 


Joe Diamond

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I'm not a real pilot so, as long as FSX is concerned depends on the Developer/Aircraft.

Most of my Jets A/T off, adjust power, A/P off except Aerosoft Airbus (320) AXE 1.16 and sometimes Leonardo Maddog MD-80 and PMDG MD-11,  where it goes A/T to touchdown.


Sam. 

Waiting for the 64-bit PSION Flightsim for ZX-Spectrum ////

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Thanks for the reply Joe,

So given even though I have a Warthog HOTAS that's incredible accurate it has no servos. So none of the settings will replicate that, in your opinion would you say turning off AT within the sim is the best option because your description on how you judge the trends and the subtlety when to retard can be done within the sim but only ofcourse with AT off.

In your professional opinion when in the sim would you personally goto AT off?

 

As for Airline company Google gives odd results just read that AA carrys more people since they merged with US, did they?

 

I read does not meen its true Ryanair has the biggest fleet of 738 in the world but it is the only plane they use, it must be good on fuel as the owners are tight as a ducks @ss's .

 

@ Kyle

I have that set to override at Arm but the best option that I use is to show were my throttle is in relation to the NG's, so set throttle to match before turning of the AT


David Murden.  P3D v4.5  FSL A320 A319 : PMDG NGu / 748PMDG NG / 747-/ 777 : QW 787 :  Maddog MD-80 :Q400 :   DCS: AV-8B Harrier: :  F-14B Tomcat  : F-16C Viper F/A-18C Hornet 

My FSL Walkthrough PDF From GPU to Parked.     My PMDG NG SpotLight Profile/Mod.

PC 4790k@4.6 : 1070 : 16GB DDR3 RAM : Thrustmaster Warthog HOTAS: Thrustmaster TPR.

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So given even though I have a Warthog HOTAS that's incredible accurate it has no servos. So none of the settings will replicate that, in your opinion would you say turning off AT within the sim is the best option because your description on how you judge the trends and the subtlety when to retard can be done within the sim but only ofcourse with AT off.
In your professional opinion when in the sim would you personally goto AT off?

 

I have the Warthog as well, it's a great throttle and stick.

 

In the sim if I am shooting an ILS I will leave the AT engaged.  For other approaches I disengage it just prior to the flare as the AT in the sim does not reliably go into retard on anything other than an ILS.  That behavior does not match the real world but it is what it is.  One other little small detail that does not match is that in the airplane if you touch down with the AT engaged you don't get the AT disconnect light when the AT kicks off, in the sim you do, not a big deal.


Joe Diamond

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Thank you very much Joe, good to know.


David Murden.  P3D v4.5  FSL A320 A319 : PMDG NGu / 748PMDG NG / 747-/ 777 : QW 787 :  Maddog MD-80 :Q400 :   DCS: AV-8B Harrier: :  F-14B Tomcat  : F-16C Viper F/A-18C Hornet 

My FSL Walkthrough PDF From GPU to Parked.     My PMDG NG SpotLight Profile/Mod.

PC 4790k@4.6 : 1070 : 16GB DDR3 RAM : Thrustmaster Warthog HOTAS: Thrustmaster TPR.

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There is a very good reason for leaving autothrottle engaged: speed protection.

 

Yes, Boeing recommend that you should use manual throttle when flying manually, to avoid instability in pitch as has been mentioned earlier (the exception being during takeoff & initial climb, which is flown manually but with autothrottle engaged).

 

With autothrottle engaged, it will prevent speed dropping below minimum manoeuvre speed, or exceeding maximum speed for the current configuration: this protection is lost when A/T is disengaged.

 

An alternative technique is leave the A/T latched ON, but deselect SPEED on the MCP. The A/T now goes into ARMED mode & you control thrust by manually moving the thrust levers. However, should the speed reduce towards minimum manoeuvre speed during approach (or go-around), the A/T will become active again & add thrust as necessary, thus potentially saving your neck. Following a go-around, should the speed increase towards the current limiting speed, the A/T will become active & reduce thrust to avoid exceeding the current limit. I'm talking real world here, I've not tried it to see if it is modelled in the NGX.

 

Doug Boynton


Doug Boynton

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An alternative technique is leave the AT latched ON, but deselect SPEED on the MCP.

 

My company expressly prohibits this.  You can leave the A/T engaged, which most do, or you can disengage it.  What we cannot do is intentionally leave it engaged but in ARM by deselecting SPEED on the MCP.  There is a valid reason behind this but I cannot recall it at the moment.


Joe Diamond

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Well, it's down to company SOPs: some allow it, some don't.

 

Some people worry that the A/T may kick in as speed reduces in the flare: in which case you can completely disconnect the A/T at a late stage of the approach, just prior to the flare.

 

Having seen many instances of people getting slow during approach & go-around & subsequently exceeding flap limiting speeds when accelerating (when using manual throttle), I'm in favour of it.

 

 

Doug Boynton


Doug Boynton

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Well, it's down to company SOPs: some allow it, some don't.

 

They sign my paychecks so their opinion is the one that matters.  The rest are strictly advisory.  :)


Joe Diamond

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What conditions must be met for the AT to go into RETARD when it is set to maintain MCP speed while autopilot is off? I tried it in the sim (manual ILS approach, NAV1 tuned to ILS frequency) but it never retarded so I had to disconnect and retard manually in all haste. Do I have to select APP to get this function or did I miss anything else?

 

Hans Hjorth 


Hans Hjorth

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