When NOT to use the TO/GA buttons

[Evan]

This one is for the pros here. We have seen a recent fatal incident, and a number of others in the past, where pilots have initiated a go-around without using the TO/GA buttons despite procedural recommendations or requirements to do so. I don't see a downside to using them, especially if you can keep one autopilot engaged but even without A/P use of the buttons should prevent the thrust/pitch coupling issues from leading to stall warnings, spatial disorientation and/or over control in IMC. My question is: is there a go-around scenario where you would not want to use them? Or is this just bad piloting?

[Gabriel]

without A/P use of the buttons should avoid the thrust/pitch coupling issues

How?

[Evan]

How?

Well, as I understand it, using the TO/GA function (pushing the button once) will result in N1 levels calculated to achieve a 1000-2000fpm climb rather than the excessive underslung panic power trip we are seeing in these manual thrust incidents. It also prevents the FD's from attempting to stay on ILS and assures that they are directing you with go-around in mind, thus minimizing the disorientation and tendency to over control or fight the STS pitch trim functions. …as I understand it. But the question remains: is there a scenario where the GA button is detrimental. I'm trying to understand the reason why it is not used in these situations that end so tragically.

[3WE]

I'm cuing the fundamental airmanship comments...

Like: Maintain healthy attitudes, airspeeds and power settings...

...just like you do any other time you are hand flying.

My understanding of the TOGA button is that it optimizes performance so you can clear the proverbial 20-decker, fully-loaded school bus of nuns that wanders across a midfield turnoff just as you cross the threshold (or the 5000 ft cliff just off the departure end.)

A parlour talker might ague that it wasn't neccesary if you simply need to do a fat, dumb and lazy transition from a descent to a climb...or that with a little attention, a well trained pilot might acheive 95% of maximum performance and maybe only take out the top deck of the bus....

[Gabriel]

Well, as I understand it, using the TO/GA function (pushing the button once) will result in N1 levels calculated to achieve a 1000-2000fpm climb rather than the excessive underslung panic power trip we are seeing in these manual thrust incidents. It also prevents the FD's from attempting to stay on ILS and assures that they are directing you with go-around in mind, thus minimizing the disorientation and tendency to over control or fight the STS pitch trim functions. …as I understand it. But the question remains: is there a scenario where the GA button is detrimental. I'm trying to understand the reason why it is not used in these situations that end so tragically.

I agree with everything regarding the FD. If you don't use the TO/GA function you better re-configure the flight guidance system manually or directly turn the FD off. The FD is a great tool when it has the same goal than the pilots. If not, it's an enemy.

If you see the part that I quoted in the previous post, my question was specifically about the thrust/pitch coupling.

The first thing that I'd like to say is that "excessive underslung panic power trip" is a bit of an exaggeration. Even if the thrust line went through the CG, passing from a negative excess thrust to a high positive one will make the plane increase it's speed past its trim speed and at a fast rate, and because the positive speed stability the plane will pitch up by itself, overshoot the "equilibrium" pitch and keep pitching up until the speed starts to diminish and then will still pitch up until the speed has decreased down to the trim speed again. Only at this point it will start to pitch down again, but at this point it will be quite above the pitch needed to keep the trim speed so the speed will keep decaying at a fast rate (almost as fast as it increased when thrust was added) and so on... the famous (?) long-period longitudinal oscillation mode a.k.a phugoid. The "underslung" thrust line will just add a bit more of pitch-up moment that has the effect of making the plane pitch up a bit faster and reduce the trim speed so the plane will pitch up a bit more than if the thrust passed through the CG.

Now, all that is true only if the plane is left alone after adding tthrust. Pilots know this instinctively but they are typically not consciously aware of it: Their main function when handling the elevator is to control the AoA to a) adjust the trim speed and b) damp the phugoid. To do that the pilot first pulls up to pitch up faster than if the plane was left alone and then push down to prevent the plane from pitching up past the target pitch. Then he will make small adjustments in pitch to hold the speed at the target go-around speed, which is typically faster than the trim speed that it was following during the approach.

In my little experience in a 737 simulator, the effect of the undesrlung engines remains hidden for the pilot during a go-around. I don't say that it's negligible. I don't think it is. But you add thrust and the plane will try to speed up and pitch up and the job of the pilot is to pitch up faster first and then prevent overshooting the target pitch, underslung engines or not. So what the plane tends to do is basically the same and the pilot's actions are basically the same, and the pilot cannot tell how much of that is due to the natural aerodynamic response of the plane and how much is due to the underslung engines.

I'd like very much to hear from VNav, who has flown both the 737 and the MD80, to see if there is something intrinsically different in what the planes do and what the pilot has to do during a manual go-around. My bet? Yes, different planes, different feel, different moods. But nothing significant that can be directly attributed to the underslung engines.

Now, the TO/GA adds trhust for 1000/2000 fpm... Well' I think I0ve heard it somewhere, in some planes. But not all.

For example, the Airbus don't have TOGA buttons and the method to trasnsition to approach to go-around is to move the throttles to TOGA. This will reconfigure the airplane systems and the FD for the G/A. In fact, pilots devised a method called "TOGA tap" where, when full thrust is not needed, they move the throttles to TOGA (to reconfigure) and immediately back to climb to set a more moderate thrust. This nearly caused an accident when the pilot thought that he had done the "TOGA tap" but in fact he did the "almost TOGA tap", so the plane never configured for TOGA and then the pilot found himself fighting the airplane systems who had a different objective than him. (I don't remember the details).

Based on my experience with the MSFS and a very good add-on of the MD-80, the TOGA buttons there will set TOGA thrust (if the AT is on), the pitch mode of the flight director will change from G/S track to speed (equivalent to FLTCH) which the AP will follow if engaged, and the heading mode will change from LOC to hold current heading.

I don't why one would not use the TOGA mode, mainly to prevent having to manually reconfigure the systems for go-around. But I also don't see how not doing it could have been a significant factor in the Russian crash. The flight director, even of still in approach mode, would have been commanding nose-up when the pitch went below 10° nose down or the sink rate past 1500fpm or something.

[Evan]

I agree with everything regarding the FD. If you don't use the TO/GA function you better re-configure the flight guidance system manually or directly turn the FD off. The FD is a great tool when it has the same goal than the pilots. If not, it's an enemy.

If you see the part that I quoted in the previous post, my question was specifically about the thrust/pitch coupling.

The first thing that I'd like to say is that "excessive underslung panic power trip" is a bit of an exaggeration. Even if the thrust line went through the CG, passing from a negative excess thrust to a high positive one will make the plane increase it's speed past its trim speed and at a fast rate, and because the positive speed stability the plane will pitch up by itself, overshoot the "equilibrium" pitch and keep pitching up until the speed starts to diminish and then will still pitch up until the speed has decreased down to the trim speed again. Only at this point it will start to pitch down again, but at this point it will be quite above the pitch needed to keep the trim speed so the speed will keep decaying at a fast rate (almost as fast as it increased when thrust was added) and so on... the famous (?) long-period longitudinal oscillation mode a.k.a phugoid. The "underslung" thrust line will just add a bit more of pitch-up moment that has the effect of making the plane pitch up a bit faster and reduce the trim speed so the plane will pitch up a bit more than if the thrust passed through the CG.

Now, all that is true only if the plane is left alone after adding tthrust. Pilots know this instinctively but they are typically not consciously aware of it: Their main function when handling the elevator is to control the AoA to a) adjust the trim speed and b) damp the phugoid. To do that the pilot first pulls up to pitch up faster than if the plane was left alone and then push down to prevent the plane from pitching up past the target pitch. Then he will make small adjustments in pitch to hold the speed at the target go-around speed, which is typically faster than the trim speed that it was following during the approach.

In my little experience in a 737 simulator, the effect of the undesrlung engines remains hidden for the pilot during a go-around. I don't say that it's negligible. I don't think it is. But you add thrust and the plane will try to speed up and pitch up and the job of the pilot is to pitch up faster first and then prevent overshooting the target pitch, underslung engines or not. So what the plane tends to do is basically the same and the pilot's actions are basically the same, and the pilot cannot tell how much of that is due to the natural aerodynamic response of the plane and how much is due to the underslung engines.

I'd like very much to hear from VNav, who has flown both the 737 and the MD80, to see if there is something intrinsically different in what the planes do and what the pilot has to do during a manual go-around. My bet? Yes, different planes, different feel, different moods. But nothing significant that can be directly attributed to the underslung engines.

Now, the TO/GA adds trhust for 1000/2000 fpm... Well' I think I0ve heard it somewhere, in some planes. But not all.

For example, the Airbus don't have TOGA buttons and the method to trasnsition to approach to go-around is to move the throttles to TOGA. This will reconfigure the airplane systems and the FD for the G/A. In fact, pilots devised a method called "TOGA tap" where, when full thrust is not needed, they move the throttles to TOGA (to reconfigure) and immediately back to climb to set a more moderate thrust. This nearly caused an accident when the pilot thought that he had done the "TOGA tap" but in fact he did the "almost TOGA tap", so the plane never configured for TOGA and then the pilot found himself fighting the airplane systems who had a different objective than him. (I don't remember the details).

Based on my experience with the MSFS and a very good add-on of the MD-80, the TOGA buttons there will set TOGA thrust (if the AT is on), the pitch mode of the flight director will change from G/S track to speed (equivalent to FLTCH) which the AP will follow if engaged, and the heading mode will change from LOC to hold current heading.

I don't why one would not use the TOGA mode, mainly to prevent having to manually reconfigure the systems for go-around. But I also don't see how not doing it could have been a significant factor in the Russian crash. The flight director, even of still in approach mode, would have been commanding nose-up when the pitch went below 10° nose down or the sink rate past 1500fpm or something.

I understand everything you said there (I should have titled this thread TO/GA button/detent I suppose) although the report on the Russian 737 crash gave me the impression that the rapid rise in pitch was largely due to thrust and flap retraction and the pilots failure to counter it. That last part is what concerns me because from time to time pilots will fail to do this. My impression (perhaps false) is that the TO/GA mode will apply the necessary thrust to achieve the guidance targets but nothing in excess of that. Perhaps with less pitch-coupling effect from thrust. (I also wonder if the wing forward orientation and higher power of the 'classic' and NG engines exacerbates the effect). And no, I'm not suggesting that TO/GA relieves the pilots from flying the plane, I'm just thinking in degrees of safety here.

But what really concerns me here is guidance. It seems the Somographic/ Somatogyral illusion factor and just general disorientation in IMC is also playing a major role. It seems to happen when the GA is improvised in manual flight. Flight training teaches pilots to be ahead of it and to be mentally prepared for GA but obviously every tree has it's low hanging fruit and every pilot can have a bad day I suppose. The nav functions of TO/GA alone seem to make it necessary if we are to avoid such incidents. If your Sichuan A319 pilots had selected TO/GA thrust at the low speed warning and had GA/TRK and SRS modes I dare think they would not have gotten into the mess they did. Your 'TOGA Tap' mess-up illustrates the danger or not having the nav and speed modes working with you (also situational awareness in that case).

So, it seems obvious to me WHY you WOULD use the button or the detent. (TO/GA Tap also illustrates the need to get the guidance first before manually adjusting power). What I'm wondering here is if there is a valid reason why some pilots are not using them or it is just a bad CRM / ignorance of procedure thing / stick and rudder bravado thing?

[MCM]

Are we talking in manual or automatic flight?

The TOGA Tap actually gives you the prime reason... Excessive thrust control.

There's a couple of reasons why you might be loathed to use the G/A, and it does vary based on the plane you are flying and the way the autoflight system works.

In an aeroplane that does not apply thrust for say 2000fpm climb (which is a lot still), full thrust application can be a handful and create 'unacceptable' pitch attitudes and rates of climb. A light 767 can get over 6000 fpm at go around thrust, and if you've only got 1000ft to climb, then good luck with that one! If you are hand flying, which on the 767 is usually done with the autothrottle not engaged, pressing GA will engage the a/t and give you all the power, which is far more than you need, and can create problems trying to prevent flap over speeds while hanging on for dear life. Significant nose down yoke and forward trim are required in a short space of time to prevent a level bust.

Remember you're probably going from something in the vicinity of 1 deg nose up, to 20, then back down to a couple, all within 30 seconds? While trying to manage an acceleration and flap retraction.

Another reason is certain aeroplanes, when reaching low fuel states, require you to limit pitch attitude to prevent fuel supply problems.

A slightly more unusual one that needs forethought is the descending go around.

I'm not advocating not pressing GA, but there are certainly reasons to think about it.

[Evan]

Are we talking in manual or automatic flight?

The TOGA Tap actually gives you the prime reason... Excessive thrust control.

There's a couple of reasons why you might be loathed to use the G/A, and it does vary based on the plane you are flying and the way the autoflight system works.

In an aeroplane that does not apply thrust for say 2000fpm climb (which is a lot still), full thrust application can be a handful and create 'unacceptable' pitch attitudes and rates of climb. A light 767 can get over 6000 fpm at go around thrust, and if you've only got 1000ft to climb, then good luck with that one! If you are hand flying, which on the 767 is usually done with the autothrottle not engaged, pressing GA will engage the a/t and give you all the power, which is far more than you need, and can create problems trying to prevent flap over speeds while hanging on for dear life. Significant nose down yoke and forward trim are required in a short space of time to prevent a level bust.

Remember you're probably going from something in the vicinity of 1 deg nose up, to 20, then back down to a couple, all within 30 seconds? While trying to manage an acceleration and flap retraction.

Another reason is certain aeroplanes, when reaching low fuel states, require you to limit pitch attitude to prevent fuel supply problems.

A slightly more unusual one that needs forethought is the descending go around.

I'm not advocating not pressing GA, but there are certainly reasons to think about it.

MCM, what about the FD and guidance issues? The problem leading to loss of control seems to be as much about disorientation as it does pitch excursions.

[3WE]

...The problem leading to loss of control seems to be as much about disorientation as it does pitch excursions...

As in fundamental airmanship?

[MCM]

I'm not sure what you're getting at Evan. I simply answered your question - reasons why pilots might be reluctant to hit the GA switches.

I'm not saying that you shouldn't press them in these scenarios. Just that, like anything, you need to make the aeroplane do what you want it to, which may not be 'balls to the wall' thrust.

If you choose not to press the button, then you have to be cognisant of the modes you are in, and change them to appropriate modes.

For example, passing through 1800 ft the ILS, ATC instruct you to go around and maintain 2000ft. Is pressing GA appropriate here? Not all go arounds are created equal. How about passing 2300 ft and you are told to do a descending go around?

That said, in the vast majority of cases, GA is the appropriate mode to be using.

[Gabriel]

A question MCM.

I guess that the first part of a go-around is a very high workload time. If you are hand flying, maybe it's not the best time to divert your attention from the basics of flying the airplane to reconfigure the flight guidance system so as the flight director shows you what you already know must be done to accomplish your goal.

Would it be appropriate to initially switch the F/D off so it doesn't distract you with spurious cues (like trying to bring you back to the glide slope or aim for a high performance go-around) and instead fly the basic six-pack way? And only when you are stabilized and the workload reduced to a more reasonable level start reconfiguring the FGS and re-engage the FD (and maybe the AP)?

It looks to me (and I can be totally wrong) that, for some reason, airliners' pilots tend to be quite reluctant to switch off the FD, as if they had become too used to follow the FD cues instead of interpreting what pitch is needed and go for it without something telling you how much to pull up.

[Evan]

I'm not sure what you're getting at Evan. I simply answered your question - reasons why pilots might be reluctant to hit the GA switches.

I'm not saying that you shouldn't press them in these scenarios. Just that, like anything, you need to make the aeroplane do what you want it to, which may not be 'balls to the wall' thrust.

If you choose not to press the button, then you have to be cognisant of the modes you are in, and change them to appropriate modes.

For example, passing through 1800 ft the ILS, ATC instruct you to go around and maintain 2000ft. Is pressing GA appropriate here? Not all go arounds are created equal. How about passing 2300 ft and you are told to do a descending go around?

That said, in the vast majority of cases, GA is the appropriate mode to be using.

MCM, I'm wondering, do you see anything in the recent Russian 737 crash that would fit the above criteria?

[MCM]

I haven't really been following it that closely to be honest, so I can't really give you an answer to that Evan. I lost attention when the thread was all about poor Russian maintenance standards. Instrument misinterpretation, loss of SA due to the manoeuvring, or mechanical all seemed to be viable. A mishandled go around also seemed a possibility, but I really don't know anything other than what I in the first page or two of that thread.

As to switching the F/D off, it's not that hard to 'look through' it if required initially. But yes, if its not giving you useful information then it should be off.

In the vast majority of cases, you are pressing GA and so you are getting useful information from it.

[jarod]

I have been told that TO/GA must always be used during a go-around procedure. If you want to make a go arund what would be the purpose to do not use it ?

[EconomyClass]

The first thing that I'd like to say is that "excessive underslung panic power trip" is a bit of an exaggeration.

Sounds like the title to a Bob Dylan song. I love phrases like that.