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Leif9619

Go-Around procedure

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Hello guys,

 

firstly, I want to congratulate PMDG for this wonderful airplane.

 

Secondly, I have a little problem. I am not sure if this is a bug or just my stupidity.

 

Since I had to go around today, I noticed, that after pressing TO/GA the thrust levers increased and my A/T activated in THR mode for a 2000 FPM climb. Roll and pitch modes changed to TO/GA. That's how the FCOM 4.20.15 (PDF page 673) describes it. But despite changng the target airspeed to the actual airspeed the targed airspeed remained the same as for the approach. Then, after having engaged CMD 1 and after LNAV was activated I selected a higher speed to retract the flaps. After that, I selected FLCH at about 1300 ft AGL. Thereafter, pitch decreased slightly and climb thrust was set. The engines' thrust also decreased slightly and the aircraft had a hard time to accelerate while climbing to the missed approach altittude with about 600 FPM. I retracted the flaps according the flap retraction schedule and selected flap 1 maneuvering speed, but then the engines spooled down further and the aircraft nearly maintained level flight. I pushed the THRUST switch at about 2100 ft AGL, but nothing happend. When I selected V/S and A/T speed mode was activated the aircraft began to climb again. FCOM NP.21.53 (PDF page 147) points towards selecting FLCH at acceleration height and pushing the THRUST switch after flap retraction to the planned flap setting. Also, the FCOM says that climb thrust is set after the THRUST switch is pushed and not after FLCH is pushed.

 

What do you think? Did I do something wrong or is this normal behavior? I also recorded the scene and uploaded it on youtube: 

 

Thank you in advance!

 

Leif Gehre

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What do you think?

 

Right before the modes changed, I noticed that thrust wasn't at target. What are your hardware AT settings in the CDU menus? Additionally, I heard a few clicks before it switched into SPD + V/S. What were you hitting?

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Thank you for the quick response, 

 

I have A/T override set to NEVER. I think I had pushed the TO/GA button again before I pushed V/S.

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Hello,

 

isn't there anybody who can help me?

Shouldn't the thrust increase to the selected climb limit when pushing THR while FLCH SPD is the active pitch mode?

 

Regards,

 

Leif Gehre

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Hi Leif,

 

The THR switch is sometimes referred to as "the button that makes the wings fall off". In other words, it's a slightly confusing multi-function switch which does things you can accomplish in a more user-friendly way elsewhere, and so many adopt the view that they don't really understand it so they don't touch it ;).

 

If the THR switch stays blank when you press it, the thrust LIMIT will change to the next one down (GA to CLB or CON, CLB to CRZ etc). The actual thrust may or may not change.

 

If it lights up, the thrust levers will advance to THR REF.

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Thanks Simon,

 

this is interesting. Sice as you might have seen in the video nothing happened after I had pressed the THR switch. I found it very confusing that after I had pressed FLCH and the thrust limit changed from GA to CLB the airplane decreased pitch slightly to about 10 degrees, but the engines weren't turning at climb limit. Instead, N1 even decreased to about 83%. So the aircraft couldn't accelerate.

I did some go-arounds yesterday as well. When I pushed the THR switch the engines should have turned at climb limit, but actually nothing happened. In the video you can also see that when I selected the speed to 210 KIAS while in FLCH SPD the aircraft was still at nearly 10 degrees of pitch and the engines reduced N1 further to about 75%. The aircraft wasn't accelerating and couldn't climb as well.

I have also watched this CBT (https://youtu.be/kbPFCCwfahI?t=6m19s) and it is said that pushing THR in FLCH changes thrust to the selected clb thrust limit while in my case the speed mode should stay in THR.

 

I am not sure, but I think that there's something wrong. I can't imagine that this is normal behavior.

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it is said that pushing THR in FLCH changes thrust to the selected clb thrust limit while in my case the speed mode should stay in THR.

 

Yes. In FLCH the thrust limit should change (from GA to CLB) but the actual thrust mode will not change.

 

So if you are in THR REF (let's say you pressed the TOGA switches twice), pressing the THR switch will change the thrust limit to CLB. Since this is below the GA thrust limit, this will result in the thrust coming back to CLB.

 

Pressing the THR switch whilst in FLCH will change the limit, but (probably, unless the current thrust is above the new limit) not the actual thrust output. For what it's worth, if I was going to touch the THR switch at all I'd do it after levelling off at the missed approach altitude - there's not really any need to change the thrust limit whilst you are in THR.

 

Either way, I agree with you that the behaviour you are experiencing is incorrect -- the thrust limit should stay at GA when you select FLCH.

 

Incidentally, strictly speaking the sequence should be to press FLCH then SPD (the press of the SPD button will not normally have any effect -- it is just in case the aircraft has captured the missed approach altitude whilst still in TOGA which will result in the speed running away) but this should not have any impact on what you are seeing.

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Ahhhh, ok. Thank you for clarifying. I seem to have misunderstood the part with the climb limit. 

 

 

 


Incidentally, strictly speaking the sequence should be to press FLCH then SPD (the press of the SPD button will not normally have any effect -- it is just in case the aircraft has captured the missed approach altitude whilst still in TOGA which will result in the speed running away) but this should not have any impact on what you are seeing.

 

Shouldn't the SPD mode engage automatically when the ALT mode engages?

 

 

But what about the strange behavior after I had selected a higher speed? Can you tell me why the airplane didn't acellerate to that speed? The engines spooled down immediately after I had selected speed to 210kts and the plane nearly maintained level flight. Should I have pressed the SPD switch before selecting a higher speed?

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Shouldn't the SPD mode engage automatically when the ALT mode engages?

 

It doesn't if you capture the altitude in TOGA mode -- you get THR (REF) | LNAV/HDG/TOGA | TOGA and the speed starts getting very fast, very quickly :).

 

 

 


But what about the strange behavior after I had selected a higher speed? Can you tell me why the airplane didn't acellerate to that speed?

 

Nope, that behaviour looks wrong to me. It should accelerate just fine in FLCH -- though I'd be careful about selecting too high a speed as I seem to recall that FLCH, VNAV etc may allow the aircraft to sink during acceleration (whereas TOGA pitch will not). Pressing SPD, as I say, should have no effect in that regard -- as I say, the only reason for being in the habit of automatically pressing it after FLCH is to take care of the case where you've got a low missed approach altitude, you're perhaps a bit late hitting FLCH and the aircraft captures the altitude before FLCH can engage).

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That's interesting. I will keep that in mind.

Hopefully PMDG will correct this in a future update.

However, thank you very much for your help. :)

 

Regards,

Leif

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Leif,

I've seen the video.

First : FLCH is an FMC driven mode aiming to reach next altitude in 125 seconds or more. It will accordingly set appropriate thrust (not necessarily max as in VNAV SPD). This why you see THR and not THR REF in the FMA window when you climb in FLCH.
In this example at the altitude engaged it is shooting at around 1000 fpm or slightly less at target climb speed in MCP window and current flaps! Not a lot of thrust required for this.

Second: you retract flaps 20 knots below the green marker. You go from 20->10 at the 10- marker and 10->5 at the 5- marker. Not 10->5 at the 10 marker as in the video. Otherwise you have the aircraft hanging out at a very high angle of attack and hit the wrong side of the drag curve. Take also into account that you order the plane to accelerate too and you got very low climb and acceleration rate.

 

PS. FLCH and VNAV SPD do NOT let the aircraft (any Boeing plane in fact) sink in a climb or climb in a descend!

 

Best,

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EMV,

 

I didn't know that FLCH aims to reach the next altitude in a certain time. If so, it seems much more logically to me.

Regarding the flap retraction: Yes, having seen that in the recording I was shocked by what I did myself.

So if I had retracted the flaps on schedule and give the aircraft time to reach the selected speed, the aircraft would have reached the selected 4000ft in >125 seconds with an appropriate thrust setting, right?

 

Thank you for the detailed description. :)

 

Regards,

Leif 

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I believe so.

 

This nice feature is there since the 757 for all Big Boeings ie. the 57/67/47 and 77 chronologically.

 

I believe Boeing introduced this given the vast weight-to-thrust differences these airplanes can have in different flight conditions and as an incentive for the pilot to use FLCH rather than VS. FLCH always protects the plane from going outside the speed envelope while VS does not.

 

Makes sense also for small altitude changes and pax comfort. On a light 744 going from 5000 to 7000 at full thrust it might become a 6000 fpm maneuver. On the other hand, it can be a PITA if you intend to climb only 1000 ft and you have to do it at 500 fpm (use VS instead).

 

Our 777 if you own it has the exact same model.

 

Best,

 

Vangelis

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There are a couple of problems here that I see.

At the acceleration height (1000 feet in this case) you want to select a pitch mode of VNAV or FLCH, which you did. VNAV will increase your speed automatically up to the current flap limit speed minus 5 knots, then you retract flaps on schedule. If you use FLCH, then you need to "Bug Up" to your desired maneuvering speed. Could be 250 knots and you are going to clean up to Flaps Up, or maybe 200 knots and keep the flaps at 5, your choice if you are going to hold. But, procedurally you should increase the speed at 1000 feet more than you did up to whatever maneuvering speed you want to hold.

Second problem, you retracted to Flaps 5 almost 20 knots below the minimum maneuvering speed and you did not bug the speed up. This combination is not a good one on a go-around. You are going to suffer climb wise by doing that and is not safe.

The other problem though seems to be how the model responded to that problem. In FLCH SPD the elevator pitches to maintain your speed and the A/T controls your rate of climb. Clearly, the thrust reduced and should have increased up to G/A thrust. It did not. In fact, it came out of G/A to CLB.

So, in my eyes this is a combination of an improper Go Around procedure, but also the model did not respond as it should have and increase the power up to G/A. Your climb rate would have really been impaired, but you would have kept climbing toward 4000 feet as your speed limped up slowly accelerating.

Edited by Captain_Al

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The other problem though seems to be how the model responded to that problem. In FLCH SPD the elevator pitches to maintain your speed and the A/T controls your rate of climb. Clearly, the thrust reduced and should have increased up to G/A thrust. It did not. In fact, it came out of G/A to CLB.

Erm.. No !

 

On FLCH the thrust limit will switch to either CLB (all engines operating) or CON (engine out).

 

FLCH does not necessarily drive the throttles to max available thrust. See why in post(s) above

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Incidentally, strictly speaking the sequence should be to press FLCH then SPD (the press of the SPD button will not normally have any effect -- it is just in case the aircraft has captured the missed approach altitude whilst still in TOGA which will result in the speed running away) but this should not have any impact on what you are seeing.
0

 

Just for your knowledge, this is not correct. If you push TO/GA to go-around, and you have a low altitude level off and you capture before your acceleration height, at your acceleration height when you push FLCH and bug up to your maneuvering speed or select VNAV, the pitch will change to FLCH SPD or VNAV SPD, the A/T will go to THR or THR REF and when capture occurs again depending on rate, the pitch mode will change to ALT or VNAV ALT, and the A/T will change to SPD automatically. There is no need to push FLCH, then the SPD button. In fact, the SPD button is inhibited anytime you are in VNAV or FLCH on the 400.

 

Now if you capture prior to the acceleration height and you do not select a pitch mode at the acceleration height (improper G/A procedure), that is when you have a problem because you will have THR | LNAV | ALT and no speed control when leveling off, that is when you need to either push the SPD button, or disconnect the A/T and pull the thrust levers back to control speed.

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Just for your knowledge, this is not correct. If you push TO/GA to go-around, and you have a low altitude level off and you capture before your acceleration height, at your acceleration height when you push FLCH and bug up to your maneuvering speed or select VNAV, the pitch will change to FLCH SPD or VNAV SPD, the A/T will go to THR or THR REF and when capture occurs again depending on rate, the pitch mode will change to ALT or VNAV ALT, and the A/T will change to SPD automatically. There is no need to push FLCH, then the SPD button. In fact, the SPD button is inhibited anytime you are in VNAV or FLCH on the 400.

 

Now if you capture prior to the acceleration height and you do not select a pitch mode at the acceleration height (improper G/A procedure), that is when you have a problem because you will have THR | LNAV | ALT and no speed control when leveling off, that is when you need to either push the SPD button, or disconnect the A/T and pull the thrust levers back to control speed.

 

I agree -- that is exactly what I said, and exactly why the Big Airline's B747 missed approach procedure used to be to press FLCH then SPD at Aa. Incidentally, it has now changed and the procedure is to remain in TOGA pitch all the way to misssed approach altitude rather than FLCH SPD at Aa:

At missed approach altitude, select FLCH or VNAV.

If FLCH is selected, press SPD and set speed to the maneuvering speed for the planned flap setting.

If VNAV is selected:

• select speed intervention as needed

• set speed to the maneuvering speed for the planned flap setting

Erm.. No !

 

On FLCH the thrust limit will switch to either CLB (all engines operating) or CON (engine out).

Errm... no ;).

 

Refer FCOM 4.10.7:

Flight Level Change (FLCH) Switch

Push –

• selects FLCH SPD pitch mode

• FLCH SPD pitch mode displays in green (active) on PFD flight mode annunciator

• when IAS/MACH window blank, IAS/MACH window opens to FMC target speed, if valid. If not valid, IAS/MACH window opens to current speed

• when IAS/MACH window open, displays command speed

• when changing from TO/GA to FLCH, IAS/MACH window displays highest value of current airspeed or selected speed

• AFDS pitch holds selected speed. When selected altitude captured, pitch flight mode annunciator changes to ALT

• A/T operates in THR, followed by HOLD mode in descent. When selected altitude captured, A/T mode changes to SPD. A/T advances or retards thrust levers to maintain a vertical speed proportional to the altitude change requested

• with higher altitude set in the ALT window, reference thrust limit changes to CLB when CRZ displayed and to CON with an engine inoperative

Note the critical bit I have highlighted in red ;).

 

I quite agree that FLCH does not necessarily drive the thrust levers to the thrust reference limit, however.

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Erm.. No !

 

On FLCH the thrust limit will switch to either CLB (all engines operating) or CON (engine out).

 

FLCH does not necessarily drive the throttles to max available thrust. See why in post(s) above

 

Hate to disagree with you, but there are 2 situations here on the 400.

 

If you are using FLCH to climb from 4000 feet to 6000 feet, FLCH will attempt to get you there in 2 minutes. So, in this case it would be a climb of approximately 1000 feet per minute for a change of 2000 feet. I agree it will not go to the reference thrust. Not the max available thrust, the reference thrust limit.

 

On a G/A, at the acceleration height, if you use FLCH for the pitch mode, the reference thrust will stay as G/A and not change to CLB until you push the THR pushbutton. So, procedurally at 1000 feet, you would select FLCH, bug the speed to your desired maneuvering speed, retract the flaps on schedule, and then when at your planned maneuvering speed and configuration, select THR, and then check that you have CLB thrust as the reference.

with higher altitude set in the ALT window, reference thrust limit changes to CLB when CRZ displayed and to CON with an engine inoperative

 

Skelsey, this has nothing to do with a Missed Approach...

Or Emvaos, sorry skelsy...

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Skelsey, this has nothing to do with a Missed Approach...

 

Or Emvaos, sorry skelsy...

 

Erm... I'm confused.

 

I think we're having a heated agreement, but just to be clear: the section of FCOM I highlighted is the technical reference that backs up the behaviour that you and I both agree should occur: when FLCH is selected during a GA the reference thrust limit remains at GA.

 

It remains at GA because it only changes to CLB if it was in CRZ.

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Actually, we don't quite agree:

If you push TO/GA to go-around, and you have a low altitude level off and you capture before your acceleration height, at your acceleration height when you push FLCH and bug up to your maneuvering speed or select VNAV, the pitch will change to FLCH SPD or VNAV

 

No - if the aircraft captures the missed approach altitude before you press FLCH then FLCH will not work, however often you press it.

 

Hence FLCH then SPD to protect you from any possible embarrassment. 99% of the time you press FLCH when you are well below the missed approach altitude, all the modes sequence as you describe and the SPD push does nothing.

 

1% of the time you get in to ALT before you press FLCH for whatever reason. However if you press FLCH then SPD this time the FLCH press will do nothing but the SPD press most certainly will. If you are in the habit of always pressing FLCH then SPD then you are always covered and therefore will (should) never cock it up.

 

That's how the World's Favourite have been doing it for many years anyway.

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Simon, I am not heated at all, just call it a friendly debate. I am very calm. I think in your response to me that we agree that on a G/A when you push FLCH, the reference thrust stays in GA, and yes now I see what your point is with that technical reference and what your reasoning is. So, do we agree that in the video, the thrust reference should not have changed to CLB when Mr Leif pushed FLCH. I think we are both on the same page there. In other words, the PMDG model is not correct in that regard.

 

I disagree however with your thought that pushing FLCH will do nothing if you happened to capture the MCP altitude first because of a low altitude missed approach before you get to your acceleration height. So, let's say you go around, you push TO/GA, G/A Thrust, Flaps 20, positive rate, gear up. You are in LNAV or HDG SEL as per ATC and now at 800 feet you capture the 2000 feet in the MCP. At 1000 feet (ACC HT), you push FLCH and bug the speed up to 200, 250, or whatever desired. The jet will go into FLCH (THR, FLCH SPD) and if the climb rate is within capture criteria, will immediately come out and go to ALT, but more importantly, the A/T will go to SPD, which is what you want. You retract flaps on schedule, push THR to get CLB at your flap maneuver configuration and level off at the missed approach altitude.

 

I understand what you are saying about going to FLCH, then pushing SPD, but that is totally unnecessary if you are procedurally correct in doing a missed approach. Where pilots get hosed up is when they do not do a proper missed approach procedure and same scenario, but at 1000 feet, the pilot does not select a pitch mode (he goes brain dead) of VNAV or FLCH and just keeps trucking along. Now, he will will be in THR | LNAV | ALT leveling at the missed approach altitude and there goes the speed off to the races. Now, he needs to push SPD...

 

I can't tell you the number of times I have seen everything I described above since teaching as an instructor, check airmen, and checking on this airplane as an FAA Examiner since 1988. If guys can find a way to hose it up, they will and I more than likely have seen it. If they properly follow procedure, piece of cake. When you say the worlds favorite are doing it this way, who are you talking about? I can't count the number of airlines domestic and worldwide I have taught through the years, but no one ever suggested that as a procedure, and instructors would be debriefing you on it if you did that on a missed approach. That sounds like someones technique, not procedure. Boeing and all the airlines I have ever been associated with would not condone that technique.

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Hi Al,

 

Simon, I am not heated at all, just call it a friendly debate.

 

Absolutely -- sorry, I was being facetious when I referred to our "heated agreement" -- as I say, I think we actually agree on most of this!

 

do we agree that in the video, the thrust reference should not have changed to CLB when Mr Leif pushed FLCH. I think we are both on the same page there. In other words, the PMDG model is not correct in that regard.

 

100%!

 

I disagree however with your thought that pushing FLCH will do nothing if you happened to capture the MCP altitude first because of a low altitude missed approach before you get to your acceleration height. So, let's say you go around, you push TO/GA, G/A Thrust, Flaps 20, positive rate, gear up. You are in LNAV or HDG SEL as per ATC and now at 800 feet you capture the 2000 feet in the MCP. At 1000 feet (ACC HT), you push FLCH and bug the speed up to 200, 250, or whatever desired. The jet will go into FLCH (THR, FLCH SPD) and if the climb rate is within capture criteria, will immediately come out and go to ALT, but more importantly, the A/T will go to SPD, which is what you want. You retract flaps on schedule, push THR to get CLB at your flap maneuver configuration and level off at the missed approach altitude.

 

I am perhaps not being precise enough in my language -- when I say "capture the missed approach altitude" I mean the aircraft goes in to ALT. Imagine a slightly lower GA altitude -- let's say 1400ft for arguments sake, from an airport of elevation ~100ft. You do your go around, you should press FLCH at 1100ft (1000 aal) but for whatever reason you're a bit slow, forget, whatever. The aircraft goes in to ALT as it captures 1400ft.

 

As soon as it goes from TOGA to ALT, FLCH will not work (and if you made it really entertaining by doing a double press of the TOGA switches I imagine you could still be climbing at quite an impressive rate in ALT). This is the trap which drilling people to always press FLCH then SPD seeks to avoid. I understand why it is unnecessary 99% of the time -- but equally I can't see any downsides to the SPD press (can you? I assume Boeing couldn't -- hence the FCOM quotes below), and if it traps the occasional cock-up then it is probably worth it.

 


When you say the worlds favorite are doing it this way, who are you talking about?

 

BA (who as a rule do tend to do some funny things, but this specific one does make a lot of sense to me). As I say, the current procedure actually calls for staying in TOGA all the way to missed approach altitude, with no acceleration at 1000ft aal, although the drill is still to press FLCH then SPD once level at the missed approach altitude. As I quoted from the FCOM earlier:

 

At missed approach altitude, select FLCH or VNAV.

If FLCH is selected, press SPD and set speed to the maneuvering speed for the planned flap setting.
If VNAV is selected:
• select speed intervention as needed
• set speed to the maneuvering speed for the planned flap setting

 

That's the current procedure. I've just done some digging in my hard drive and found a pre-update FCOM (can't put it in a quote box because the forum is complaining!):

 

At acceleration altitude select FLCH then SPD.

Set speed to the maneuvering speed for the planned flap setting.

 

That is in line with how at least one former 747 Training Captain from said airline has explained it to me as well -- FLCH, SPD, 190 (ish) kt. I'm having lunch with a former very senior 744 Training Standards Captain who may very well have actually written the manual in a week or so's time, so I'll have to ask his thoughts on the matter!

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Hi Simon:

 

OK, I totally understand your reasoning as you expressed it. That is a strange procedure, but there are airlines that will incorporate procedures like this usually because somewhere, somehow some scenario happened to them and then they try to pilot proof it. Another reason is they try to standardize the procedure among the different fleets, so transitioning from one jet to another is as standard as possible. I suspect it could be a combination of both with BA.

 

So if I understand correctly, BA will just stay in the go around, once ALT capture occurs, select VNAV or FLCH, push SPD and then accelerate and retract flaps. Doing it this way is kind of close to a 777/787 go around procedure with the exception that most airlines will bug up at 1000 feet, retract flaps, and then once at the planned maneuvering flaps, select FLCH or VNAV and check CLB thrust. No one I know of, with the exception of BA now, pushes the SPD button. But hey if that is their procedure and I am a BA pilot, that is what I do.

 

OK, now I totally see where you are coming from, I have never seen anyone do quite that, but I have seen airlines go out of their way to change procedures usually because one or a combination of the above reasons. See, friendly debate and now we come to a resolution. Good discussion Simon.

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Let's throw a tiny wrench in this...say I'm practicing touch and gos using full manual control, but am following ILS and FD guidance. Obviously, autobrakes are not armed nor are spoilers. What's the procedure after touching down? Is GA or GA+ (two presses) still available after touching down if I had been using manual throttle control? Does the same GA procedure apply if I've already put weight-on-wheels?

 

What if the FD is off during the approach but I'm following the raw ILS signal for guidance? Will the FD reengage upon pressing the TOGA switch to follow the missed approach?

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