B737 WINDSHEAR ESCAPE MANEUVRE [Archive]

Pontius

25th Apr 2012, 05:32

Lucalaz,

As 737OPR said, ignore what he wrote because it was incorrect, of course the autothrottle will move the thrust levers in manual flight.

The machine is intelligent enough to realise the difference between a normal G/A and the windshear manoeuvre, not least because it's gone to great trouble to produce a great big 'WINDSHEAR' on your TV for you. Therefore it is only necessary to push the TOGA switch once. If you do it twice you are not going to fall out of the sky but it will make no difference to the thrust you get. I am guessing that Boeing consider the autothrottle application of max thrust as being aggressive enough to not need to write anything extra about it.

I find it slightly more interesting that in manual flight the autothrottle is disengaged once having applied max thrust, whereas in auto flight it is left engaged. I can understand the reason for disengaging it (stops the thrust changing for some reason when you want it to stay put at max), so why don't we disengage the A/T once max thrust is set in auto flight?

Answer to your question though; push TOGA as many times as you like but you only need to push it once for the windshear manoeuvre case.

de facto

25th Apr 2012, 05:44

The machine is intelligent enough to realise the difference between a normal G/A and the windshear manoeuvre, not least because it's gone to great trouble to produce a great big 'WINDSHEAR' on your TV for you. Therefore it is only necessary to push the TOGA switch once. If you do it twice you are not going to fall out of the sky but it will make no difference to the thrust you get. I am guessing that Boeing consider the autothrottle application of max thrust as being aggressive enough to not need to write anything extra about it.

Seriously?
This is a tech log forum,not a forum to get some guesstimate advise from a PC sim player.
No grudge against you but come on,bit obvious here.no?

, so why don't we disengage the A/T once max thrust is set in auto flight?

Why would you if the automatics are doing their job properly?

Pontius

25th Apr 2012, 05:57

I'll bow to your superior knowledge De Facto. I don't actually own a flight sim program and only have around 15000 hours from mil fast jets to the B744, so I'm still learning. Now, admittedly, I didn't converse in tech speak but please enlighten me as to the errors in what I have written.

Why would you if the automatics are doing their job properly?

As you like to answer questions with questions: If this is the case and the automatics are doing their job properly, why disengage the A/T in manual flight once max thrust is set. Here's a clue; I've already given you the answer in my to Lucalaz. I'm not interested in why we leave it engaged, I'm interested in why why don't disengage it, as you would in manual flight.

737OPR

25th Apr 2012, 05:57

Pontius,

OP mentioned the case A/P and A/T off, pretty sure that in that case, pushing the TOGA buttons will not advance the thrustlevers( unlike the 747)!!!

My edit was because I stated that for both manual and autoflight Boeing says to manually advance the thrustlevers. Reviewing my old manual I found that statement to be incorrect. In autoflight Boeing does not mention to advance the TL manually. So I deleted that sentence. You may say ignore my post.....be my guest.. By all means

de facto

25th Apr 2012, 06:28

The machine is intelligent enough to realise the difference between a normal G/A and the windshear manoeuvre,
Really?and how does the 'machine' responds differently in each case?

it's gone to great trouble to produce a great big 'WINDSHEAR' on your TV for you
Please explain..
Therefore it is only necessary to push the TOGA switch once
Once to get initial pitch guidance,but twice to get max limit thrust.
If you do it twice you are not going to fall out of the sky but it will make no difference to the thrust you get.
Wrong.One click you get 2000ft/mim ,second whatever max thrust gives you for your pitch IRRESPECTIVE of your 'machine' being in a windshear or not.
why disengage the A/T in manual flight once max thrust is set.
Not a boeing procedure.
I'm interested in why why don't disengage it, as you would in manual flight.
Not a boeing procedure.

Cant be different than on your 744 'machine' no?

Pontius

25th Apr 2012, 06:37

737OPR,

Sorry mate, didn't mean to sound so rude and I certainly won't ignore you. My written word does not convey the light-hearted manner in which I was trying to write. I won't change my post or else it'll make the whole thread nonsense but I was trying to be jocular and not the prat that I can see my reply made me out to be :sad: Edited bit: I now see what you meant about A/P & A/T off....see explanation below....boy I'm cocking this thread up :confused:

You're right about the subtle differences between aircraft and I'm yet to add 777 to my flight sim add-ons of 73/74/75/76, so cannot comment about that beast, but I think for the others Boeing decided to save some money and didn't bother changing the windshear logic between aircraft. Okay, it's probably a lot more technical than that but they all seem to work the same way.

PS: When I say 737 I'm talking 3/4/500. I've never played with the NG, so have no idea what MS have programmed into that.

Edited in a HUGE way because I forgot the 737 disengages the Arm switch when you disengage the A/T. Therefore reference to 'smart' modes etc was complete bollox.

737OPR

25th Apr 2012, 06:48

Pontius,

Ok, no harm done! You are right in the differences between AT armed and OFF.

For your question about disengaging after selecting full thrust in manual v. Leaving it on when in autoflight....I can only guess that Boeing has done a risk assessment and found that auto flight deals with the situation adequately. Whereas in manual flight you may be faced with a high pitch angle, the AT sensing altitude capture and starting to reduce and the pilot not reacting quickly enough. Liability and all.( that's just a guess on my part do and may be wrong)

Greetings

Pftt, de facto, I guess I'm starting to get confused between types as well now!!
If in fact the AT was off and you manually advanced it it will not reduce at alt capture, you are right! In the 74 with the AT off it will actually re engade the AT with the first push of TOGA and Boeing states to disengage the AT after full thrust is set.

I'll bow out now, but stand by my first answer to the OP that one push only is necessary in autoflight,because the AT will go to whatever thrust setting that is necessary to achieve the 2000fpm, whether it be full or or less.

Denti

25th Apr 2012, 07:04

why disengage the A/T in manual flight once max thrust is set.
Not a boeing procedure.

Care to elaborate? According to the 737QRH Non-Normal Maneuvers it is actually a boeing procedure.

Anyway, even in automatic flight the automatic flight system might not be able to cope with a windshear, one must be prepared to switch it all off and fly it manually in any case.

de facto

25th Apr 2012, 07:16

Quote:
, so why don't we disengage the A/T once max thrust is set in auto flight?

That was the quote i was responding to.
In autoflight,the AT is NOT to be disengaged after thrust is set automatically.
The reason is that the AT get info from many sources to produce the max thrust(via ADIRUS/EEC) and disconnecting it would not achieve the initial goal to get the max optimum thrust.
The at will protect from flap overspeed and vmo while and when you decide to retract the flaps when windshear is clear...
As denti pointed out ,manual override may be needed is the automatics arent doing what they are supposed to do,for that the pilot must first get to grips with knowledge of its automatics,no?

Pontius

25th Apr 2012, 07:37

De Facto,

I know it's not Boeing procedure but this is the tech forum and I wouldn't mind knowing why the difference, as opposed to just the pat answer of 'because it's not Boeing procedure'. I won't do anything other than that written in the QRH and I'm not suggesting we should. I would just like to know why one procedure has you disconnecting the A/T, whereas the other doesn't. In both cases the A/T system is working properly and in both cases you have the same pitch guidance on the FDs. I'm not going to lose sleep over not getting an answer but it came about because it's slightly relevant to this thread.

I suggest the argument for disengaging the A/T is because you don't want it doing strange things to you at an inopportune moment. You tell me I shouldn't be concerned if the automatics are working properly and that we don't disconnect the A/T in auto flight but do in manual flight because it's procedure. Hardly an answer to ponder as I hit F2 to get my gear down.

Finally you tell me I'm worried about G/A mode reducing thrust on me, suggesting I don't have a clue what I'm talking about. Fair enough with your assessment of my knowledge but let's take a possible scenario: you're happily established on an ILS at 1000' with all the automatics in and a missed approach altitude of, say, 4000' in the MCP. Up pops Windshear, so you do your stuff. I say you press the TOGA buttons once because the windshear logic will give you max N1, you say twice. I won't argue at this point because we've got a windshear warning, so go ahead and press it as many times as you like and back into the sky we go. We're climbing at a hefty rate; max N1 and 15 degs nose up and what happens next? Even though we're only at 3000' we're climbing quickly and Alt Cap. The speed window is open at your present speed. Ahhh, says Mr A/T I'll drag back the thrust to keep the speed, even though we've still got 1000' until that MCP alt. Now, I would suggest I don't want the A/T reducing power on me during a windshear escape manoeuvre but you're saying it's Boeing procedure that we don't disengage the A/T in auto flight. I know it is but why, especially as this wouldn't happen in manual flight?

Am I worried? No. Despite your suggestion that my system knowledge is sadly lacking, can I conceive a realistic scenario where the QRH actions could mean more, unnecessary, work for me on the day? I think I can.

Sadly, the modern Boeing 'tech' manuals are sorely lacking detail and rather economical in the way they are written. I've looked in the books for my Boeing types and none of them make specific reference to the way in which the A/T functions in a windshear G/A situation. I accept 100% the way in which it works normally, with 1 or 2 presses of the buttons but it is only through empirical evidence that I can write about the differences in G/A logic.

I've just got off the phone to a trainer mate of mine. Now, it could be that we're both wrong and, without getting in the sim, we're not going to be guaranteed the absolute, no s%4*t, 100% truth but he has suggested the same as me i.e. that the windshear warning being generated changes the logic of the G/A and 1 press will give max N1. The QRH doesn't help because it only talks about ensuring 'GA power' is set, rather than max GA but this is the same script for all the Boeings in my logbook, so rather unspecific.

Anyone going to the sim soon?

Pontius

25th Apr 2012, 07:43

The at will protect from flap overspeed and vmo while and when you decide to retract the flaps when windshear is clear.

Whether you're flying manually or have the A/P engaged. So why leave it engaged with A/P but not when manually flying?

The reason is that the AT get info from many sources to produce the max thrust(via ADIRUS/EEC) and disconnecting it would not achieve the initial goal to get the max optimum thrust.

Max N1 is max N1, whether it's the A/T moving the thrust levers or the pilot. The EECs are the things that give you max thrust and will prevent you over-boosting (thrusting) the engines, not the A/T, so your statement does not make sense.

Bet you wish you'd never accused me of being a flight simmer :)

de facto

25th Apr 2012, 08:04

Max N1 is max N1, whether it's the A/T moving the thrust levers or the pilot. The EECs are the things that give you max thrust and will prevent you over-boosting (thrusting) the engines, not the A/T, so your statement does not make sense.
Jeez,we are talking as you go around,thrust in auto mode,thrust is at max,then you say why not disconnect...
Im telling you unless you wanna keep on changing the thrust (manually)to achieve a continuous max thrust,then let the AT engaged.:ugh:
The AT COMPUTER is using eec and adirus info to advance the thrust LEVERS to their optimum max thrust.
And by the way overboosting max N1 as you say is possible with the EEC,with the AT OFF.
The EEC has only an extra protection to avoid n2 overSPEED,not N1,via an overspeed governor.
In that case eec will command the fmv to reduce fuel to engine hence reducing n2.

grounded27

25th Apr 2012, 08:14

You guys scare me, is not TOGA thrust, wings level and 10 deg nose up standard for all aircraft? Damb simple as I may ignorantly understand.

Shiny side down

25th Apr 2012, 08:15

Whether you're flying manually or have the A/P engaged. So why leave it engaged with A/P but not when manually flying?

I wondered at this too, sometime back, and wondered if it was somehow tied into the whole automatics usage. Either all, or none.

When I was first flying 737(NG and Classic) nearly a decade ago (ouch), there were many proponents advocating leaving auto throttle engaged at all times, and active, even during the flare. Others who would use speed off (armed, for etc)

Later, it was manual control- then manual thrust. Autopilot on, then auto thrust ( unless it's not working, which happened several times).
There's numerous contradictions scattered through this concept, and I for one have never fully subscribed to the philosophy, although I will abide by the SOP.

de facto

25th Apr 2012, 08:17

grounded27 You guys scare me, is not TOGA thrust, wings level and 10 deg nose up standard for all aircraft? Damb simple as I may ignorantly understand.

Yes,ignorant.

Pontius,
In the case of an AP engaged and AT engaged,if you see alt acq,and you are still in the windshear, by all means disconnect the automatics.

captplaystation

25th Apr 2012, 08:18

Despite what Boeing says, anyone leaving the automatics engaged during a Windshear escape manouvere is perhaps being a little bit too trusting IMHO.

AT all sorts of possibiities, and from what I have seen of the AP in something less than severe turbulence , on several occasions, you could get handed CWS at any moment anyhow, so why not fly it ?

Shiny side down

25th Apr 2012, 08:28

on several occasions, you could get handed CWS at any moment anyhow, so why not fly it ?

No issue with that at all (unless you see me in wobble-mode), but it doesn't address the technical reasonng.

Pontious (i believe) made a comment earlier about the Boeing manuals being increasingly vague and bereft of Indepth knowledge(my words), which does leave a number of unanswered questions that simply have a 'procedure' with no technical understanding of the why.

By all means follow the procedure as laid out. But it would still be good to know how we got to that point.

de facto

25th Apr 2012, 08:32

Despite what Boeing says, anyone leaving the automatics engaged during a Windshear escape manouvere is perhaps being a little bit too trusting IMHO.
True.
On the other hand pilots may believe their skills on that day may bring a better outcome.Maybe,maybe not.
Never experienced a strong downdraft shear in real life.
What i can say is during low altitude phase,(take off/landing)with AT engaged already,disengaging it is not making use of your resources properly.
If GA thrust is not enough at that time and the ground is coming back at you then yes firewall the damn thing.

737OPR

25th Apr 2012, 08:47

Pontius,

Send you a pm.

RAT 5

25th Apr 2012, 09:08

Regarding A/T on/off: I digress slightly as this comment is not specifically about W.S. escape. And firstly I have to disagree with Boeing's 1 size fits all philosophy.
On the B737 classic the TCAS RA manoeuvre was disengage A/P and follow the red prism guidance. You left A/T engaged, which I thought a splendid idea. In the stress of the moment speed control was one less thing to relax about; the escape and the recovery afterwards.
On the NG Boeing disconnects A/T. When I asked Boeing pilot he said it was to comply with Boeing's philosophy of manual flight = manual thrust. How pedantic is that? I suggested they had introduced a massive threat, and perhaps after the first RA followed by stick shaker they would be reviewing their procedure. There was little reaction, but a note was made. On your day, when you are at the sharp end wrestling with the bronco you may choose to use the depth of airmanship you have and do what is necessary rather than dither around.

B737900er

25th Apr 2012, 09:20

Like Rat5 said Boeings philosophy is manual flight = no A/P no A/T.

Regarding the W.E.P in manual flight; if you are flying single channel and hit TOGA the A/P kicks out reverting you to manual flight with A/T engaged this would be contradicting their philosophy about manual flight.

Automatic flight or Dual Channel: by pressing TOGA will allow a full automated GA, but like a previous poster said ' be prepared to go manual flight and don't rely solely on the automatics'.

Checkboard

25th Apr 2012, 09:34

On the NG Boeing disconnects A/T. When I asked Boeing pilot he said it was to comply with Boeing's philosophy of manual flight = manual thrust. How pedantic is that? I suggested they had introduced a massive threat, and perhaps after the first RA followed by stick shaker they would be reviewing their procedure. There was little reaction, but a note was made. On your day, when you are at the sharp end wrestling with the bronco you may choose to use the depth of airmanship you have and do what is necessary rather than dither around.

Say you're in a LVLCHG descent, autothrottle commanding idle thrust, Flight Directors showing, say 8º down pitch for the descent - and a "TCAS Climb" event occurs. You disengage the autopilot and pitch up, away from the Flight Director command, and follow your pre-decided non SOP action of leaving the autothrottle engaged.

What does the autothrottle do? Does it remain in idle thrust, attempting to follow the valid Flight Director commands for the idle descent? Are you only hoping for the Alpha floor function to save your stall as you pitch up without adding power?

de facto

25th Apr 2012, 09:58

Flight Directors showing, say 8º down pitch for the descent
Quite a steep descent there.. 2 deg from an upset recovery..
and a "TCAS Climb" event occurs. You disengage the autopilot and pitch up, away from the Flight Director command, and follow your pre-decided non SOP action of leaving the autothrottle engaged.
B737NG:RA= AP+AT OFF.

Are you only hoping for the Alpha floor function to save your stall as you pitch up without adding power?

This 'alpha floor' doesnt work if your aircraft altitude is above your MCP altitude.

Cornish Jack

25th Apr 2012, 10:38

Could I suggest that an exceptionally good training video on windshear, produced by an AA training captain, should be required viewing for ALL. We used it at Virgin for recurrent training and the specifics of what was recommended were succinctly laid out, with reasoning and inarguable! "Stow the boards, Thrust to maximum, auto throttle OFF, wings level, pull to stick shake, if necessary". The accompanying video of the example W/S event at Dallas(?) L1011 should reinforce the necessity for fast, instinctive reaction.

de facto

25th Apr 2012, 10:57

Stow the boards
You are flying Airbus?:E

Once Max thrust is set with AT OFF, does your SOP require both hands on the wheel or not?
I would think pitch control near the PLI would be smoother with both hands ON.
What you think?

Ditched

25th Apr 2012, 11:08

..From my QRH (737NG)

Push TOGA, this puts the AFDS in G/A mode,
Disconnect AT and AP! (AP drops off anyway if youre single channel)
MAX Thrust, (manually)
Aggressively pitch up to 15 deg or stick shaker wichever comes first. Disregard the Flight Director.
Pray you've got enough air under the wings
Wait untill youre out of the WS
Then clean up and have a chat with ATC

I would never leave automatics in, you'll need both hands on the control column with the stong pitch up moment cauesed by the engines. No time to start messing around with the autothrottle if its not doing what you want.... anything other than full thrust.

hope it clears some things up. seems to be quite a bit of confusion around here.

be safe!

Pontius

25th Apr 2012, 11:09

In the case of an AP engaged and AT engaged,if you see alt acq,and you are still in the windshear, by all means disconnect the automatics.

Thank you for stating the obvious, De Facto, but you've conveniently avoided the technical aspects of the scenario I postulated. I imagined such a situation to counter your suggestion that my G/A knowledge was lacking and that my technical savvy not up-to-scratch. Now, that's a fair call but if you're going to do that, then at least have the decency to tell me how the A/T remaining engaged in auto flight will solve the problems of, effectively, a low level altitude capture situation which could really cheese you off in a windshear situation, which wouldn't happen with the A/T disengaged. Just as a reminder; I am not advocating disconnecting the A/T. I am saying I will stick to the QRH but I would like to know why the difference :confused:

You guys scare me, is not TOGA thrust, wings level and 10 deg nose up standard for all aircraft?

No, Grounded, that is not standard for all aircraft. Luckily for you we do know what is required of our aircraft, so you can rest assured and feel less scared :rolleyes:

When I asked Boeing pilot he said it was to comply with Boeing's philosophy of manual flight = manual thrust.

This may very well be the answer and that's an end to it. I know the guys with big brains in Seattle/Toulouse figure this stuff out and I'll do what they say but I sometimes like to know why and this is one of those times. As I said to 737OPR in my PM, 99.9% of this is theoretical and the scenarios are quite contrived. You're pretty well going to end up going manual anyway (my 3 events did), so the point is almost moot. However, as this is the tech forum I'm going to suggest that disengaging the A/T will stop the power coming back when (theoretically) you don't want it to and this is good in manual flight, so why not click them out once thrust is set by the A/T in auto flight? If manual flight = manual thrust and auto flight = auto thrust is the answer to my question, have the big brains thought about the unwanted thrust reduction suggested in my (pretty farfetched) scenario or have I failed, again, in my ability to see the Big Picture and risk assess :)

"Stow the boards, Thrust to maximum, auto throttle OFF, wings level, pull to stick shake, if necessary"

But not if the auto pilot is engaged :E I know I'm being trite....but that's what's written in my QRH ;)

Denti

25th Apr 2012, 11:28

@Ditched, that seems to be a company specific maneuver, it is not the standard boeing one which has two different ones for using automatics or not.

wiggy

25th Apr 2012, 11:29

grounded27

You guys scare me, is not TOGA thrust, wings level and 10 deg nose up standard for all aircraft?

No.

Next question.

Centaurus

25th Apr 2012, 12:48

I suggested they had introduced a massive threat,

Not if you are competent at hand flying the aircraft in all respects. On the other hand if you are one of the automatics addiction mob (and I am sure you are not of course:E), then any change from automatics to manual will have the potential to introduce a massive threat:ok:

Centaurus

25th Apr 2012, 12:50

say 8º down pitch for the descent

With THAT sort of pitch attitude you are courting serious trouble within a few seconds...

sheppey

25th Apr 2012, 13:20

"Stow the boards, Thrust to maximum,I note the AA pilot advice was to first "stow the boards" by which one presumes he means retract the speed brakes first.

In contrast, that personal advice perhaps for his own aircraft type, is at odds with the windshear advice published in the the Boeing 737 QRH . There, it states the speed brakes are retracted after the autopilot is disconnected, max thrust is applied and after rolling the wings level, and rotating towards an initial pitch attitude of 15 degrees. Of course all this happens very quickly.

The GPWS pull up manoeuvre is slightly different in that the initial pitch attitude is 20 degrees but the speed brakes are still retracted in the same order of events as the windshear escape manoeuvre.

The 20 degrees attitude was introduced after the Air New Zealand Mount Erebus crash when the DC10 hit Mt Erebus following a GPWS warning. At the time the GPWS pull up policy set by the major manufacturers was to select go around attitude of 15 degrees. Later research into CFIT accidents revealed that statistically 20 degrees gave you a better chance of getting away with it.

ImbracableCrunk

25th Apr 2012, 14:16

This 'alpha floor' doesnt work if your aircraft altitude is above your MCP altitude. Are you saying that because he's now attempting a climb? Min Speed Reversion definitely works when you're above your MCP alt, but the A/P kicks out if you can't - in a climb - maintain a min airspeed and climb rate.

737OPR

25th Apr 2012, 19:19

Does everybody realize how far the thread has drifted from the OP's original question? :)

Cornish Jack

25th Apr 2012, 20:43

latetonite

25th Apr 2012, 23:29

The TOGA gives you a 15 degrees FD command, for guidance. Trust is manually firewalled.........come on guys..

de facto

26th Apr 2012, 05:12

Are you saying that because he's now attempting a climb? Min Speed Reversion definitely works when you're above your MCP alt, but the A/P kicks out if you can't - in a climb - maintain a min airspeed and climb rate.

I am saying that as he mentionned pitching up without adding thrust.

The 737 auto-throttle system will increase thrust to maintain its minimum speed (the books say approx 1.3 v/s) however what the book does not say is that if the MCP altitude is above current altitude that is true.However if the aircraft is below the current altitude then the thrust will close and the elevator will pitch down to minimum speed. Min Speed reversion is an MCP SPD mode.

Pitch 15 then firewall? How about max thrust initially?

c100driver

26th Apr 2012, 05:36

The 737 auto-throttle system will increase thrust to maintain its minimum speed (the books say approx 1.3 v/s) however what the book does not say is that if the MCP altitude is above current altitude that is true.However if the aircraft is below the current altitude then the thrust will close and the elevator will pitch down to minimum speed. Min Speed reversion is an MCP SPD mode.

Finally someone else get it!

de facto

26th Apr 2012, 09:05

De Facto, but you've conveniently avoided the technical aspects of the scenario I postulated. I imagined such a situation to counter your suggestion that my G/A knowledge was lacking and that my technical savvy not up-to-scratch. Now, that's a fair call but if you're going to do that, then at least have the decency to tell me how the A/T remaining engaged in auto flight will solve the problems of, effectively, a low level altitude capture situation which could really cheese you off in a windshear situation, which wouldn't happen with the A/T disengaged. Just as a reminder; I am not advocating disconnecting the A/T. I am saying I will stick to the QRH but I would like to know why the difference

Ok, I'll try to explain my thought one last time on this issue.
The reason why I initially disagreed with your earlier post (suggesting to disconnect the A/T after GA thrust was established in a A/P GA maneuver),was because in A/P GA (in 737,both channels would have to be engaged before the GA initiation),the AT should remain engaged as per Boeing procedure.(automatic Windshear GA procedure).
Now,we all know that a windshear GA (and by windshear I mean convective windshear,downdraft... ), there is very little chance the aircraft would be set up for a cat 2 app.(both AP engaged) for many reasons.Therefore the AP will be on single channel.
Pressing the TOGA buttons will give you the FD INITiAL pitch guidance and AT reduced GA thrust(click once),when the first thrust is set,(a second click will provide full n1 limit GA thrust).
THEREFORE,if you disconnect the AT when the first GA thrust is set you will NOT have full thrust.
Disconnecting the AT (to follow boeing procedure as you are now in a MANUAL GA) should be done when max thrust set.

I FULLY AGREE with you that the FDs,during a GA will give you alt aqc/hold pitch guidance when you approach /level off your MCP altitude,the AT will engage in Speed mode and will reduce the thrust.
Now I am sure,as a 15000 hrs experienced pilot knows the difference between a windshear due to a downdraft(low climb rate) or just a sudden rapid change of wind speed/direction(gust/inversion).
In a downdraft,the missed app altitude goes out of the window,last of your problem,so disconnecting the AT after full thrust is a good idea to do ,and that would be following boeing.
When you get windshear warning (wx radar senses a horizontal draft,automatically assumes the vertical is the same and calls windshear ),i believe a ga windshear is to be performed,however you will probably be out of this 'windshear' zone very quickly,in that case maintaining the AT engaged will,when you alt acq your missed app altitude(by then the windshear alert will be gone) will allow you to accelerate with all the protections the AT is to give.
Hope im bit more clear:)

latetonite

26th Apr 2012, 09:17

I do not understand the need for elaboration on automatics. Boeing says you disconnect A/P and A/T. That leaves you with manual flying. As you press TOGA, you get most of the time a 15 degrees pitch up command. Then firewall the thrust levers. Your EEC`s will take care of max thrust.If not worry about this later. If needed, increase pitch up to stick shaker to have a positive climb rate, and stay away from the ground.
Did I miss something in the question?

de facto

26th Apr 2012, 09:24

Then firewall the thrust levers. Your EEC`s will take care of max thrust
EEc dont provide overthrust protection with the AT OFF,firewalling will damage your engine.
Firewalling should be done in the last resort,as you say to stay away from the ground rather increasing your climb rate.
Dont you agree?

Lord Spandex Masher

26th Apr 2012, 09:42

Quite a steep descent there.. 2 deg from an upset recovery.

No, not really.

no sponsor

26th Apr 2012, 09:44

Disconnect the thrust in the manual W/S case, once G/A pwr is set to avoid capturing an altitude, and the aircraft reducing thrust.

If you don't get the windshear warning, but suspect w/s, you must fly the aircraft in the manual mode, since it will assume you are just performing a normal G/A, and will not command the F/D to 15 degrees nose up.

Pontius

26th Apr 2012, 09:51

I do not understand the need for elaboration on automatics. Boeing says you disconnect A/P and A/T. That leaves you with manual flying.

Latetonite,

Maybe it's just your specific Company manuals that say manual flight only but the Boeing manuals, used by a good deal of companies, offer the option of an 'automatic' windshear G/A i.e. one in which the A/P & A/T remain engaged. Of course you must obey your Company's procedures in that case. As I've said before, we're postulating scenarios which are pretty unrealistic i.e. we know that it is very unlikely that we're going to remain in auto but it's fun to explore these things in the comfort of a room, rather than trying to think about them when it goes for a can of worms on the day.

De Facto,

Don't get me wrong here, I'm not being a deliberate ass but rather acting as a really argumentative Devil's Advocate and I'm only doing that because, apart from manual flight = manual thrust and auto flight = auto thrust (which is quite probably THE answer), nobody has come up with a decent reason why we shouldn't disengage the A/T once max G/A is set. I'm quite happy if that is the answer but I still think there will be a better one that the clever people can come up with.

Anyway, you wrote:

In a downdraft,the missed app altitude goes out of the window,last of your problem,so disconnecting the AT after full thrust is a good idea to do ,and that would be following boeing.

I agree that missed approach alts etc go out of the window and remember I'm being a theoretical bore here. But returning to the scenario I suggested and which you've answered including the quote above, you've still got the automatics in, therefore it wouldn't be following Boeing to disconnect the A/T. You become distracted by something (very easy to do with the nasty windshear situation you're experiencing) and alt acquire will bring back the thrust, which we agree is bad, hence my thinking that A/T disconnect WITH A/P engaged may have SOME merit, in theory alone.

I do realise that we are talking about the 737 and I do agree that both A/Ps engaged adds an even more far-fetched aspect to the scenario but if I can just expand it a little and add that this windshear manoeuvre is common to the 74/75 & 76 (don't know about 77), which will do this single channel and yet have the same thing written about leaving A/T engaged with A/P and off with manual flight. That probably adds even more credence to the answer being the Boeing manual/auto flight philosophy but this is where the eggheads hang out and they might know an even better reason.

de facto

26th Apr 2012, 09:54

Quote:
Originally Posted by de facto
Quite a steep descent there.. 2 deg from an upset recovery.
No, not really.

Well on the B 737, yes really.more than 25 deg up and 10deg nose down is qualified as a flight upset.

But returning to the scenario I suggested and which you've answered including the quote above, you've still got the automatics in, therefore it wouldn't be following Boeing to disconnect the A/T
True,however,since you dont want to level off at your selected ALT,you would have to disconnect the APP,which leads you to manual flight therefore AT OFF.
You can also chose to select a higher mcp alt....and stay in AP mode with AT engaged....

Lord Spandex Masher

26th Apr 2012, 10:33

Well on the B 737, yes really.more than 25 deg up and 10deg nose down is qualified as a flight upset

Unintentionally yes, but I would suggest that following FD demands, as in Checkboards post, it wouldn't be unintentional.

Pontius

26th Apr 2012, 11:19

True,however,since you dont want to level off at your selected ALT,you would have to disconnect the APP,which leads you to manual flight therefore AT OFF.
You can also chose to select a higher mcp alt....and stay in AP mode with AT engaged....

Now you're being specious and avoiding the point entirely.

Our imaginary pilots are in windshear, they're getting battered around and are concentrating on the performance instruments. They are monitoring the rad alt versus terrain closure and they're keeping an eye on the speed etc. They've decided it's a good idea to leave the A/P & A/T engaged but, with all the other distractions around the place, including ATC etc, they've not seen the FMA change. The rate of climb means the A/T will drag the power back. They don't want to level off but they don't realise they're going to since they haven't noticed the FMA change, therefore they're not going to do the correct thing i.e. manual flight. Likewise, because they haven't noticed the FMA change they don't realise they need to increase the MCP altitude.

I said in the beginning it was an unlikely, but possible, scenario and I stick to that. It is not beyond the whit of man to fail to see that little green box appear on the EADI and appreciate all that it means, especially with all the other things going on. By simply saying they could go to manual flight or increase the MCP altitude, which I know are solutions, you are avoiding answering the question about the reason for leaving the A/T engaged in auto flight. 'Because Boeing say so' is true but it is not an answer worthy of such an august forum :) So, come on, why (besides the Boeing procedure) can we not disengage the A/T, in auto flight, once G/A thrust is set, thereby avoiding the possibility of power reducing in the event of altitude acquire?

A37575

26th Apr 2012, 13:21

Apologies, don't want to continue off topic, but the"Stow the boards" etc. was this instructor's suggested sequence to ensure that there would never be a repeat of past errors - viz. attempted go-around with the speed brakes deployed and/or auto throttles retarding (Uncommanded by crew) It happened, and with Murphy ever present, book or no book, I know which sequence I would prefer!

And isn't this a typical example of an instructor convincing his students that his theories are best and by inference to disregard the manufacturer's recommendations. Has this instructor conducted measured and verifiable tests of his theory? No wonder one hears the oft repeated complaint by students that lack of standardisation between instructors is most annoying.

de facto

26th Apr 2012, 13:52

So, come on, why (besides the Boeing procedure) can we not disengage the A/T, in auto flight, once G/A thrust is set, thereby avoiding the possibility of power reducing in the event of altitude acquire?

Of course you can disengage!Boeing cant make procedure for every possible scenario..can they?
Now they dont say that the AT MUST be ON,it is RECOMMENDED procedure.
For the rest you are paid to use sound judgement in different possible scenario with your knowledge/experience/skills/aircraft manufacturer standard procedure/SOP/Airmanship....blablabla.
There is NO TECHNICAL reason,some aircraft were not even fitted with AT...i believe it was the case when SWA got their 737s.

Lord Spandex Masher

26th Apr 2012, 13:53

Why when someone posts a tech question can people not go and get the correct answer before posting? We have 3 pages of debate here!

Why bother posting a question if you can "go and get the correct answer"?

:rolleyes:

Cornish Jack

26th Apr 2012, 13:54

A37575 - could be! However it could also be that this particular instructor has a well-developed instinct for survival and KNOWS that, whatever else is going on, following that sequence gives him the best chance of still being around to pass on his unverified ideas!:rolleyes:

See Rumour and News thread "This is not about stick and rudder skills" reply No 8 by Tubby Linton.

de facto

26th Apr 2012, 14:15

Here is the original question:

As we know by pressing the TOGAs once it will only give us a reduced goaround thrust so I assume Boeing wants us to push them twice, is that correct?

Boeing does not mention pressing it twice during the automatic procedure,just to press the toga switch,get the pitch and check GA thrust is annunciated on the FMA(yes people still must read the FMA during auto windshear GA)
Durimg the manual,boeing states to aggressively apply MAX thrust.

So yes i believe Boeing expect the crews to know 2 clicks needed to get MAX thrust,one click to get reduced,when thrust stabilised another click to get N1 limit thrust (what I believe they call MAX and NOT FiREWALL which may over thrust the engine,at least momentarely while the EEC tries to cope with the thrust lever yanking).

There.I am done here.:ouch:

ImbracableCrunk

26th Apr 2012, 16:39

EEC does provide full overboost protection if in normal mode. PMC will not.

lucalaz

26th Apr 2012, 18:49

DE FACTO thanks for quoting my original question. That's exactly what I wanted to know and it would be interesting to know if someone else could confirm what you've just said.

I do also apoligise as my question was specifically refering to the 737NG.

If in doubt during the AUTOMATIC FLIGHT case I'd push the TOGAs twice, three or even four times. As long as A/T is giving me full power to escape the WS I am happy, otherwise I'd disconnect everything and revert to the MANUAL FLIGHT case as per QRH. Mine was purely a question aimed to improve my knowledge of the automatic systems. :8

Thank you guys for all your answers provided so far and if anyone has anything else to add, please do. :ok:

captplaystation

26th Apr 2012, 19:22

Ref my Prev post (#19) I suggest watching the video "Children of the Magenta Line" , link on post# 8 on the thread in R&N "This is not about better Stick & Rudder skills"

I think somewhere in there, others, with much more experience than me, will support my assertions.

latetonite

27th Apr 2012, 01:21

Capt Playstation, you got it, immediate lower the level of automatics to almost none, i.e. manual flying. In a windshear there is no time selecting, verifying, checking and typing and get caught out.
De Facto, please check vol 2. I am talking about the 737NG. Are you typed on this airplane or are you referring to the classic 737?
And a windshear escape in automatics appeared in none of the manuals of the companies I`ve flown for. But my experience is limited of course and I am always eager to learn.
If we do have to consider all the post replies here during a windshear event, the probability for survival looks remote.

de facto

27th Apr 2012, 02:50

De Facto, please check vol 2. I am talking about the 737NG. Are you typed on this airplane or are you referring to the classic 737?
I am talking about the NG.
I know what your manual says,EEC protection in Normal mode.

Now i may be wrong,but i believe that WITHOUT AT even in Normal mode,a thrust overshoot is possible if thrust levels are firewalled.
I call a thrust overshoot,a thrust higher than the GA thrust calculated by the FMC.(GA N1 limit).
FULL FWD lever position thrust is limited by the EEC for the highest rating the engine can take,ie B737-8(ur fmc shows 26k) ,the engine at full forward stop will give you 27k.
I call this an over thrust for the actual conditions.
If someone can explain me otherwise,i would be quite happy to listen and maybe learn:)

If in doubt during the AUTOMATIC FLIGHT case I'd push the TOGA twice, three or even four times. As long as A/T is giving me full power to escape the WS I am happy

No need to get crazy on these switches either:E
Ok,if you press TOGA once,you will get the FD into GA mode and reduced GA thrust.( your FMA will read GA/TOGA/CMD) GA is reduced GA thrust,TOGA is for your pitch,and CMD is cause your AP is engaged.
When the thrust is stable, click one more time:and you will get full GA thrust(FMC N1Limit) and your FMA will read N1/TOGA/CMD.
In brief, when you see N1/TOGA, stop clicking:E

Denti

27th Apr 2012, 08:00

@latetonite boeings windshear escape maneuver at least for the NG if not for the classic has two parts, the first one is manual flight, the second one is automatic flight. There is a note advising that severe windshear might be beyond the capability of the auto flight system and in that case the pilot is to disconnect both auto thrust and autopilot and fly it manually. For most windshear encounters however automatic recovery actually works fine according to simulator checks agains historical windshear data. Never had a reactive windshear warning in the NG, only predictive windshear warnings which usually resulted in being clear of the actual windshear.

However as others have said that only applies if an automatic go-around is possible. Since we fly all precision approaches dual channel that is the case in "my" outfit as long as the autopilot isn't disconnected and of course the same if above 400ft after take off if one was lazy enough to engage the autopilot that early.

@defacto it is my understanding that "maximum thrust" as mentioned in the escape maneuver is indeed the maximum certified thrust for the engine, which could be above the max rating for the airplane in question. However it is still within limits for the engine therefore it will not damage the engine, but may increase maintenance cost in the long run if one does it every week or so.

de facto

27th Apr 2012, 08:13

However it is still within limits for the engine therefore it will not damage the engine, but may increase maintenance cost in the long run if one does it every week or so
I agree.
For most windshear encounters however automatic recovery actually works fine according to simulator checks agains historical windshear data. Never had a reactive windshear warning in the NG, only predictive windshear warnings which usually resulted in being clear of the actual windshear.
Same here and fully agree,hence very rarely does one need to full fwd the thrust levers.
.Thanks Denti.
Wouldnt doing so also approach the EGT towards its limit or over?I know for a fact that EGT limit is not protected by the EEC except during engine start on the ground.
Using MAX N1limit should protect you from overtemp.....MAX certified engine thrust may not so..anyone has facts on this?
Sorry for the drift:8

latetonite

27th Apr 2012, 10:02

If, after take off, close to the ground, you have an actual windshear, you want to get out of it. This, IMHO is not done by selecting autopilots, verifying if the AFDS is capable of doing a good job, checking trust is not exceeding the max rated for the flight, and monitoring if the EEC`s are doing what they are designed for. Maybe some pilots might also want to check the FCOM at this critical phase of flight, and discover the "WARNING: (3 asterics) SEVERE...." at the end of the checklist, just in time before impact.
Many aircraft accidents happened where the A/C flew itself "automaticly" into the ground.
What a pilot really wants is climbing out of it and avoiding earth. This is covered in the first half of the Boeing FCOM NNM 1.11 "Windshear Escape Maneuver".
It is simply a matter of getting your priorities straight, not pushing buttons.

de facto

27th Apr 2012, 10:57

If, after take off, close to the ground, you have an actual windshear, you want to get out of it. This, IMHO is not done by selecting autopilots, verifying if the AFDS is capable of doing a good job, checking trust is not exceeding the max rated for the flight, and monitoring if the EEC`s are doing what they are designed for

AGREE mostly.
I dont think the discussion was about the decision of selecting the AP ON in a windshear condition,I cerrtainly think all would continue in a manual flight.

No need to check thrust are exceeding the max rated as you would have normally taken off with max rate (N1 limit)in the first place.(no derate/no Ass).

Only the fact to firewall automatically is an issue I hoped to discuss along with technical data that go with it.
Again we all agree,if the you aint climbing and getting closer to terra firma then firewall the bi@@@@@:ok:

captplaystation

27th Apr 2012, 15:51

You would have only taken off with max thrust if the windshear was "forecast/reported". . . but, someone has to report it, and, particularly these days where full thrust seems to be an ugly word to most companies, chances are the first guy to find it will be launching with some kind of derate.

And if it happens on approach ?

If it really is that bad, that it involves sink-rate that may exceed the performance capability of the aircraft (as it has been in the thankfully relatively rare accidents so far) I don't see much point in worrying about the engines.

EGT margin remaining won't impress the accident investigators.

ImbracableCrunk

27th Apr 2012, 16:53

No need to get crazy on these switches eitherhttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/evil.gif
Ok,if you press TOGA once,you will get the FD into GA mode and reduced GA thrust.( your FMA will read GA/TOGA/CMD) GA is reduced GA thrust,TOGA is for your pitch,and CMD is cause your AP is engaged.
When the thrust is stable, click one more time:and you will get full GA thrust(FMC N1Limit) and your FMA will read N1/TOGA/CMD.
In brief, when you see N1/TOGA, stop clickinghttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/evil.gif

I think the FMA won't change as you're still on the GA N1 limit. You're not changing the thrust limit by the second TOGA press, just how much of that mode you're getting, whether it's a thrust for 1-2000fpm or full GA thrust.

You shouldn't get an N1 indication until another vertical mode or you manually select N1.

Pub User

27th Apr 2012, 21:17

Don't forget the first push is aiming for a target Rate of Climb of 1000 - 2000 fpm; if the aircraft is in windshear and struggling to climb, the thrust will already be as high as the A/T will give, and will only back off if it reaches its target climb rate.

bigbrother

28th Apr 2012, 01:02

I just want to say that this is the first time Ive checked out the Tech Forum on this web site and I'm damn impressed at the sharing of tech views and 'hard' fact on these subjects. I have just about given up on the rest of the site for pilots slagging each other in a pissing contest. Nice work guys I enjoy the discussion.

de facto

28th Apr 2012, 03:56

I think the FMA won't change as you're still on the GA N1 limit. You're not changing the thrust limit by the second TOGA press, just how much of that mode you're getting, whether it's a thrust for 1-2000fpm or full GA thrust.

I disagree...............and does my AMM on Autothrottle system.

The FMA will read GA during the reduced thrust and N1 during max thrust.
The N1 shows you the FMC N1limit thrust is used .
You shouldn't get an N1 indication until another vertical mode or you manually select N1.

...and you will have TOGA in the pitch mode to remind you that you aint in verticle speed mode:E

I wrote this earlier but seems like it did not get much attention:to get MAX thrust with AT engaged,the second click must be done AFTER initial GA thrust is set.
So maybe you always click the dam... buttons too quickly and never got MAX thrust...hence the FMA confusion.
Just a thought:E
Captplaystation,
[QUOTE]If it really is that bad, that it involves sink-rate that may exceed the performance capability of the aircraft (as it has been in the thankfully relatively rare accidents so far) I don't see much point in worrying about the engines.

EGT margin remaining won't impress the accident investigators.[QUOTE]

I am not worried about the engines in THAT case,i have doubts in case some decide to firewall at any sign of predictive windshear or actual windshear that dont need such a drastic action......which could lead to overtemp...

Now on a pure technical note, i would be interested to know if full fwd thrust levers (max certified thrust) will provide some temperature margin from lets say the general ISA temp?

ImbracableCrunk

28th Apr 2012, 11:30

Well, here's a selection of quotes from the AMM (CL) and the FCOM (NG). It looks like the third quote backs up de facto. The FCOM is less clear (as usual). I think Boeing should have done it my way. ;)

GO-AROUND - the DFCS controls airspeed, and the A/T maintains either reduced or full GA N1.
Reduced go-around is engaged by pressing the TO/GA switch one time. A second press of the TO/
GA switch engages maximum go-around. Other modes can be selected after engines have achieved
the selected N1 limit and radio altitude is greater than 100 feet.
(3) Pressing either TO/GA switch once initiates the reduced GA mode, provides REDUCED GA
logic, sets the reduced GA latch, starts the GA timer, and arms reduced GA (maintaining).
(4) The timer (8 seconds) is reset when the N1 error is within 3% of computed N1, the reduced GA
latch is reset when the timer is reset and the GA latch is reset when radio altitude is greater than
100 feet.
(5) The reduced GA (maintaining) latch is set when the GA timer expires. It remains set until the
DFCS requests a mode change or the A/T is disengaged.
(6) Pressing either TO/GA switch a second time initiates maximum GA mode (sets the maximum
GA latch). The maximum GA latch was armed during the first 0.5 seconds of reduced GA. This
latch provides MAXIMUM GA logic and is reset if the GA latch has been reset by the timer and
altitude (greater than 100 feet R/A) and the DFCS requests a mode change (N1 or speed).
Autothrottle Modes
N1 (green) – the autothrottle maintains thrust at the selected N1 limit displayed
on the thrust mode display, including full go-around N1 limit.
GA (green) – the autothrottle maintains thrust at reduced go-around setting.With the second push of either TO/GA switch after A/T reaches reduced
go-around thrust:
- the A/T advances to the full go-around N1 limit

latetonite

28th Apr 2012, 11:32

Pub user has a good point:Your first TOGA push gives you a say 2000 ft/min climb.Think about it, if the normal associated (reduced) thrust is not enough to get this, thrust will increase to get you 2000 ft/min. I can live with that in a windshear. So no need for the second click..

latetonite

28th Apr 2012, 11:46

And just to add something basic here, in all the planes I flew before, and yes, I have/held 10 (ten) types, the windshear escape maneuvre boiled down to "balls to the wall, pitch up to about 15 degrees, or higher, up to the stick shaker if needed, in order to get out of a negative sink rate..that does it for me, irrespective of F/D or Autotrust.
This is for take off. The appoach or landing windshear escape is usual not so critical, as you have more thrust reserve available.

Cornish Jack

28th Apr 2012, 13:34

latetonite - theDallas L1011 was on finals!!

latetonite

28th Apr 2012, 18:47

Yes, that was on approach. I remember as I was training there then. But then they did not talk about microbursts yet, let alone procedures to tackle it. And I said: "Usually".

de facto

28th Apr 2012, 18:54

de facto's correct

AWESOME:E

balls to the wall, pitch up to about 15 degrees, or higher, up to the stick shaker if needed, in order to get out of a negative sink rate
Whos balls?yours?:eek:
Whats a negative SINK rate?

[QUOTE/]
Pub user has a good point:Your first TOGA push gives you a say 2000 ft/min climb.Think about it, if the normal associated (reduced) thrust is not enough to get this, thrust will increase to get you 2000 ft/min. I can live with that in a windshear. So no need for the second click...[QUOTE/].

And you have docs to prove that?
Who says you will do 2000 in windshear?,no second click?even in your negative sink?
If that is the case,it may be a reason for PONTIUS NOT to disconnnect the AT after initial GA thrust is set....:cool: