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Old 24th Apr 2012, 13:13   #1 (permalink)
 
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B737 WINDSHEAR ESCAPE MANEUVRE

I refer to the Windshear Escape Maneuvre included in the Boeing 737 QRH NON-NORMAL MANEUVRES section.

If the maneuvre is flown MANUALLY (A/P and A/T OFF) with only F/D guidance available, Boeing say to aggressively apply maximum thrust whereas in the AUTOMATIC case either TOGA switch need to be pressed and verify thrust levers advance to GA power.

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?
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Old 24th Apr 2012, 13:23   #2 (permalink)
 
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It doesn't matter, the first push establishes a 2000fpm climb rate. If you are in windshear the engines will automatically go to full power to try and achieve that. That goes for autoflight. In manual flight pushing the toga switches will activate the windshear escape mode of the flight director, the auto throttles do not move and hence you have to push them full forward yourself.

Edited, red the QRH, last statement was incorrect!
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Old 24th Apr 2012, 13:45   #3 (permalink)
 
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Thanks, your answer sounds correct to me.
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Old 25th Apr 2012, 05:32   #4 (permalink)
 
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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.
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Old 25th Apr 2012, 05:44   #5 (permalink)
 
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Quote:
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?

Quote:
, 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?
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Old 25th Apr 2012, 05:57   #6 (permalink)
 
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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.


Quote:
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.
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Old 25th Apr 2012, 05:57   #7 (permalink)
 
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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
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Old 25th Apr 2012, 06:28   #8 (permalink)
 
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Quote:
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?

Quote:
it's gone to great trouble to produce a great big 'WINDSHEAR' on your TV for you
Please explain..
Quote:
Therefore it is only necessary to push the TOGA switch once
Once to get initial pitch guidance,but twice to get max limit thrust.
Quote:
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.
Quote:
why disengage the A/T in manual flight once max thrust is set.
Not a boeing procedure.
Quote:
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?
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Old 25th Apr 2012, 06:37   #9 (permalink)
 
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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 Edited bit: I now see what you meant about A/P & A/T off....see explanation below....boy I'm cocking this thread up

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.

Last edited by Pontius; 25th Apr 2012 at 06:49.
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Old 25th Apr 2012, 06:48   #10 (permalink)
 
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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.
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Old 25th Apr 2012, 07:04   #11 (permalink)
 
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Quote:
Quote:
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.
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Old 25th Apr 2012, 07:16   #12 (permalink)
 
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Quote:
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?
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Old 25th Apr 2012, 07:37   #13 (permalink)
 
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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?
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Old 25th Apr 2012, 07:43   #14 (permalink)
 
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Quote:
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?

Quote:
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
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Old 25th Apr 2012, 08:04   #15 (permalink)
 
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Quote:
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.
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.
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Old 25th Apr 2012, 08:14   #16 (permalink)
 
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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.
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Old 25th Apr 2012, 08:15   #17 (permalink)
 
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Quote:
Originally Posted by pontious
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.
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Old 25th Apr 2012, 08:17   #18 (permalink)
 
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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.
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Old 25th Apr 2012, 08:18   #19 (permalink)
 
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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 ?
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Old 25th Apr 2012, 08:28   #20 (permalink)
 
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Quote:
Originally Posted by capt~ps
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.
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