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?

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!

Thanks, your answer sounds correct to me. :8

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.

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?

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

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.


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.

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

Really?and how does the 'machine' responds differently in each case?

Please explain..
Once to get initial pitch guidance,but twice to get max limit thrust.
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.
Not a boeing procedure.
Not a boeing procedure.

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

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.

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.

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.

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?

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?

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

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 :)

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.

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.

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.

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.

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 ?

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.

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.

Pontius,

Send you a pm.

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.

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'.

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?

Quite a steep descent there.. 2 deg from an upset recovery..
B737NG:RA= AP+AT OFF.

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

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.

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?

Windshear Escape Manoeuvre
 

..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!

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:

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:

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 :)

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

@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.

grounded27

No.

Next question.

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:

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

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.

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.

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

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!

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

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?