B737 WINDSHEAR ESCAPE MANEUVRE

[c100driver]

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]

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]

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]

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]

Originally Posted by de facto

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

No, not really.

[no sponsor]

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]

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]

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]

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]

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]

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]

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]

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"?

[Cornish Jack]

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!

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

[de facto]

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.

[ImbracableCrunk]

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

[lucalaz]

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.

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

[captplaystation]

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]

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]

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
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