B737 WINDSHEAR ESCAPE MANEUVRE

[Denti]

@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]

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

[latetonite]

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]

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@@@@@

[captplaystation]

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]

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

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]

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]

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]

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


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
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]

de facto's correct

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]

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]

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]

latetonite - theDallas L1011 was on finals!!

[latetonite]

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]

de facto's correct

AWESOME

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?
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....

[Shaka Zulu]

Its Boeings non normal manoeuvre philosophy: all in or all out
Tcas all out
Gpws all out
Windshear auto: all in
Windshear manual: all out after toga so f/d guidance

To/ga in Windshear on an auto manoeuvre will give you full rated thrust if it's required to get to 2000fpm. The system copes admirably and flies the stick shake better than I could.

However there are 2 notes in the QRH:
1. maximum thrust can be obtained by firewalling the thrust levers if it's required. It's part of the p2's actions when terrain contact is imminent.
2. Severe Windshear might be too much for the afds to handle so be prepared to disconnect

[lucalaz]

In the manual scenario why do we need to press toga before disengaging the A/T?

What if the A/T was already OFF when windshear is encountered?

[Shaka Zulu]

Depends on how you have switched the A/T off. If you have switched them off with the A/T Arm switch on the AFDS pressing To/Ga will not wake up the autopilot.
However having disconnected the A/T with the disconnect on the throttles themselves pressing To/Ga will give you To/Ga thrust and also F/D guidance.

You are required to press To/Ga on a manual windshear go around because you want Windshear Guidance from the Flight Director (F/D). Pitch to 15Deg initially and then further up with the F/D (as per the QRH drill)

[Denti]

However having disconnected the A/T with the disconnect on the throttles themselves pressing To/Ga will give you To/Ga thrust and also F/D guidance.

As we are talking about the 737 that is as far as i'm aware not the case. You will get F/D guidance in certain cases, but thrust will still be manual.

[ImbracableCrunk]

As we are talking about the 737 that is as far as i'm aware not the case. You will get F/D guidance in certain cases, but thrust will still be manual.

Yep. Off is off. There is no "pop-up" autothrottle.