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View Full Version : 737 - A/T take-off procedure (Merged)


moscho999
19th May 2006, 12:32
Hello everybody,

I wonder how you set take-off thrust during an auto-throttle take-off (B737-300/-400/-500)
Do you, after having the engines stabilized at 40% and having pushed the TO/GA button, wait until the A/T sts the thrust by itself or do you get impatiend about the slow performance of the A/T and "fiddle" the thrust levers to the desired value.

Thank you for your help!

BOAC
19th May 2006, 12:39
Somewhere I had a Boeing brief which stresses that the setting of power is a 2 stage process, and you should NOT push them up unless the system does not work after the second stage. First stage is to about 80%ish and then the second fine-tuning. Throttle 'pushers' simply mask unserviceable throttle lever clutches and systems. I'll try to find it.

moscho999
19th May 2006, 13:29
Thank you BOAC,
I would really appreciate to have this document.
I couldn't find any references in the FCOM or FCTM.

Moscho999

BOAC
19th May 2006, 17:41
Lucky strike! Boeing Flt Ops Tech Bulletin 737-300/400/500 97-1 Dated April 29, 1997. ATA Number 22-31 Subject Autothrottle Operation. from Flt Crew Training PO Box 3707, Seattle.

Precised: First stage is to within 8% of target N1, then to target. THEN (and only then) pilots should adjust to +1% -0% of target. Avoid applying force to the levers unless manual intervention is intended. It also recommends NOT 'following' the levers such that you apply more than 1.5 lbs of force at the top or you may cause the clutch to malfunction. There is a 'caution' that more than 20kts of headwind may produce throttle hold before target is reached.

I always maintain the autothrottle should be allowed to TRY to set power or you may never know when it is malfunctioning.

junior_man
19th May 2006, 18:55
40% to spool, then about 60% let the engine stabilize momentarily there and push TOGA. Don't try to push the the thrust levers up near the target N1 and then push the TOGA buttons, it doesn't like that.

Do it that way and it will be perfect every time.

60% was necessary to get it into the active range for the PMS (if I remember correctly).

IronWalt
19th May 2006, 19:10
We should do online reviews of systems. This would be a great way to study the airplane.

Centaurus
20th May 2006, 13:28
Junior Man. 40% N1 then pushing to 60% N1 sounds like a company check captain favourite gimmick. It is best to stick to the manufacturer's procedure which is 40% then TOGA. On a non-auto throttle take off I have observed some pilots "walk" the thrust levers instead of pushing them smoothly together. "Walking" the thrust levers is another gimmick.

junior_man
20th May 2006, 15:06
Procedure was given to us by Boeing as we were seeing some issues with the autothrust. Company was operating about 80 737 300/400s back then and it was standard procedure. Also solved the problem and the autothrust worked fine. Still the same procedure today.
About the worst thing you could do was to push the throttles up to almost the target N1 and then push the TOGA button. That was a leftover habit from 737 200.

BOAC
20th May 2006, 16:04
jm - if it does not accelerate evenly from 40% snag it! BA had the Manchester fatal following long-term throttle stagger and, I believe, uneven acceleration.

junior_man
20th May 2006, 16:10
Original procedure was to hit TOGA at 40% and stable, the second step produced much better results. Especially fewer exceedances. When I left we had been doing it for about 10 years with excellent results.
Different engine acceleration may be a variety of things. JT8Ds were bad for that as they always seemed to have different bleed configurations between the 2 engines.
The big difference with the second step was to get above the minimum RPM for the PMS to start doing it's thing.

moscho999
21st May 2006, 10:12
@BOAC

Thank a lot. Found ref. doc on myboeingfleet.com.

@everybody

We changed from the 40% to the 60% procedure - but without intermittend step at 40%. Works fine for us!

Moscho999

Check Airman
8th Sep 2006, 16:49
Hi,

2 questions about jet ops:

What is the max N1 (or EPR) difference allowed before engines can be considered "stabilized" prior to application of takeoff power?

I'd also like to know when thrust is considered to be "set"? Say takeoff N1 is 100.0%, How close does the actual readout have to be before therust is considered "set"? For example, is 98.5% considered "set"?


Thanks for any help

alexban
8th Sep 2006, 17:05
As far as I know,on 737 you should set thrust at aprox 40 N1 (+- 5%) .Then increase power to be set by 60 kts.Thrust should be adjusted,if necessary,by the PM to -0% +1% target N1.
In your ex 100% to 101% N1. 98.5% is NOT good.

Intruder
8th Sep 2006, 18:53
They are both a matter of technique and tools available.

On the 744, autothrottles are generally used for all takeoffs. The thrust levers are advanced to approximately 70% N1, but that may be anywhere from 65 to 72%. The TOGA button is then pushed, and the authrottles take over.

On the 747 Classic with digital engine gauges and FFRATS autothrottles, autothrottles are used some of the time, depending on the Captain's and FE's preferences. Thrust levers are brought to approx. 70% N1, but it is more important that the N1s are consistent between engines (+/- 1-2%) than exactly 70% (the thrust levers may be significantly staggered).

If autothrottles are used, the FE tries to equalize N1 again when the autothrottles reach the programmed position, because they stop when the "leading" engine gets to target N1. He then tweaks the others ("lagging" N1) to get them as close as possible.

If autothrottles are NOT used, the Captain advances the thrust levers close to target N1, using approximately the stagger attained at 70%; then the FE sets them as close as possible to target before 80 KIAS. In this case, a little ABOVE target is preferable to below.

In either case, it is not possible to eyeball much finer than +/- 0.5% at T/O thrust.

Again, individual techniques vary.

Check Airman
9th Sep 2006, 23:09
Basically, I was looking for the N1 tolerances for the different calls, am I right in understanding from the above posts that it essentially will vary from person to person?

pakeha-boy
9th Sep 2006, 23:42
CA.....each airline has its own SOP,s,......adhere to the the one thats paying you/...

Worked for several A-320 operators....completely different SOP,s completely different reasons....the settings are either within the operating parameters or they not....:confused:

BOAC
10th Sep 2006, 09:18
Check - you may wish to glance at this thread (http://www.pprune.org/forums/showthread.php?p=2595435&highlight=autothrottle#post2595435)? Boeing (in that 'oldish' - 19/5/1997 - document, for 737 3-500, and presumably 6-900?) say initially at least 40% and no need to reduce if greater; 'Acceptable' TOGA thrust setting by a/t at THR Hold is +/- 2%, and manual intervention ONLY after the 2 stage a/t action is complete should be made to adjust to +1%/- 0% of target.

Shaka Zulu
10th Sep 2006, 13:39
My flying manual says that getting the thrust up is more important then setting them exactly the same. As far as I know there is no specific margin for that. However if the runway is slippery and a limiting crosswind I would like to make sure I'm a bit more accurate that day then normal to ensure a very even spool up time

Check Airman
11th Sep 2006, 00:54
thanks all for all the neat info

A37575
12th Sep 2006, 09:08
BOAC and Moscho 999. The Boeing Bulletin regards throttle stagger at 40% N1 during the initial spool up prior TOGA has been withdrawn as far as I know presumably because the AD's fixed the problem. Moscho - anything works fine -you just name it and it's been tried - but why not stick to the Boeing recommended procedure.?

A37575
12th Sep 2006, 09:14
There never was a Boeing published requirement to verbalise "Stabilised." Both pilots have eyes and all that is needed is to observe- not talk about it.

Elixir
12th Sep 2006, 10:49
When should the thrust be set by though? I thought it was 60knots, in which case it is often necessary to intervene as the AT second stage is sometimes too slow to reach target by this speed. A couple of times I've still been waiting for the thrust to set when we've reached 80knots - and in my company we are supposed to have "thrust set" before we call "80 knots".

EDIT: Check posts #4 and #13 in this merged thread.

Boeing Pilot
12th Sep 2006, 11:59
According to my knowledge the "Thrust set" call should be made when N1 at T/O thrust is -0% to +2.5%.
Another important issue regarding setting thrust is that if you're on a slippery rwy and hit the TOGA switch before N1 is at least 40% or if the T-levers move upp unequally you will if you're unlucky veer of the rwy.

I-2021
12th Sep 2006, 16:11
Lucky strike! Boeing Flt Ops Tech Bulletin 737-300/400/500 97-1 Dated April 29, 1997. ATA Number 22-31 Subject Autothrottle Operation. from Flt Crew Training PO Box 3707, Seattle.

Precised: First stage is to within 8% of target N1, then to target. THEN (and only then) pilots should adjust to +1% -0% of target. Avoid applying force to the levers unless manual intervention is intended. It also recommends NOT 'following' the levers such that you apply more than 1.5 lbs of force at the top or you may cause the clutch to malfunction. There is a 'caution' that more than 20kts of headwind may produce throttle hold before target is reached.

I always maintain the autothrottle should be allowed to TRY to set power or you may never know when it is malfunctioning.

Hi BOAC,

After having read this one I understand the following:p :

1)When the PF asks for T/O thrust and pushes TO/GA, the PM is not supposed to follow the thrust levers to "adjust" them to the desired N1 value until this value has been reached, or as stated in the FCTM, if THR HOLD occurs before 84 kts (or 64 kts for my dear old originals ;) ).

2) The CM1 (usually the Captain) should be waiting the thrust to be set at the desired N1 value before placing his hands on the thust levers.

Is that the meaning of the bulletin ?
Thank You :ok:

BOAC
12th Sep 2006, 16:43
Not quite, in my mind, anyway. It also recommends NOT 'following' the levers such that you apply more than 1.5 lbs of force at the top or you may cause the clutch to malfunction - the main thing is to stop the NHP 'fiddling' with the thrust levers because they do not go straight to TOGA. Very common in my last airline as a lot of the F/Os did not seem to understand the Boeing a/throttle system, giving the levers a 'shove' when they hit the first 'set'; normally going OVER TOGA at which point the a/t comes back a big chunk, and if throttle hold sets in then you can be 'short', resulting in the wrong T/Off N1 at throttle hold. It also masks u/s clutches etc because the system is not allowed to operate correctly - so you may never see the 'failures'. Better in my current airline as the Captain ALWAYS handles the throttles after button push.

Nothing AFAIK to stop anyone 'following' the levers (in fact a good idea for me) - just do not fiddle with them until you have to!:) Hands rested lightly on top is my method.

I-2021
12th Sep 2006, 17:31
Not quite, in my mind, anyway. - the main thing is to stop the NHP 'fiddling' with the thrust levers because they do not go straight to TOGA. Very common in my last airline as a lot of the F/Os did not seem to understand the Boeing a/throttle system, giving the levers a 'shove' when they hit the first 'set'; normally going OVER TOGA at which point the a/t comes back a big chunk, and if throttle hold sets in then you can be 'short', resulting in the wrong T/Off N1 at throttle hold. It also masks u/s clutches etc because the system is not allowed to operate correctly - so you may never see the 'failures'. Better in my current airline as the Captain ALWAYS handles the throttles after button push.

Nothing AFAIK to stop anyone 'following' the levers (in fact a good idea for me) - just do not fiddle with them until you have to!:) Hands rested lightly on top is my method.

Thanks a lot BOAC ! That is in fact what I usually do and seems to me also the most logical course of action :ok: