Why is 2000 fpm initial rate of climb on auto GA
 

B737. On an auto go-around, pressing TOGA normally gives you a lower N1 than normal GA thrust since initial rate of climb is set at 2000 fpm.

However, on a manual throttle go-around it is normal to push the thrust levers to full GA thrust since the exact N1 to maintain an initial rate of climb of 2000fpm is not tabulated anywhere.

If it is considered "safe" to apply normal GA thrust in a manual GA, then why on an automatic GA with AT engaged, does Boeing used reduced power to maintain 2000 fpm rate of climb when full GA thrust is happily accepted for a manual GA?


After all, during a manual GA the PF opens up the thrust levers and says "Set GA thrust". And the PF does just that. He doesn't fiddle the books (thrust levers) to set 2000 fpm rate of climb.

Hi Tee Emm,

From the FCTM:

"At typical landing weights, actual thrust required for a normal go-around is
usually considerably less than maximum go-around thrust. This provides a thrust
margin for windshear or other situations requiring maximum thrust. If full thrust
is desired after thrust for the nominal climb rate has been established, press
TO/GA a second time."

As for the thrust setting during a manual go-around. In our company we do not need to set maximum go-around thrust with both engines operating. Only a single engine go-around requires us to set maximum thrust. Maybe it's a company thing?

Makes me think about low capture altitudes, red and amber captions coming up due to available speed of stab trim versus ROC during an auto go around Tee Em.

obb

Hi Tee Emm, Why would you require any more?... ATC has probably only cleared you to 3000ft anyway, to do a circuit and second attempt.

Because climbing at 6,000 FPM is a bit much...

Tee Emm, I suspect it's all to do with the difficulty of manually setting a lower than full power throttle setting. I don't fly the 737, but if as you say there are no 2000ft/min N1 figures anywhere, it's easier to just set full GA power and concentrate on flying the GA itself.

On two engines, it is obviously desirable to climb at reduced power and this is therefore designed into the automatics. Given that automatics are the preferred method of operation these days, Boeing assumes that they will be used on a GA and so have built in the 2000ft/min first press.

Good one, FSF.

Wow!

With both autopilots engaged for an auto-land, the 737 starts trimming for the flare below 350-400' and with that trim setting and max GA thrust the autopilot would not be able to control the pitch me thinks :eek:
That's why :ok:

Next time you are in the simulator try closing your eyes and setting what you think is a reasonable go around thrust. On the 737-800 the relevant number would be about 88% N1 at a normal landing mass of around 63 tonnes. Keep practising until you develop the " muscle memory" for the correct N1. Then when you press TOGA, advance the thrust levers and call " Go Around Flap 15 Check Thrust" or whatever your SOP calls for the PM will only have to make minor adjustment if any to the N1 to achieve the desired performance.

A common SOP on the 737 was to set full g/a thrust on a manual g/a but then you were permitted to reduce to ?not less than 90%? when the vs was upwards. Solved all the perceived problems.:ok:

FCTM says: At typical landing weights, actual thrust required for a normal go-around is usually considerably less than maximum go-around thrust.


Boeing don't define "considerably less." Is that for instance, 10% N1 less than full GA thrust? Or, maybe 5%N1 less? Seems awfully vague which is possibly what the OP was getting at?


So what do you tell the PNF? How about: "Going Around - Set 10%N1 less than max GA thrust, please old chap and while you're fiddling with the thrust levers, you may as well give me Flap 15."

See previous?

Well, Boeing doesn't define the N1 as that is demand scheduled and can actually reach full G/A thrust if required. It is scheduled to give between 1000 and 2000 fpm climb rate, with an aim to reach 1500 in an ideal case. That is availalbe whenever the AT system is active, for those airlines (like the one i'm working for) that use the ARM mode it is available in manual flight as well, thus precluding any requirement to figure out any thrust demand for oneself. However it ain't hard to do it manually if needed, just aim for around 1500fpm fly the aircraft.

Denti:


That's easy for you to say. :)

What is the problem with full power, g/a flap, gear up and then set 90%?

TWO ENGINE GO-AROUND/VISUAL CIRCUITS
 

I do lots of SIM and BASE training in a 767.I always brief the trainees to mimic the Automatics in both cases.Manually set approx. 1.25 EPR (Full EPR is 1.45).On a G/A reduce to this once you are CLIMBING.On a circuit, set this thrust once clear of the ground and say 2-300 feet aal.Works very well on any Jet, and keeps the handling "under control" makes the flying easier therefore SAFER.Ball-park numbers only.

Its a great piece of design and most welcome with a low altitude level off on a missed approach.

I have never flown the 737NG but with a single TOGA push for a go-around, do you not get the same target N1 setting display?

Is it old steam guage displays or a CRT screen for engine displays?

G/A again . . ?
 

Again, we have this subject, will no one (A320) heed my pleading call . . ?


(which is) Assume you are going around in an A320, at night, Temp+10 degrees Weight 62tons. and Select 190kts and keep F1, level at G/A altitude, stay Selected and drive yourself around the circuit/circle/procedure/to the hold/back on the approach/or atc/ whatever to put you back into the approach . . .slot - bringing the speed back to 180 when level since you have retained your F1 on the flaps.


Versus


Toga, still in Nav G/A - - - - where does this take you - whats your speed, where did that speed come from? I am sure there is an SOP for a G/A but in Automatic City, what is it? How many of you do the whole thing in Selected (whether manual or A/P)? Is it horses for courses, meaning - can Captain A do it his way and Captain B do it her way? - as both ways being equally effective and safe.

Other than in the sim I have never pushed TOGA because you scare the hell out of everybody for no reason. I just added climb power smoothly and did it manually. I know the new school is push a button and hang on.