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B737 - Setting correct Go-Around Thrust

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B737 - Setting correct Go-Around Thrust

Old 15th Sep 2010, 12:09
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B737 - Setting correct Go-Around Thrust

The FCTM states: "At typical landing weights, actual thrust for Go-Around is usually considerably less than maximum Go-Around thrust. This provides a thrust margin for windshear or other situations requiring maximum thrust".

In a non-coupled go-around where the pilot manually flies the go-around and uses manual thrust, why is it therefore that most pilots will advance the thrust levers to the GA N1 limit and perhaps call 'Set GA thrust`? According to Boeing the actual thrust needed for GA at typical landing weights, is considerably less than max GA thrust.

.

The pitch up associated with max GA thrust is significant - indeed under certain circumstances if the pilot fails to control the pitch up with prompt use of elevator and stabiliser trim, instances have occurred where aircraft have stalled.

The problem appears to be that the definition of what is sufficient GA thrust is hard to judge. You need a definate N1 to aim for. In the case of an automatic pilot GA using autothrust, the autothrottle commands thrust sufficient for 1000 to 2000 fpm climb rate. From memory that is around 75 -85 percent N1 on most occasions.

The question I have is how does a pilot judge what N1 should be the target in a manual go-around. Seems to me it is a matter of personal opinion and the local check captain's opinion wins every time if you want to avoid an argument on a check flight in the simulator. But who is really right?
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Old 15th Sep 2010, 12:25
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'Go around, flaps 15!'
*TO/GA push
*Push thrust levers forward by strechting your arm.
*(Aim for 85% N1)
*Follow flight director. If you have a climb rate less than 1000fpm, increase thrust. If you have a climb rate exceeding 2000fpm, reduce thrust. Or leave it where it is if satisfies your goal. Eg. if you only need to climb 1000ft, you can also do with 800fpm ROC... But usually 85% N1 will give you a good rate.
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Old 15th Sep 2010, 12:49
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Approach with AT in ARM, press TOGA and AT takes care of the rest (one click for reduced G/A thrust, two for full). SOP for the last 20 years here, approved by Boeing if necessary training is done.

Of course if someone has everything off aim for 85% N1, that usually gives a good value as reivilo mentioned.
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Old 15th Sep 2010, 13:36
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Denti could you explain in short the sequence during a manual approach? At what moment and how would you arm the autothrottle with F/D off and on?
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Old 15th Sep 2010, 13:53
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A37 - it was, under the CAA IR, a requirement that full N1 be used for a non A/T g/a - I don't know where EUOPS sits on this. That is why it has 'traditionally' been so, since the factors the A/T uses to calculate 'sufficient' g/a thrust are not available to a pilot.

Most Ops Manuals have (should have) a para which says "when a safe rate of climb has been established the N1's may be reduced to avoid excessive climb rates etc etc" or words to that effect. In other words, g/a N1, flap, gear up, throttle back.
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Old 15th Sep 2010, 15:37
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reivilo, whenever we go to manual flight we just deselect SPD so that AT is in ARM mode. A more complicated method is to click it off on the thrust levers and command the switch set to arm again, that one is not really used though.
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Old 6th Oct 2016, 13:16
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Full Go-Around Thrust Perferfomance

Hi, I've got a question I can't find an answer to.

B737NG FCOM says: A/T (if armed) engages in GA and advances thrust toward the reduced go–around N1 to produce 1000 to 2000 fpm rate of climb...With the second push of either TO/GA switch (if A/T engaged and after A/T reaches reduced go–around thrust):
• the A/T advances to the full go–around N1 limit"

The FCOM does not say what kind of performance the full go-around N1 limit should give, for eg at max landing weight, what kind of rate of climb should we expect?
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Old 6th Oct 2016, 15:31
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The FCOM does not say what kind of performance the full go-around N1 limit should give, for eg at max landing weight, what kind of rate of climb should we expect?

I can't answer wth specifics ROC, but I would assume it will be enough to satisfy the minimum required climb gradient %. That is the real performance target rather than ROC.
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Old 6th Oct 2016, 15:53
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The Boeing OPT works out whether you can meet a minimum climb gradient (with single engine) as required by the approach chart. This will keep us clear of terrain if the GA is executed per procedures as stipulated in the charts. My question is not really concerning terrain clearance. I just need an idea what the full N1 GA thrust could provide.

Also related to the above, what controls the value of the reduced GA N1 thrust and what %N1 value exactly is this? Unfortunately the Boeing FCOM does not explain any of these...
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Old 6th Oct 2016, 17:13
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Reduced GA thrust will be up to full thrust, it tries to maintain a VS, not an N1.
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Old 6th Oct 2016, 20:17
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One push of TOGA

On a 737-800 gives 8% climb according to maintenance manual.
Will get page number soon.
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Old 11th Oct 2016, 05:42
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Found it...finally!

Section 22-31-00 pg 86

There are two A/T go-around modes, GA and N1. For reduced thrustgo-around the A/T uses an internally calculated thrust value to achieve an eight percent climb gradient.
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Old 11th Oct 2016, 08:11
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On a 737-800 gives 8% climb according to maintenance manual.

Just the sort of thing an engineer needs to know, but not the pilot.

Over the past 30 years the FCOM's have been diluted extensively. There have been many legitimate questions asked by myself, in the bath, or by students in the class-rooom. No answer in pilots' FCOM, but there they were in the non-accessible maintenance manual. Go figure.
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Old 11th Oct 2016, 08:24
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Originally Posted by Denti
...whenever we go to manual flight we just deselect SPD so that AT is in ARM mode.
This is so useful and easy to use the auto throttle in 'armed' mode.
Sadly, within numerous operators (or in the case of a certain red nosed outfit, their Dublin version), misunderstanding of the concept of how the autothrottle works, and failure to read a particular memo correctly, have resulted in explicit instructions not to use the speed off function.
Sadly, some management types who rarely fly, have too great an input on this. Thus proving that an over abundance or reliance of rigid SOPs are actually not in anyone's best interest.
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Old 11th Oct 2016, 08:29
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On a 737-800 gives 8% climb according to maintenance manual.
Interesting information, as the FCOM only tells the pilots that the first push of the TOGA button gives a rate of climb between 1000fpm and 2000 fpm.
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Old 11th Oct 2016, 16:55
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Interesting information, as the FCOM only tells the pilots........

Like I said; the manufacturer treats the sharp end jockeys like trained monkeys. Just tell 'em what to do & when, not often the why. No wonder training standards have followed the same trend down to trained monkey levels.

'C/A to pax, "would you like some nuts?" pax, "what do you think I am, an monkey?"

'Pax to c/a."do you serve nuts?" c/a, "we serve everyone, sir."

'pilot to c/a, "it's my birthday, may I have a banana with my coffee, please?"

'c/a to pilot, "€4 for the banana ,sir."

OMG, how cynical. Sorry. I'll go and out the cork back in the bottle. Goodnight.
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Old 12th Oct 2016, 02:43
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The "AT in ARM" has been discussed numerous times.

There are LIMITED times when cannot/shouldnot be used, primarily extremely gusty wind conditions (so maybe 5-10%?? of approaches).

In ARM the thrust lever is a totally manual operation until either:

- the PF stuffs up and allows airspeed to decay towards stickshaker
OR
- TOGA is pressed then the AT will schedule 1000-2000fpm of positive climb, full GA thrust if pressed again.

It is a SAFETY enhancing feature...and SAFETY's meant to be a good thing.

All the above can be briefed then demonstrated in the SIM so everyone "gets it".

Sadly the "flat earthers" seem to have greater numbers - proving in this case that greater numbers do not automatically mean the correct idea/answer.

Cheers.
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Old 12th Oct 2016, 07:28
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This is one of those debates where there really is no one right answer. In a perfect world (where we do not continually fly with new copilots) arm is a useful safety backup. Ironically my experience with the new guys is that they tend to get confused when the autothrottle kicks in in gusty conditions and the approach can then quickly become unstable. As pilot monitoring you are one step further removed as your hands are not on the throttles. Sods law is you will be switching to tower look up and see the speed all over the place. In Denti's Air Berlin (who of course no longer operate the 737) the level of experience in the right seat was actually a lot higher than somewhere like Ryanair. So it really is horses for courses and this is just my personal preference having tried both ways over many years.
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Old 12th Oct 2016, 09:46
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Fair enough - however if properly covered in classroom and SIM then maybe the decision NOT to use arm due extremely gusty conditions should be a crew decision made earlier in the approach?

Simply cannot understand how there can be any justification for decreasing safety 90-95% of the time for a - maybe - difficulty 5-10% of the time.

Has the ability to demonstrate and train really decreased that much??
Or are pilots today all "rote good, thinking/understanding bad"??

Cheers.
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Old 12th Oct 2016, 10:27
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One issue is that you only know how gusty it is on approach after the event. The atis and tower winds often bear little resemblance to the winds at a thousand feet.

The arm mode is extremely useful in missed approaches, but statistically I have gone around way less than 1% over the last ten years as a captain on the 737. But co-pilots chasing the speed is pretty much a daily occurrence. It is usually way too high rather than too low, which is a problem if you operate to shorter runways regularly.

Equally relying on the auto throttle to dig you out of trouble is not foolproof as the Turkish airlines crash in Amsterdam demonstrated.

I would have no problem with being told we should try and use arm more. But based on my experience I still prefer all off or all on for the 737.

The point about rote learning is a interesting one. New pilots have to learn the SOPs and apply them. It is only after they have gained enough experience that they can understand why they are doing something.

Some of our guys think they know a great deal more than they really do when released to the line. The reality is that a decent level of experience is about 1500 hours by which time they often have something bigger and shinier in mind and move on.
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