B737 - Setting correct Go-Around Thrust

[A37575]

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?

[reivilo]

'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.

[Denti]

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.

[reivilo]

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?

[BOAC]

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.

[Denti]

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.

[cruisercruiser]

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?

[RAT 5]

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.

[cruisercruiser]

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...

[Denti]

Reduced GA thrust will be up to full thrust, it tries to maintain a VS, not an N1.

[stator vane]

On a 737-800 gives 8% climb according to maintenance manual.
Will get page number soon.

[stator vane]

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.

[RAT 5]

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. :confused:

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.

[Lancelot de boyles]

...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.:ugh:
Sadly, some management types who rarely fly, have too great an input on this.:D Thus proving that an over abundance or reliance of rigid SOPs are actually not in anyone's best interest.

[Denti]

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.

[RAT 5]

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.

[galdian]

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. :ok:

[lederhosen]

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.

[galdian]

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. :ok:

[lederhosen]

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.

[galdian]

lederhosen

Thanks for your comments/observations, appreciate what you're saying about more modern times, after 27 years still believe ARM mode is the way to go and don't believe it's that hard to achieve with appropriate groundschool/SIM training.

However understand how things have changed for the "children of magenta line" generation where cutting costs necessitates a certain dumbing down where rote is more important than understanding or even more important than the "why doesn't this feel right/something's not OK" feeling that older pilots sometimes get or, equally, sometimes just some basic and simple aeronautical commonsense says "this ain't as it should be".

Certaintly ain't like the good old days!!

Cheers. :ok:

[Centaurus]

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.


I can't see the problem. The Boeing 737 FCTM advice could not be more clear. My version states: "Autothrottle use is recommended during takeoff and climb in either automatic or manual flight. During all other phases of flight, autothrottle use is recommended only when the autopilot is engaged in CMD."

Forget the why's and wherefore's. if Boeing had to provide a technical reason for all recommendations in the FCTM, the manual would be double the size.

In addition, the FCTM has this to say under Autothrottle ARM mode.

"The autothrottle ARM mode is normally not recommended because its function can be confusing. The primary feature the autothrottle ARM mode provides is minimum speed protection in the event the airplane slows to minimum maneuver speed. Other features normally associated with the autothrottle, such as gust protection is not provided."
............................................................ .....................................

Before the above advice was published, you can bet Boeing test pilots have conducted measured tests on the various autothrottle systems before final recommendations are published. Yet one wonders what causes pilots to think they know better than the experts at Boeing:(

[RAT 5]

Certainly ain't like the good old days!!

Indeed; if thinks don't change they stay the same. Trouble is the change should be an improvement, but sadly.................

Regarding the A/T in ARM. I seem to remember this was the case on B757/767. I think those with experience of this possibility investigated/experimented and discovered it was possible on B737's. Every B737 operator I flew with, CL & NG, banned it. I see Boeing uses the phrase "not recommend". I remember an old SOP manual of mine which had a list of definitions: e.g. should not = must not = forbidden". "not recommended" = is not the normal method but is not forbidden.

So what does Boeing really mean? Denti tells us that Boeing 'approved' its use in his airline. Presumably that was at customer's request. That would suggest it is not forbidden.
In my B737CL days an RA was disconnect A/P and follow avoidance guidance. Then came NG and it's SOP, which then filtered down to CL models, was to also disconnect A/T. The reason being was to comply with the philosophy of All ON or All OFF. It was not a technical necessity, yet the 'experts at Boeing' decided it was better: not from an airmanship or technical point of view, but from a pedantic philosophy point of view. It has been discussed previously and some have said there are gotchas if you leave it in. I've also seen, in the sim, many serious gotchas after it was disconnected. Personally I preferred the earlier method. Disconnecting A/T is recommended and thus became an SOP; but it does help to understand the why's & wherefore's. But as has been mentioned elsewhere we are treated too often and too much as naughty children who should do only as we are told and not to question. However, when needs must we are supposed to act using the best solution for the unexpected scenario; except that ono-one had written that one down yet.
Agh!

[galdian]

Centaurus
Always enjoy your posts spoken with bags of expreience; may not always agree but certainly enjoy.

So either remove the switching outright or train pilots to understand how to use the system - not rocket science.

Simple "yes or no" answer:

"For pilots appropriately trained using the AT in ARM mode, when conditions permit, increases safety".

Yes or No??

.....awaiting all the incoming "maybes" by those who can't RTFQ or are terrified by having to think.

Cheers. :ok:

[RAT 5]

Surely someone from Boeing is available to give 'the horses mouth' answer. Centaurus claims the Boeing test boys have made this 'not recommended' decision, but yet they approve some operators to do it, or some just do it anyway.
It would be useful to understand, and therefore accept or not, the blanket statement of not recommended. It would also be educational; not a bad thing in this day and age. It would give a more in-depth knowledge of how the system works and what its short-comings are. Too often we barely scratch the surface with knowledge and just do as we are told. Then some rebel decides to experiment because it seems a possibility and good idea, and the system (which ever one) bites you in the backside: and then you discover why it was a 'do not'. Unbeknown to us button pushers on the outside there were some hidden gremlins lurking on the inside that a manufacture hadn't the time to fix and so did not want them woken up.

The days when an old friend of mine was a L-1011 captain in early 80's and pilots had a semi FE training are long gone. The FE had been replaced by buttons whose systems are interconnected via strange unknown routes. QRH's have replaced trouble-shooting manuals. Pilots play the piano at their peril. The memory of a tea & biscuits moment on a B767 when the A/T would not engage on takeoff. Captain climbed out and when well out of the TMA decided to reset the A/T cb. It still didn't work, but the RAT deployed and they returned. Oops!

[lederhosen]

My latest FCTM also says not 'normally' recommended, which leaves a little leeway. I have worked with Boeing approved procedures for the 737 where we pressed arm and now where we do not. Both have pros and cons, bit like Airbus Vs. Boeing, but we won't go there!

[galdian]

Philosophy from Boeing in the good old days was:

- proper airline, able to properly train, educate and demonstrate then using the AT ARM mode no problems;

- airline unable to train properly or maybe first jet into an expanding airline etc then maybe KISS better, all completely on auto or all completely manual.

Cheers! :ok: