737NG A/T and A/P Go-Around

[N1 Limit]

Can anybody please elp with this,i'm sort of confused between A/P and A/T Go-around mode which one works when and how?sometimes i read A/P Go-around is armed below 1500FT when VOR/LOC and G/S are engaged and on the other hand it says A/T Go-around is armed below 2000 feet.I need someone to clarify that to me please.Thanx

[highdownwind]

F/D go-around is armed below 2000ft, if A/T is armed it will drive the thrust levers for you.
An A/P go-around is available below 1500ft if both autopilots are engaged with g/s and loc captured.

[N1 Limit]

Thanx very much for your contributions it zas quite helpful to get the mental picture of the matter,i appreciate

[Callsign Kilo]

A/T go around mode is armed below 2000 RA and above 2000 RA when G/S captured or flaps not up I believe. You can see this displayed on the thrust mode annunciator above the N1 gauges. The autopilot or flight director does not need to be engaged as this is purely an A/T function.

Should the AFDS (A/P + FDs) and A/T be disengaged, flight director guidance is available upon pressing TOGA. However the engagement of further role and/or pitch modes require the flight directors to be recycled to on.

As said, below 1500 RA and with FLARE ARMED annunciated on the FMA, a dual channel go around (both A/Ps engaged) is available. The A/T should automatically provide go around thrust upon pressing TOGA. After all, you should not be shooting dual channel approaches without an A/T - well certainly in my airline anyway!

If you are new to the aeroplane remember that if the A/T has been disengaged; pressing TOGA will only activate GA guidance on the FDs. You will need to set GA thrust manually (around 85-90% N1 - NOT the green N1 reference bugs as these relate to the full go around N1 limit and would be what the A/T would set if you pressed TOGA twice with the A/T engaged). I know this sounds silly, however I have seen this happen so often in the sim with guys new to type.

Good luck :ok:

[BOAC]

A couple of points for UK operators, Kilo - (not sure where you operate):

A/T is NOT required for Cat III on a 737.

I think you will find that the regulations REQUIRE setting full power on a 'no A/T' g/a. The only time a reduced power is allowed is with a single TOGA press, A/T engaged.

[shlittlenellie]

BOAC can you back up the last bit? Satisfying the G/A climb gradient would be the only regulatory requirement and with two engines that will usually and easily be satisfied at reduced power.

[BOAC]

Came to me years ago from a pedantic (but no doubt correct) TRE. The 'first push' gives a fixed thrust setting which can be factored into any limiting weights. Setting an 'unknown' manual thrust setting cannot. I don't know if it is writ somewhere ( I guess it will be in some dusty tome) but it is basically common sense.

[Callsign Kilo]

Thanks BOAC, some interesting points

Unfortunately an inoperative A/T precludes CATIII approaches with my lot; although I respect the fact that it may not be necessary for auto-coupled approaches on the 737. In my case I refer to the 738.

In reference to setting full GA N1; I believed that the S.E. MACG of 2.5% (in case of a CATII approach) became the limiting factor? In my airline it is taught that in most cases no greater than 90% N1 is a necessity for a manual go around. This aids the controllability of the procedure. Obviously additional thrust is available and this is trained as an obvious consideration to make under particular ambient conditions.

[Denti]

CAT III requires A/T in my operation, CAT II doesn't. There is an exception though, if equipped with a serviceable HUGS you can fly it completely manual, no AP and no A/T. We don't have that toy therefore A/T is required at all times for CAT III, no matter if dual or single engine.

[EW73]

Gentlemen...

In the 737-700 I'm familiar with, the first push of the TOGA button...

"advances thrust toward the reduced
go-around N1 to produce 1000 to 2000 fpm rate of climb."

...not as mentioned earlier, a specific thrust setting.

You will get whatever thrust is required to get and maintain 1000 to 2000 fpm rate of climb.

Cheers... :)

[sevenstrokeroll]

wouldn't it be loverly?

go around? pull up, push throttles up and off you go

so much easier than all this magic stuff

and, have you ever seen one throttle go up and the other just sit there/?

[Capt Chambo]

wouldn't it be loverly?

go around? pull up, push throttles up and off you go

Pretty much exactly what you do in the Airbus. ( And some people say it is overly complicated!)

[Sciolistes]

You will get whatever thrust is required to get and maintain 1000 to 2000 fpm rate of climb.
I can't find anything to say that it will provide whatever thrust is needed to achieve it. I used to assume that until I read BOAC's post and then I started to look. It seems to me that 1,000 - 2,000 fpm is a pretty wide margin. If somebody said to me that the Boeing engineers figured out a narrow reduced thrust range that would achieve that for all normal conditions then I could accept. Also, it says somewhere that it will maintain pitch until RoC increases and then maintain speed, which also suggests a fixed (or near enough) thrust.

I don't know and really Boeing seem to have decided that we don't need to know how it achieves it, just what to expect and what to do if it doesn't happen.

However, clearly then manual thrust less than GA thrust is not unknown so long as you are achieving 1,000 fpm! Personally, I just push them forward and then get the PM to set it to the bug.

[Capt Chambo]

I can't find anything to say that it will provide whatever thrust is needed to achieve it. I used to assume that until I read BOAC's post and then I started to look. It seems to me that 1,000 - 2,000 fpm is a pretty wide margin. If somebody said to me that the Boeing engineers figured out a narrow reduced thrust range that would achieve that for all normal conditions then I could accept. Also, it says somewhere that it will maintain pitch until RoC increases and then maintain speed, which also suggests a fixed (or near enough) thrust.

A lot of the answers to these questions can be found in the FCOM, Automatic Flight, Go Around & A/P Go-Around. (In my book it is 4.20.16)

[BOAC]

...not as mentioned earlier, a specific thrust setting.

You will get whatever thrust is required to get and maintain 1000 to 2000 fpm rate of climb. - I apologise for sloppy (simplified) wording in my post - the meaning of the first push 'fixed thrust setting' was that required to give a known (minimum) performance - 'fixed' in as much as it could be taken as 'enough' to guarantee a minimum performance (hence full 'TOGA' engine out). This aspect of 737 ops has always been one of my 'dark' areas in as much as I have 'assumed' (but never been assured!) that the limiting approach weights based on required g/a gradient have been calculated on the engines achieving that 1000fpm at max take-off weight.

Perhaps JT/baritone/FE Hoppy etc can throw some light on this (personal) conundrum and explain why we cannot simply apply g/a thrust manually with A/T not engaged so that we produce that (mimimum) 1000fpm?

[Johnny F@rt Pants]

have you ever seen one throttle go up and the other just sit there/?

Yes - Auto-throttle clutch failure. It's easy to replicate in the simulator, next time you're in there get your instructor to show you.

[nick14]

Does a thrust lever split not cause the A/T disconnect?

Im with Kilo on this, im guessing were from the same company. If the A/T is engaged then a single push of TOGA gives you 1000/2000 fpm ROC, after they have started to advance a second push gives you full beans.

On a manual GA we are advised to set 90% as this gives more than sufficient thrust without giving too much and causing the aircraft to go screaming through the flap speeds and MAA.

[BOAC]

On a manual GA we are advised to set 90% as this gives more than sufficient thrust without giving too much and causing the aircraft to go screaming through the flap speeds and MAA. - don't dispute that in the slightest as a practical solution, it is just that had this particular TRE 'tested' you you would have 'failed'!

To complete the 'wise words' given to me - you MUST use full power on a manual A/T g/a and THEN once you have established a safe climb you can set 90%.

[sevenstrokeroll]

johnny fart pants

I've had the one throttle move the other just sorta sit there in both the sim and the plane.

I just think that the simpler the plane, the less problems with it....the head engineer at Douglas had a sign in his office: KISS...keep it simple stupid

[ImbracableCrunk]

It's interesting that Boeing uses "ensure/set go-around thrust" for a go-around and for an engine failure during go-around, they use "[v]erify maximum go-around thrust is set."

Couldn't one infer that during a go-around, you don't need to set "maximum" go-around thrust if flying manually? Or is Boeing saying something like, "Let the A/T do it's thing - or manually set maximum go-around thrust."

[nick14]

Thats an interesting viewpoint and I can see both sides.

Iv had it twice in the a/c and both times the A/T disengaged due to the split.

[K_9]

nick, I'm curious--at what point does the A/T disconnect? How much of a throttle imbalance?

[Capt Chambo]

If the A/T is engaged then a single push of TOGA gives you 1000/2000 fpm ROC, after they have started to advance a second push gives you full beans.

Not quite, you need to wait until the reduced N1 has been reached before you press the TO/GA button if you want full GA thrust.

From the Boeing 737NG FCOM. (My bolding)

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.

[Callsign Kilo]

nick, I'm curious--at what point does the A/T disconnect? How much of a throttle imbalance?

A thrust lever split of 10 degrees and greater rings a bell, however not 100% on that.

[McBruce]

10 degree split is correct.

[nick14]

Ah apologies, so after the thrust is set a second push will give you full beans.

It happened to me a while back watching one move and the other stay static and then the switch clicked off and the flashing red light warned us of the disconnect. I much prefer real life examples other than reading about them. You learn much more.

Cheers

[N1 Limit]

Thanks very much Callsing Kilo