B737 A/T use during approach and G/A.
 

Good evening,

I am in the need for some clarification.
I am curious to know how the SOP's of your respective companies handle a manual approach and go-around on the 737NG or MAX.

Correct me if I'm wrong here:

During an approach, if a manual landing is planned, the PF should disconnect A/P and A/T at the same time. Upon disconnecting the A/T (by pushing the A/T disconnect switch on either thrust lever), the A/T arm switch on the MCP trips to OFF, and automatic thrust is no longer available during the go-around.

If a go-around is required, the PF will therefore need to manually establish go-around attitude and set go-around thrust.

So, my questions are:
1. Should the PF manually establish full go-around thrust (as depicted on N1) or set a reduced go-around thrust, and if so, what is the target N1 for the reduced go-around thrust?

2. Boeing QRH Man. chapter states that the autopilot can be engaged as needed for a manual go-around, but does not say anything about the autothrottle system. As I understand it, the A/T should be manually re-engaged on the MCP during the go-around. At which point should that be done?

3. After pressing TO/GA, the AFDS will engage in the go-around mode. If an A/P is engaged at that time, will the pitch mode stay in GA? And, shouldn't the A/T be armed at that time as well to comply with Boeing recommendation to either be fully automatic or fully manual.

I may be on the wrong path here, but would really appreciate some help regarding this.

Hello Viking, It seems to me that you are A fresh B737 Pilot and that’s fine and I hope...in any case I suggest you at least to check and study the Flight crew training manual, It will help you to understand.

1. Set whatever N1 the orange bugs indicate. If that's too much take a bit off.
2. At any point after the AP is engaged will do.
3. No it'll go to MCP speed. Nothing wrong using manual thrust with the AP engaged. Just don't forget or you'll end up with an overspeed or worse.

Orange bugs ?

Sorry, that's a 300 thing. Whatever colour they are...green!? Can't remember!

Green, eco friendly color ;)

Viking,

Speaking as a newly minted 737 guy myself...take a step back from the notion that Boeing recommends fully automatic or fully manual. They have backed off of that considerably. My employer uses a HUD to hand fly CAT III approaches with the A/T engaged.

There is no practical reason to disconnect the A/T when hand flying. Although the purist in me prefers it otherwise, the simple truth is the A/T works quite well and will retard at 27 feet...or it is supposed to, anyway. In the meantime, you can manipulate the throttles as needed, including manually retarding them earlier than 27 feet if the situation warrants.

If you disconnect the A/T via the throttle buttons, you will have to set GA thrust manually. Remember that the first push of the TOGA button will cause an engaged A/T to target whatever thrust is necessary for a sedate 1000-2000 fom go-around. The second push of TOGA gives you max GA thrust. I suspect that the N1 bugs will only display max GA thrust; I can't find any reference otherwise.

For a good discussion of how not to manage a go-around, see the UK AAIB report on G-THOF at Bournemouth on 23 Sept 2007. This was not an NG, so there are some difference, but it is quite an eye-opener.

As always, regardless of what anyone on this Forum says, follow your own operator's SOPs! :)

You are asking for trouble if you are flying half manual half automatics in the 737. It is untidy and can cause unwanted pitching movements as the AT tries to maintain the selected speed. If Boeing recommend a procedure - in this case turn off the AT if manually flying except for the climb - then only automation dependant pilots will balk at the recommended procedure. That is usually because they lack the self confidence to hand fly without the crutch of an autothrottle engaged. :=

FCOM VOL.1 11.41.31 describes the N1 Limit page in flight and its associated indications. The bugs will be/can be set at the different maximum values for CRZ, CLB, GA and CON.

FCTM 1.37 Autothrottle Use gives some pretty straight forward guidelines on the use of the A/T. Just KISS.

Thank you :ok:

Hand flown CAT III with A/T engaged? Talk about making life hard! Manual thrust with a HUD is a walk in the park. I've never heard Boeing recommend this.

There is a very practical reason to disconnect the A/T when hand flying, which is why Boeing recommends it.

If a go-around is required, the PF will therefore need to manually establish go-around attitude and set go-around thrust.

So, my questions are:
1. Should the PF manually establish full go-around thrust (as depicted on N1) or set a reduced go-around thrust, and if so, what is the target N1 for the reduced go-around thrust?
There will be differing opinions. I know there are some who insist on full power then reduce, once established with gear up, if applicable. There are others who suggest to do the same as the automatics i.e. single TOGA. This gives 1000-2000fpm and satisfies relevant performance requirements. How much? I find 85-90% is more than satisfactory. If will be aware of your LDW and so can choose a number in that range. It needs briefing as PF needs to advance the TL's manually and then call "set thrust". I've seen it so often in the sim where PF sets a good reduced N1% and then PM shoves it up to full. Causes a little surprise and a WTF moment. This assumes both engines thrusting.

2. Boeing QRH Man. chapter states that the autopilot can be engaged as needed for a manual go-around, but does not say anything about the autothrottle system. As I understand it, the A/T should be manually re-engaged on the MCP during the go-around. At which point should that be done?
Same time as AP. There is a difference of opinion which comes first. Boeing changed the sequence order a few years ago. Check your SOP's & FCTM.

3. After pressing TO/GA, the AFDS will engage in the go-around mode. If an A/P is engaged at that time, will the pitch mode stay in GA? And, shouldn't the A/T be armed at that time as well to comply with Boeing recommendation to either be fully automatic or fully manual.
FMA's will change to the same as pressing LVL CHG. Some operators have SOP's to fly manually until Flaps UP. There is an idea that coming out of GA and into MCP SPD is detrimental to the GA profile. Not sure why they think that as you would most likely delay AP engagement until you are relaxed, in trim and probably 1000' & climbing. For A/T engagements see #2.

RAT5,
I want to ask you a question about the Go around full and reduced!
We did notice this time, later better than never..lol...that during a Go Around when Derated and/or combination with ATM, pushing Toga gaves You just a reduced thrust fpr just that engine rate so, we used to push Toga twice!
Here my question...is that a single clue of the SIM, or that is what is happening in real in some 737, and I did not notice till now!

One push of TOGA will give you thrust for 1000-2000fpm. The second push gives you full TOGA.

Chesti not sure if it was a reply for me or not...
anyway I do know that one push gives you a reduced 1000/2000FPM and second gives you a full Thrust...
I asked something else...
if you derate the engine to 24K for istance, what will happen if you push TOGA once?
It will give you Reduced Thrust for that engine rate, 24K?
AsI notice in the SIM, this is what happen, so the needs to push always twice Toga!
hence my qestion if that was just a particular "issue" of the SIM.

We did notice this time, later better than never..lol...that during a Go Around when Derated and/or combination with ATM, pushing Toga gaves You just a reduced thrust fpr just that engine rate so, we used to push Toga twice!

I don't understand this. Derated & ATM are Takeoff thrust settings not GA thrust settings. TOGA on a GA is a reduced thrust from full GA to give 1000-2000fpm. That thrust will vary e.g. heavy weights, hot & high airfields, tailwinds. It doesn't matter if the engine is limited to 22K 24K 26K or higher. V/S is there parameter monitored and the EEC will command what is necessary. Why such a wide spread in V/S? No idea, but I assume that 1000fpm will handle all GA performance parameters with ease, and so this was a chosen minimum.
Is full GA thrust on a 22k different to full GA on a 26K engine? I suspect it might be because operators will choose 26K and high MTOW for their network. It would be a sad day if you returned for an overweight landing on 1 engine and wanted to make a GA, but sank slowly onto terra firma anyway. I don't know it for a fact, but I suspect it.
Either way, whatever engine 1 xTOGA should give minimum 1000fpm on the a/c. If the sim doesn't then I'd investigate with the engineers.

Probably the worlds most valuable forum post ever, second to this one of course... :rolleyes:

+1
Really helpful.