B737 Autothrottle....yet again

[galdian]

DISCONNECT/DESELECT

Know this has been well discussed over the years, sometimes a question pops into ones head that looks at things from a slightly different angle.

I was trained, and have used for a long time, the DESELECT mode to retain alpha floor and G/A thrust protection; others swear black and blue that Boeing is totally "all auto or all manual" so must DISCONNECT and lose those protections.
No doubt there's a large middle ground.

I've tried to work out an answer to a question - and I can't, maybe some "black and blue swearers" can provide enlightenment.

Why would Boeing include - and continue to include as standard - on the 737 Autothrottle the DESELECT mode......if it's never, ever, ever to be used??

[DoktorZoom]

I'm one of those black and blue swearer
Could you please state where exactly boeing "include as standard" the use of A/T DESELECT?
Just one manual...bulletin...reference would be fine! Then we can discuss further...

[Centaurus]

The FCTM says: The AT Arm mode is normally not recommended because its function can be confusing. The primary feature the AT Arm mode provides is minimum speed protection in the event the airplane slows to minimum manoeuvring speed. Other features normally associated with the AT such as gust protection are not provided. Some malfunctions that affect manoeuvring speeds cause the AT to maintain a speed above approach speed.

In the simulator when some pilots hand fly but with the AT engaged, it is most annoying (to the passengers down the back as well) to see and hear the continual pitch changes and engine noise changes as the pilot tries to maintain level flight for example. If his manual flight is rough due lack of practice or more likely lack of flying ability then the AT works like a drovers dog - always moving. It means sloppy flying.

Boeing test pilots must have researched the manual flight/AT Arm combination and decided for technical reasons that manual flight means AT off except under certain periods of flight. But check pilots often have a personal preference and teach that preference as gospel rather than accept the Boeing advice. Personally I prefer to stick with the advice of the manufacturer. Particularly in a court of law.

[latetonite]

If I remember well Boeing changed their filosophy into "auto Pilot Off, Auto throttle off " about ten years ago. There was an AD for this. Apparently there were some incidences where during flare, the AT just inched a bit forward, and the story ended in a long landing.
It now results in funny go-arounds, as the Throttle has to be manually set by one of the pilots.
"TOGA, flap 15" gives you a nice FD, but that is all.

[galdian]

Doktor and Centaurus

You miss the question: why do Boeing continue to have the option...if it's never, ever, ever to be used??

Could reduce the cost of a Boeing 737 by a $$ or two for a "simpler" on/off autothrottle.

Centaurus - generously - by stating the FCTM statement that is not NORMALLY recommended demonstrates that those who have deseigned and built the aircraft (Boeing) have it there for a reason.
He also has indicated problems that have been observed - by pilots who have not been properly trained by a training department.

The question remains: why do Boeing continue to have the option...if it's never, ever, ever to be used??

[DoktorZoom]

Well...one thing is to have the option, (which is by the way NOT RECOMMENDED), and one thing is to have it "included as STANDARD"
I think latetonight is right...some years ago it was possible to fly the approach manually with the A/T deselected. You had to be aware the during the flare, there is no gust protection and the risk is either a hard landing or a go around. After a few accidents things changed.
Since nowadays manuals are written by lawyers Boeing decided to leave the deselect mode available but suggested not to use it.
Therefore now its use is NOT STANDARD.
This means you can use it but if "something" happens...during landing,you will have to explain yourself why you did something NOT RECOMMENDED by the manufacturer.

[galdian]

Doktor

Appreciate your response and see your points, however:

- the latest FCTM I have indicates not NORMALLY (yes that word, NORMALLY) recommended which so many arbitrarily seem to not see;

- the same questions remains: why have the option...if it's never, ever, ever to be used??

With regards to being able to, years ago, fly with A/T DESELECTED and working great: you can still do this (done it for 24 years, so far no problems) with proper training and understanding.
Why, in this day and age anyone would want to NOT use functions that assist/improve safety I will never understand.



Sadly your statements regards Boeing and legals probably true - until you ask why it's safer to disconnect alpha floor and G/A thrust automation??
I thought the first dictum of every airline was "safety".

Personally - only because I was properly trained about the system and have had no problems for 24 years - I'll keep using DESELECT until the flat earth society finally catches and executes me!

Seriously appreciate your comments, probably I just can't understand why procedures/safety go backwards when with a little training it can be maintained/improved.

Centaurus

Maybe talking at cross purposes but A/T DESELECTED is manual flight, if the PF doesn't adjust the thrust levers then thrust/airspeed don't change- for better or worse!
Totally agree - A/P turned off with A/T still engaged is non Boeing and can (probably will) turn into a fight.

A/T deselect is a manual mode...and may just save your ass on a dark and stormy, min circling approach if you get "distracted" or have to do a G/A.
Call me crazy - I reckon that's good use of the available systems.

[Denti]

Im working for one one of those companies that still use the ARM feature as SOP. We have been using it now for over 20 years on both the classic and the NG and so far it has never caused any landing problems. It can be a nuisance in approaches during gusty weather, most of my colleagues click it off in manual flight then. Guess most of us have read the turkish airlines incident and one thing often pointed out as the main reason was the AT behaviour with less than 27ft RA indication: going into retard mode, not shoving in more thrust to maintain speed. Wonder therefore how those long landings really developed. Flare at 50ft? Anyway, good training remains one of the major issue, no matter which SOPs are used.

[ImbracableCrunk]

FCTM

The FCTM is not regulation. My airline probably does more than one thing in direct contradiction to the FCTM, but those methods are in our SOPs and approved by the governing body.

SOP and approved makes it regulation.

[edit - My company doesn't use ARM. I was talking about other things.]

[FlyingStone]

Originally Posted by galdian

The question remains: why do Boeing continue to have the option...if it's never, ever, ever to be used??

1. It wouldn't be very practical/safe to make such a drastical change in configuration, given that some companies still have this as SOP (and they don't crash on every single flight) - and Boeing decided that they will try to lower training cost by expanding the 737 type rating to MAX. So every change they make, the pilot still has to be able to safely fly on both MAX and the oldest -300 you can find.

2. Nowhere does it say it's forbidden to deselect A/T, it just says it's not normally recommended. It's a feature that could be useful, like CWS - you wouldn't use it during normal flight, but it's a nice thing to have.

[RAT 5]

It now results in funny go-arounds, as the Throttle has to be manually set by one of the pilots.
"TOGA, flap 15" gives you a nice FD, but that is all.

Sounds exactly like a manual G/A.

I've not used this 'deselect' option, so please may I confirm something: if you deselect A/T on approach are manual thrust changes still available? If they are then I see its use as making no difference to the piloting technique, even in the gusty flare. From reading the comments it seems like a safety net. It is too many moons since my departure from B757/767 to B737 family. I seem to remember B757/767 having such a mode. When I went to B737, along with many other former B757 pilots, there were those who investigated the B737 auto-throttle and decided it was possible to configure it like a B757. The CP & HOT, who neither had B757 experience, poo-pooed it with Boeing's blessing, so they said.
"Not normally recommended," does not mean "thou shalt not...". If it was a 'thou shalt not' by the manufacturer then perhaps it should not be possible at all.

[Denti]

if you deselect A/T on approach are manual thrust changes still available?

Yes, If the AT is deselected (put into ARM mode) you have to use the thrust levers just like in total manual mode. AT will automatically activate in a few cases though, like approaching a level off altitude or getting close to bug speed with a speed trend for even less speed. That can be a bit, well, non-intuitive during approach in gusty conditions as it will activate well above Vref given a sufficient large trend, but in all other conditions it adds low speed protection which is simply an added safety net.

As said above ARM is simply a manual thrust mode, so keep your hands on those thrust levers, which means you can immediately counter any non-wanted thrust input should AT activate at the wrong moment.

[DoktorZoom]

"SOP and approved makes it regulation"

Totally agree on that. If your company wants you to use it...no big deal.
Just be sure whoever is flying with you is trained on it and understands its limitations.

[RAT 5]

I've always been intrigued how the whims of a CP, in so many different airlines, that makes it gospel. They can't all be correct. Why don't people operate the equipment the way it was designed? However, Boeing have changed many things over the years after feed-back from operators. They do the job day in day out in a spectrum of circumstances. SOP's should be a living thing, but still it is often the whims, without too much rhyme or reason, that make a mess of it. Oh for the simple life.

[latetonite]

Setting the trust levers in a go-around, with the AT disconnected, is a two pilot job. PF initiates the Go Around, and FM has to adjust GA trust, as this is difficult for the PF during the pitch and configuration changes. Unless this is specificly briefed, a once-a-year go-around with two random pilots serving as a crew usually results in an interesting exercise, where at least something is forgotten, done late, or not done at all.
With the AT armed, the go-around takes less effort, as it only requires TOGA, following the FD and selecting Flap 15.

In my humble opinion, deselecting AT in approach makes life easier for many pilots.
In case there would be an inadvertent trust increase in short final, pilot still can disconnect at all times.

Main thing, as always, is understanding the system, and knowing how to use it.
Limited knowledge of SOP's only is looking for trouble, especially during unforeseen go-arounds. There is a well known low cost operator in Europe, where all go-around actions are briefed in detail before every approach.

In other places, most go-arounds become some sort of single pilot operation exercises.

[Lord Spandex Masher]

Setting the trust levers in a go-around, with the AT disconnected, is a two pilot job. PF initiates the Go Around, and FM has to adjust GA trust, as this is difficult for the PF during the pitch and configuration changes.

Then PF needs more training.

[de facto]

T will automatically activate in a few cases though, like approaching a level off altitude

I am quite sure this is not correct.
The Arm mode will only activate as a speed protection if the aircraft actual altitude is BELOW the MCP altitude.

[ImbracableCrunk]

The Arm mode will only activate as a speed protection if the aircraft actual altitude is BELOW the MCP altitude.

Altitude? How about some references?

[Denti]

Might be a customer option of course, god knows boeings option is quite long. Ours however do activate the AT shortly before level off, shove in a bit of thrust, then deactivate back to arm to activate again at level off. One can prevent that by putting in a bit of thrust oneself of course, same on level off.

[Rick777]

Another reason for keeping the feature is standardization across fleets. I haven't flown a 737 for 20 years or so, but I do know that in the 777 the auto throttles are pretty much only disarmed in response to an abnormal procedure. At least by Boeing procedures. As has been mentioned a lot of operators have their own way of doing things.