Gums, I beg your forgiveness, because I'm not very smart. What does your "basic view of A/T"(which you admit yourself you don't entirely understand) have to do with the SLUF?

@ Flyboy

Simple, we duplicated the AT function that Bloggs, et al describe for cruise. But we did it by using the available steam gauges. So an AT would have been nice on our longer missions.

Our TF-41 was the first fan for a single-motor jet in USAF, and it behaved differently than the pure turbojets the others used, although the Vaark had fans.

Well it's really not that complicated. It may seem complicated when you try and put it down in words and you do need to have an understanding of how the auto-flight systems work, but it's a piece of piss, and it is a nice tool to have. I wish all of our aircraft had it.

The 717 is my only auto throttle system experience. It's so easy to use that the only down side that I can see is that one loses the ability to set power manually & intuitively. We're not encouraged, in fact actively discouraged from, turning the AT off and keeping the hand in. From the perspective of the 717 I can't see why it seems so hard.

Including a suggestion to add an SOP for FMA change callouts! ;)

PS: Wouldn't "Thrust" indicate speed was being controlled by thrust, not pitch, as appears to the case in your example?

Agreed. Gums, trust the people who actually use this stuff in their job (I assume, from your posts, that you don't). It has improved safety no-end and is p155 easy to operate. BUT, one must be ready (and able) to notice stuffups and to fly it manually! If you're not, you're Turkish/AF447 dead. Unfortunately, that is where the bosses of the industry are pushing us.

I take your point that it's easier to use than describe. I have an understanding of the systems being an ex avionics eng...:). I can understand using them in other phases of flight but looking at it personally I wouldn't want to let a machine control the speed on approach. I only fly GA so don't have to worry about having it on or not as there's not that choice to make. I just like to think I have some instant control over things when I'm near the hard bits.

As pax on commercial flights I'm always slightly apprehensive on approach as I know that the best of us can have a switch pigs. I just hope that someone on the deck is keeping a beady eye on the IAS.

Well we let the autopilot control pitch and roll on the approach. We fly with hands on yoke and power levers though so can always make instant corrections if required.

I'm not au fait with modern autothrottles (obviously!) but if you have the AT controlling the approach speed what happens if you command more thrust? Does it let you move the throttles or do the throttles move but when you take your hand of them they try and restabilise at the commanded speed? In otherwords if you need a handful of go and need to manouvre hard both hands say to avoid another aircraft will it still try and go back to the command speed?

Manouvering hard during a go-around? Shouldn't happen or ATC didn't do its job in the first place. If something gets in the way it is a go around which on my tiny boeing means i will press the TOGA buttons upon which the autopilot will fly the go around path (both laterally and vertically) and the AT will produce enough thrust for a low climb rate of 1500 to 2000fpm or full climb thrust if i click the buttons a second time. If already flying manually the same is gonna happen, except that i will get flight director guidance only with the same thrust settings (we use the ARM feature, otherwise thrust would have to be set manually).

Reading other contributors, it seems one big issue is "mixed operation" - manual flight with automatic thrust. Like Denti, I fly the baby Boing (738). It is either all manual flight or all automatic. We fly short haul with regular short legs so are in fairly recent hand-flying practice. I am still in the RHS and the 73 is the only airliner I have flown so bear that in mind when listening to my opinions.

When disconnecting one, you generally disconnect the other, though I have flown occasionally with the AT inop but used the autopilot (RVSM requirement). Unlike Denti's company, we do not use the ARM mode in manual flight (that is a debate involving plenty of religious schisms in itself!) so for a go-around in manual flight one just stretches out the thrust arm, sets a fixed thrust level and sticks both hands on the control column. When manually flying the 73 one is very aware not only of the speed but the thrust set - even if the speed is good, a glance at the N1 will tell you if you need to add or reduce thrust in short order before you get any observable trend.

The difference is in the Airbus/777 where it appears the SOP is AT use through touchdown, which I can see could lead to a lack of awareness of actual thrust, and losing it I'm your scan while simply controlling the flight path.

I fly approached A/P off A/T on all the time. Works peachy.

In what type if I may ask? FBW or conventional controls?

Thanks for the replies, most interesting. When I did my IMC rating and was doing NDB holds and approaches, (if you've ever flown those in a light single in actual bad weather and crosswind you'll know they are interesting...) my instructors day job was 747 pilot. I said to him in the gaps where I actually had the capacity to speak 'What's this like in a big jet then?' 'Oh I just press a button' he said. Git.

Bloggs,

Yes, THRUST mode is speed on pitch, power is either idle or CLB, depending vertical direction. We do call out the FD modes, but not being an airline, not obsessive about it, just when the mode shown is not expected.

E-170/175. FBW, except for ailerons.

Thanks, Okie, a good point about engine failure for a twin or even a four-motor plane.

I recall the DC-8 training flight at MSY back in 1967 or so during a "simulated" two engine approach. What would an AT do if you got a little slow?

I also like Okie's observation that you fly years with the AT, but then when airmanship counts, you can't or should not use the AT.

I have to fall back and lurk, now, and let the heavy folks contribute. but before I go....

We lost two folks in the A-37 during single-engine go-arounds( not practice, but battle danage or basic failure). The big motors caused the plane to act more like a "conventional" twin versus "centerline" thrust. One motor put out 50% more than BOTH motors on the T-37!! So even with plenty of power available, you had better get the ruddder in early and not cram the throttle forward. Otherwise, you began a roll and could not recover unless you eased forward and got the yaw under control. At high AoA, the thing acted like a swept wing jet, and roll-due-to-yaw was about the same.

@ Bloggs....... My perspective on flying AoA developed when I started in the SLUF ( A-7D). Being a Navy design, our approach was the slowest you could fly depending on weight with gear and flaps down. it was "draggy". I soon found that you had better get the power in early if pulling up a bit for glide path or to maintain the AoA you were supposed to use. I doubt if an AT would have helped much, but maybe it would have. My other jets were less sensitive to AoA and I flew the basic power for speed, and used AoA to confirm the manual's calculated speed. I would have liked the AT for cruise to optimize mach, but it wasn't a big deal to retard power a bit to maintain optimum mach.

and so I return to the lurk mode.

Dave Smith
 

but if you have the AT controlling the approach speed what happens if you command more thrust?


The way Boeing A/T works, throttle position always equates to thrust command. There are friction 'brakes' the connect the throttle levers to the autothrottle drive - if you don't like what the A/T is doing or want to override for any reason, it takes ~2.5 lbs. force at the knob to make the brake slip and move the throttle independent of the A/T (i.e. ~5 lbs. total for a twin or ~10 lbs. for a 747-400/-8).


Now, once you override the A/T, unless you disconnect the A/T (button on the thrust lever) the A/T will continue to try to drive the throttle so you'd need to continue holding the thrust lever.


This is pretty much common across the Puget Sound built Boeing aircraft.


Clear enough?

That makes sense. Must be Canadian! In a real aeroplane that would be PITCH mode.

The speed, obviously, will not reduce because the autothrottle is holding it there, like the cruise control on your car. You don't put your foot on the accelerator when you start going up a hill, do you?

Why you'd want to slam on the power/go a lot faster to avoid another aeroplane is also a bit of a mystery. In any case, as soon as you started pulling (or pushing) in your dogfight, the AT would change the power to maintain the speed.

And yes, if you really need to override the AT, you can do so; just push or pull the throttles as you want. As soon as you let them go, the AT will set the power to achieve the speed target. And you can easily disconnect the AT if it goes ape on you.

It is becoming more apparent to me that the 737 is the only airliner where it is recommended to disconnect both, and that seems to be because of the pitch-power coupling. There is absolutely no problem flying around with the AP out and AT in in other types (in mine, recommended), provided you monitor the speed; in fact it is a damn-sight easier to do visual manoeuvring handflying with the AT in than out.

No it doesn't.

Yes I see your point in a big jet that has plenty of reserve power and a large speed range. I keep relating it to flying SEP's, my bad.

Bloggs

Well, PTCH is vertical FD/AP mode, THRUST an autothrottle mode associated with FLC FD/AP vertical mode. Not sure, but not very different from Seattle ideas.

Know what you are drinking
 

Something we pilots love is the fact that we never live two times the same flight. Had anybody here another experience ?

Automation & systems (what I call "butterfly") at the contrary work only with something that physicists call models, who are math algorithms. Math algorithm mimicks reality, but like some sodas mimick whisky, it is not whisky, it is not the reality. The pilot is mandatory to adapt the model to the reality and use safely the best usable mode to do the real flight.

The NTSB Dec 11. 2013 enquiry shows that Asiana SOPs and pilots trust only in math algorithms not very well adapted, and ignoring some situations like the loss of the glide !

That airline, these pilots have no ability to adapt their real flight to the infinite situations of flight always different, always new.

Butterfly can only do some very specified tasks.

Granma story
 

Hello Gums, please return from lurk mode.

To answer your original question, I apply the old adage, to try to explain it in such a way, that your granma would understand it. Following is the way I explained it to my son when he was in flightschool.




AUTOFLIGHT

A summary for the subject assignment Autoflight.

In this assignment, a lot of terms are used, that may cause confusion if they are not properly explained: autopilot, flight management, autothrottle, autothrust, flight guidance, flight control computor, flight control panel, flight control unit, etcetera, etcetera.

An autopilot is a simple apparatus, that can somewhat fly an airplane.
An aircraft is controlled through the use of elevator, ailerons, the rudder and thrust. Furthermore there are (leading and trailing edge) flaps and speedbrakes.

Autopilots normally provide only control with the elevator and ailerons, they have a pitch channel and a roll channel. In exceptional cases they may also provide yaw control with the use of the rudder.
The control of the gas (thrust / jets or power / props) is managed by the autothrottle (or autothrust), nomenclature is more a matter of taste of the manufacturer. There is a certain relation between autothrottle and autopilot functions, but that can probably not be called real cooperation.

The flaps (and slats), speedbrakes and landing gear are never controlled by an autopilot, all configuration changes are made manually by the pilot.


AUTOPILOT

Basically an autopilot performs only some very simple functions:

Attitude hold - the attitude is maintained (pitch and/or roll)

Steering towards a certain value -

Pitch/ maintaining an altitude
a speed
a rate of climb or descent

Roll/ maintaining a heading (Heading Hold)

steering towards a heading (Heading Select)

Furthermore there are complicated modes whereby steering is based on the deviation of a radio signal, for instance pitch for following the ILS Glideslope and roll for following the ILS Localizer. Also the final phase of the autoland function is complicated – signals from the radio altimeter are used to flare the aircraft and accomplish an acceptable touchdown. On the runway nosewheel steering is integrated to stay on the centerline of the runway.

A factor that can complicate the picture, is the description of what happens at the moment that the autopilot is engaged: that is not necessarily during a static situation, it can also be during a dynamic situation.

Let’s say you select Heading Hold during a turn – during the rollout of course the heading will change a little bit. Should the autopilot now turn back to the heading that existed at the moment of engagement, or should it continue on the heading that exists at the moment of wings level (which could be defined as reaching a bank angle of less than 5 degrees)? That sort of “submodes” of course is described in the documentation.

For a mode such as Heading Hold, it is not necessary to set a value anywhere. Of course, a source of information is needed (for instance the Inertial reference System).

For a mode such as Heading Select of course it is necessary as pilot, to set the desired heading. That is accomplished with a knob on a panel that is usually located near the windscreen (within reach). The name of that panel is again a matter of taste of the manufacturer – Mode Control Panel (MCP) or Flight Control Unit (FCU). It is also possible to let the desired heading be determined by the navigation system. The autopilot is then “controlled” by the Flight Management Computor, or the Flight Guidance System, or whatever name they have given to the equipment. The mode will then have a name like NAV (Navigation) or LNAV (Lateral Navigation).

The pitch mode will normally work in conjunction with the autothrottle. Note specifically that I do not say that they cooperate – they work each in splendid isolation, but their functions are selected in such a way, that there is a logical relation.

The gascontrol can operate in a thrust mode or in speed mode.
In thrust mode, a certain level of thrust is maintained (e.g. take-off thrust, but idle thrust is also possible).
In speed mode, thrust is varied as needed to maintain a certain speed.

The pitch control can vary the pitch attitude to maintain a certain altitude (or a specific rate of climb or descent, or even an ILS glidesope, in other words, the vertical value), or it can maintain a certain speed (that is an horizontal value).

The inter relation now is as follows: when the pitch control steers towards the vertical value, then the autothrottle takes care of the speed.

When the autothrottle maintains a certain thrust, then the pitch control will take care of the speed.

In that way, altitude changes are taken care of: when you are flying at a certain altitude (pitch in altitude control and autothrottle in speed mode) and you want to climb, then autothrust goes to thrust mode and increases to climb thrust. Simultaneously, pitch mode switches to speed mode. The increased amount of thrust will want to accelerate the aircraft. Pitch control will react by pulling up the nose, executing its task to maintain speed constant. As a result, aircraft will climb.
When approaching the new desired altitude, the functions are swapped again: pitch will maintain the altitude and autothrottle must maintain speed constant. Because pitch will have to decrease attitude in order to maintain altitude, speed will increase when thrust remains at climb thrust. So, autothrust will reduce thrust in reaction to the level off by pitch control.

Of course you will read about “altitude capture modes”, those are temporary modes for the transition between the level change mode and level flight. The autopilot will calculate a nice transition between those two phases and tries to fly that as smoothly as possible, otherwise you get rough movements and sick passengers.

The mode names again depend on fashion: Altitude capture is annunciated by one as ALT CAP, by the other as ALT*

The setting of speed can be done by the pilot, with a knob on the glareshield panel (MCP or FCU), but can also be delegated to the Flight Management System. That sytem can maintain pre-programmed speed restrictions in Standard Instrument Departures (SID’s), or the standard limit of 250 kts below 10.000 ft. During the climb, economic climb speed, depending on the entered cost index; at altitude, the desired cruise speed, based on cost index and actual wind conditions, etcetera.
The name of the pitch mode again depends on the fantasy of the manufacturer – VNAV (Vertical Navigation), CRZ (Cruise), or PROFILE, you name it.

For descent the operation is as during the climb, only then of course, the autothrottle will choose idle thrust.

There are also somewhat more complicated level change modes – for relatively small altitude changes it is possible that the autothrottle will go to a sort of half gas value, this in order to prevent extreme thrust changes (jet engines suffer most from large temperature changes of the hot components).
Boeing for instance has the Flight Level Change mode (FLCH), where the thrust computer calculates approximately what thrust is needed to reach the new altitude in 2 minutes. If it is for a climb, then of course for a large altitude differential you will run into the climb thrust limit; if it is for a descent, then for a large altitude differential you will reach idle thrust. In case of large altitude differences, of course you will need more than 2 minutes, but in case of small altitude changes (1.000 or 2.000 ft), you will achieve that the engine life is spared and the flight movements are smoother.

For the descent there also is a sort of PROFILE mode: the descent is then flown in principle with idle thrust, but programmed altitude and/or speed restrictions in the arrival route will then be respected.
In that way, it is possible that on certain stretches, the autothrottle will increase thrust above idle, when the “desired” segment is too flat for an idle descent at the desired speed.
Complicated? For instance, when approaching from Germany to Amsterdam, waypoint NORKU (on the border) is restricted to BELOW FL280, speed 280 – 300 kts. Later on, at the TMA boundary, BELOW FL100, ABOVE FL070, speed 250 kts. At ILS interception point NOT BELOW 2.000 ft.
It is also possible that a segment is so steep that, with idle descent, maintaining the path leads to an increase in speed. It is possible that the system than advises with a message “DRAG REQUIRED”, or it may even anticipate the problem with a message “TOO STEEP PATH AHEAD”. What you then do as a pilot is up to you - perhaps you have the bigger picture that everything will nicely settle without any fuss, perhaps those messages open up your eyes that action is necessary, anyway, as stated earlier, speedbrakes are not under the authority of the autopilot.

Note that all the modes that have been mentioned, are indicated on the Primary Flight Display, just above the Attitude Indication in the so called Flight Mode Annunciation (FMA), green letters, every change highlighted by a box drawn around the change for some 10 seconds.

Some snags are possible for the unwary. Mostly those snags are in the combination of manual flight and autothrottle, but not all.

The autopilot calculates what it would do, when in control of the aircraft. With the A/P in command, it does as it calculates and as long as all systems are serviceable, A/P and A/T do a nice job of flying the aircraft, if need be, from shortly after take-off all the way to rollout after landing.
When the A/T is tits up (case, almost stall of Thomson at Bournemouth), or when it is OK by itself, but fooled by another system input (case, crash of Turkish at Amsterdam), then you will see that the A/P happily maintains ILS Glideslope, with nobody taking care of the speed.
When all systems are OK, but the pilot does not check that he has selected the correct mode, then you may see the aircraft happily tracking down the ILS at ever increasing speeds, rather than starting the Go Around, when the pilot has increased the thrust manually, but failed to trigger the Go Around mode and failed to notice the Flight Mode Annunciation that still is in LOC G/S !!! (multiple occurrences of Air France at Paris De Gaulle with anything from A-320 to B-777.

When the A/P is not in command, its calculations can be shown as output of the Flight Director – if you follow the pitch and roll steering commands of the FD, then you will follow the path that the A/P would have flown.
Remember, the division of tasks is the same as described for the A/P modes – A/P and A/T swap roles, but they work in splendid isolation. If you do not follow FD commands at a time that A/T is in a thrust mode, actually nobody is taking care of the speed !!!

A/T may have a bottom function to kick in regardless when angle of attack reaches a threshold value. This function may surprise pilots and also, the pitchup effect may exceed A/P authority if the A/P had trimmed to a very aft setting in the attempt to maintain G/S at a very low speed (case, Thomson at Bournemouth, even though thrust selection there was associated with Go Around).
The just mentioned A/T protection feature may also be defeated by the A/T being in THR HOLD mode – a situation that may be associated with FLCH mode: after the A/T has set the calculated thrust value, it disconnects or goes dormant to allow the pilot to set a different amount of thrust without having to constantly fight the A/T.
Note that THR HOLD is annunciated in the FMA !! This gotcha got the Asiana crew.

Bottom line
– take note of what the aircraft is telling you
- monitor what the aircraft is actually doing (e.g. speed)
- take action if you don’t like what is happening

With regards gums, to your question about use of AoA (indicators) in commercial big jets – here is a reference to an excellent article on that in the Boeing AERO magazine, edition 2000 quarter 4, find it via link
AERO

As the edition is already quite old, the text and pictures are not anymore collated, but it still is well worth the effort to retrieve and read it all.

With regards to your questions about use of A/T in engine out situations – depends on make and model and also on what options companies have been willing to buy into. Sometimes engine out means manual thrust only certified, sometimes A/T and Cat 3a ILS to autoland is still certified.

Use of rudder in engine out case – same deal. Some aircraft provide yaw control with rudder always, some rely on manual rudder until multiple autopilots are engaged for a coupled approach.

Reaction of aircraft also depends on whether FBW or not – if engine out causes yaw, then roll coupling will occur in non FBW system, but counter aileron (and skidding flight) is result in FBW system.

Hope this will clear up matters for you a bit, just post if any questions remain.
Check six.

Edit - only some layout items

Holy MCDU, AirRabbit has a brother!

Interested to learn that the 737 is one of the few medium aircraft that recommends manual thrust in manual flight. Strikes me as no fun flying with the AT engaged!

There is more food for thought on the autothrust complacency in another Air France approach to stall on Avherald.

This one obviously not just to do with autothrust (10° NU in landing config :ooh:) but another one to add to the discussion.

Like moths to the light, they all look at the runway... :ouch:

I don't like the term complacency. That crew were not complacent; they were out of their depth.

Gums had better not read that report; he'll say it confirms we're all nuts saying what a wonderful system the autothrottle is! :eek: :}

Air France approach to stall Tel Aviv
 

I posted this during discussion on the autothrottle thread on Tech Log, but deserves a wider audience:

Avherald - Air France A320 approach to stall

I don't fly the Airbus so the stuff on mode manipulation is lost on me slightly, but 10° NU pitch in the landing config is pretty scary :eek:

Again, with an AT supposedly engaged, nobody was looking at the speed!

(re AF incident at Tel Aviv) There's more to it than just dumb use of A/Thr
 

Yes, not nice, but I thought the most interesting bit in the report might be this (end of para 3.4):
Which roughly translates to:
I would go further, the rearward heave on the side stick showed that the PF simply hadn't a clue about how the C* control law worked in pitch, and that she thought she was still flying a conventional aircraft aircraft like a 737. She ALSO didn't understand the concept of thrust versus speed modes of the A/THR, but it is hard to know which is more egregious.

Later on the report says:
With respect, it shows a lot more, just as the investigation into AF447 showed a lack of knowledge that went far beyond the stall warning system, basic instrument flying for a start. But the world, FAA, EASA, ICATEE et al, is reacting to the bits the BEA noticed, not the ones they missed.

The moral is: on the A320 NEVER disobey the FD pitch bar in OP DES mode, particularly if you are relying on A/THR to control speed (it won't, because it will be in IDLE mode).

When you no longer want to obey the pitch bar, turn BOTH FDs off, which will (or should...) change the A/THR into SPD mode.

We learned that lesson over 25 years ago...

:ugh::ugh::ugh:

What a :mad: of an approach & go-around.

It seems that AF ( with the longest history of any A320 operator if we include the ex Air Inter crews) & this particular Capt (who had "only" 9800hrs on type ) still haven't grasped the modes/logic/idiosyncrocities of the Bus.

Am I alone in finding that concept slightly disturbing, particularly whenever I am forced to clamber in the back of one to (hopefully) be conveyed from home to base.

Quote from captplaystation (my emphasis):

It seems that AF ( with the longest history of any A320 operator if we include the ex Air Inter crews) & this particular Capt (who had "only" 9800hrs on type ) still haven't grasped the modes/logic/idiosyncrocities of the Bus.

This mistake rapidly became a classic no-no by the latter part of 1988 in my airline. The best spin one might be able put on this incident is that the low-hours-on-type co-pilot/PF forgot his recent training, and the captain was so distracted (for reasons unknown) that he failed to notice the pitch bar disappearing downwards, and failed to monitor the speed. (In OP DES mode, with A/THR consequently in IDLE mode, only the elevator can control the speed.)

I'm a little surprised that the speed got down to Valpha-floor, however. After the Bangalore accident, the FMGS logic was modified to switch automatically from OP DES mode to VS mode when the IAS fell much below VLS. (can't remember the figure right now). When the FMGS switches to VS mode, the A/THR mode changes from IDLE to SPD.

You got one thing badly wrong, though. The joint launch-customers for the A320 were AF and BR (British Caledonian... remember?). Air Inter was third in the line. BR became BA on 1/4/88, the day our first A320 (G-BUSB) was delivered. BA's accident-free operation (we bought 10) may have got less publicity than the others. See the Habsheim thread?

AF
 

AF and Airbus are a lethal mix ideologically and technologically.
In fact, if there had been a plebiscite by AF Unions, they would have voted to be an all-Boeing fleet hands-down.

Air France appalling CRM again......
 

Shaking my head at how the conduct of a crew on a national flag carrier can result in this.......

Report: Air France A320 at Tel Aviv on Apr 3rd 2012, approach to stall on turning final results in Alpha Floor and flaps overspeed

Hmmmmm

Puts paid to the notion that Koreans, for unique cultural reasons, can't fly.

Am I corect in believing that this all happened in Normal Law?
Good. Go Around on a bad approach, come back, get her back on the ground.

Why is the PM applying control inputs contrary to the PF's inputs? Why is the PM applying control inputs at all? Do they not state 'I/you have control'? Forgotten some of the basics and past lessons? Similar stuff was going on in the stall non-recovery of AF447.

Re Puts Paid (GF):

What notion; that they can't fly?

Boofhead

Spend some time over at the Asiana thread. Lots of comments that Korean (French?) culture makes them poor at CRM, ability to handle large aircraft.

Pull up into a stall or push into a recovery... Airbus saves the day.

A First Officer with 27,500 hours? Something odd there.

Maybe he's an 80,000+