explain the "auto throttle" to me/us
Thread Starter
Thanks Scud.
Not what I wanted to hear, but if the heavy folks can live with such an implentation ( or die with 200 SLF in the back), then seems their choice( the SLF don't vote).
I can understand some basic profile settings, like climb for optimum rate of climb or range when cruising, and descent to a specified atltitude, tho I don't like that one, and the Asiana crew witnessed that sub-mode of Otto and throttle otto).
My only experience with the climb and descent otto, held the speed or mach, and I set the throttle to whatever I wanted or needed.
I can also understand the jet adjusting the power once level to get the best cruise mach and such. Ditto for a climb profile, but don't know why otto would adjust the throttle(s) as the crew could just set the power to the basic setting from the manaul.
But seems to me that there are still a plethora of modes and sub-modes that are connected with the autopilot modes, and it gets confusing.
If the policy is to fly the USAF technique of point the jet and use throttle for speed, regardless of the optimum AoA for an approach, then I understand that. But the last thing I wanted was a system that was hard to understand depending upon a host of other systems that were supposed to "help" you.
Even if the whole profile was flown by HAL, then the faux pilots would have to monitor system operation and detect a problem or whatever. Why not just fly the jet yourself and take pride in nailing the mach for climb and cruise and setting power for descent to reach the initial approach fix at the right altitude and.....
Not what I wanted to hear, but if the heavy folks can live with such an implentation ( or die with 200 SLF in the back), then seems their choice( the SLF don't vote).
I can understand some basic profile settings, like climb for optimum rate of climb or range when cruising, and descent to a specified atltitude, tho I don't like that one, and the Asiana crew witnessed that sub-mode of Otto and throttle otto).
My only experience with the climb and descent otto, held the speed or mach, and I set the throttle to whatever I wanted or needed.
I can also understand the jet adjusting the power once level to get the best cruise mach and such. Ditto for a climb profile, but don't know why otto would adjust the throttle(s) as the crew could just set the power to the basic setting from the manaul.
But seems to me that there are still a plethora of modes and sub-modes that are connected with the autopilot modes, and it gets confusing.
If the policy is to fly the USAF technique of point the jet and use throttle for speed, regardless of the optimum AoA for an approach, then I understand that. But the last thing I wanted was a system that was hard to understand depending upon a host of other systems that were supposed to "help" you.
Even if the whole profile was flown by HAL, then the faux pilots would have to monitor system operation and detect a problem or whatever. Why not just fly the jet yourself and take pride in nailing the mach for climb and cruise and setting power for descent to reach the initial approach fix at the right altitude and.....
Thread Starter
Sorry Flyboy, I mean "implementation", how a concept is implemented.
Start with the operational requirement, get some ideas from the players, refine the requirements, get some proposals, then decide to go with brand "x" or brand "y". Basic systens engineering and procurement stuff. Gone are the days that a company can roll out a plane and get some customers.
Bus and Boing seem to figure out what the "need" is, and propose something. If the major carriers don't seem interested, then they refine and improve what is already flying.
Start with the operational requirement, get some ideas from the players, refine the requirements, get some proposals, then decide to go with brand "x" or brand "y". Basic systens engineering and procurement stuff. Gone are the days that a company can roll out a plane and get some customers.
Bus and Boing seem to figure out what the "need" is, and propose something. If the major carriers don't seem interested, then they refine and improve what is already flying.
My only experience with the climb and descent otto, held the speed or mach, and I set the throttle to whatever I wanted or needed.
but don't know why otto would adjust the throttle(s) as the crew could just set the power to the basic setting from the manaul.
If the policy is to fly the USAF technique of point the jet and use throttle for speed, regardless of the optimum AoA for an approach
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Auto throttles are very simple things and they all work pretty much the same way. Speed on thrust or speed on elevator depending on the selected vertical mode. The will also have a hold or clamp mode if they are used for take off, this is to prevent the AT system buggering up the take off and a retard mode that is triggered at some radio height over the threshold.
Nothing to it really.
Nothing to it really.
Thread Starter
C'mon, Bloggs
The optimum AoA for approach, climb, range etc. is what it is. The speed is a result of your configuration at the AoA ( slotted flaps, leading edge devices, etc factored in).
The jet stalls at "x" AoA, and speed could be above or below the manual's number - think accelerated stall and such.
I did not appreciate the concept of the AoA "indexer" lights on the gunsight/HUD until flying the SLUF. Then, we had the actual AoA bracket next to our flight path marker in the HUD. Sheesh, how could it have been easier, with no flight directors or auto-anything? Our AoA was the real deal, and compensated for gross weight without us doing anything. Some configuration factors came into play, but the basic AoA didn't change much - figure a degree or so AoA.
We usually set a power of 95% or so for our wingies when climbing. Then we climbed at a mach or a generic speed while trimming for such. Sheesh. Easy. Upon level, got to the best mach and used whatever power we had to, duhhhh? Why is that so hard?
It would seem to me that basic throttle settings for climb, cruise and descent would be easy to know. For approach, if you need otto to help, then fine. but quit connecting the throttle to the AP modes. If you want to "point" and use throttle for speed, your choice.
The optimum AoA for approach, climb, range etc. is what it is. The speed is a result of your configuration at the AoA ( slotted flaps, leading edge devices, etc factored in).
The jet stalls at "x" AoA, and speed could be above or below the manual's number - think accelerated stall and such.
I did not appreciate the concept of the AoA "indexer" lights on the gunsight/HUD until flying the SLUF. Then, we had the actual AoA bracket next to our flight path marker in the HUD. Sheesh, how could it have been easier, with no flight directors or auto-anything? Our AoA was the real deal, and compensated for gross weight without us doing anything. Some configuration factors came into play, but the basic AoA didn't change much - figure a degree or so AoA.
We usually set a power of 95% or so for our wingies when climbing. Then we climbed at a mach or a generic speed while trimming for such. Sheesh. Easy. Upon level, got to the best mach and used whatever power we had to, duhhhh? Why is that so hard?
It would seem to me that basic throttle settings for climb, cruise and descent would be easy to know. For approach, if you need otto to help, then fine. but quit connecting the throttle to the AP modes. If you want to "point" and use throttle for speed, your choice.
The advantage to modern auto flight systems is just like the cruise control in your car is that can operate very efficiently making very small corrections. The basic operating is very simple, but really understanding them is much more difficult. As shown by the Koreans --they could use but didn't really understand about the hold mode. The other problem is that you need to actually know how to fly when things don't go perfectly. Apparently the Koreans couldn't do that either. I flew the A 320 for a long time and always told new guys that the magistrate stuff works great so use it, but don't ever completely trust it. It is kind of like flying with a student--never let it put in a position that you can't recover from. Another problem the Koreans had and something they don't teach you in training.
The optimum AoA for approach, climb, range etc. is what it is. The speed is a result of your configuration at the AoA ( slotted flaps, leading edge devices, etc factored in).
The jet stalls at "x" AoA, and speed could be above or below the manual's number - think accelerated stall and such.
The jet stalls at "x" AoA, and speed could be above or below the manual's number - think accelerated stall and such.
Airliners generally don't do accelerated stalls
so the stalling speed is always the same for a particular configuration and in any case is calculated by the FMS (taking into account all sorts of things like C of G) and is displayed on the ASI by way of Vref, being the stall plus 30%.
We usually set a power of 95% or so for our wingies when climbing. Then we climbed at a mach or a generic speed while trimming for such. Sheesh. Easy. Upon level, got to the best mach and used whatever power we had to, duhhhh? Why is that so hard?
For approach, if you need otto to help, then fine. but quit connecting the throttle to the AP modes. If you want to "point" and use throttle for speed, your choice.
Some types, like mine, recommend using the autothrottle all the time, AP in or out. And it does a far better job than I ever could. "pointing and using the throttle for speed" is simply flying without the AP or the autothrottle. Problem?
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From his posts gums is addressing two very different things in my opinion. One is the use of automatics including autothrust and the other is basic airmanship.
Using automatics has improved safety considerably, however as we now see for a couple years, despite a record breaking low accident count, is the fact that pilots still need to be pilots and need basic airmanship. That said automatic flight systems are tools. Nothing more, nothing less. A professional pilot needs to know his automatics inside out as well as he needs to be able to fly manually if the need arises and of course has the ability to monitor what the aircraft and its system are doing. The latter one is actually the hardest task and human beings are not very good at monitoring,
Autothrust is very good at what it does, and over the long and incredibly boring hours of commercial flight, it is much better than any human being could ever be. However as any system it has its limitations, design criteria which it follows and different modes that work according to what state of flight they were designed to be used in. Using Level Change, or Flight Level Change, for a visual approach seems to be a rather odd use of autothrust mode in my opinion, certainly no mode i would ever use in the tiny boeing, however as i'm not rated on the huge twin i can't possibly comment if it is a normal use of AT mode there. In my outfit we would usually fly a visual in manual flight with the AT in arm (which provides low speed protection) and knowing that we have to set thrust manually.
Using automatics has improved safety considerably, however as we now see for a couple years, despite a record breaking low accident count, is the fact that pilots still need to be pilots and need basic airmanship. That said automatic flight systems are tools. Nothing more, nothing less. A professional pilot needs to know his automatics inside out as well as he needs to be able to fly manually if the need arises and of course has the ability to monitor what the aircraft and its system are doing. The latter one is actually the hardest task and human beings are not very good at monitoring,
Autothrust is very good at what it does, and over the long and incredibly boring hours of commercial flight, it is much better than any human being could ever be. However as any system it has its limitations, design criteria which it follows and different modes that work according to what state of flight they were designed to be used in. Using Level Change, or Flight Level Change, for a visual approach seems to be a rather odd use of autothrust mode in my opinion, certainly no mode i would ever use in the tiny boeing, however as i'm not rated on the huge twin i can't possibly comment if it is a normal use of AT mode there. In my outfit we would usually fly a visual in manual flight with the AT in arm (which provides low speed protection) and knowing that we have to set thrust manually.
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If the speed gets too slow because Bloggs continues to pull/hold the nose up, any decent AT system will spring to life regardless of previous pilot selections and save the day.
Apparently the 777 doesn't do this.
It will in any mode EXCEPT "Hold"- INCLUDING disengaged!
Apparently the 777 doesn't do this.
It will in any mode EXCEPT "Hold"- INCLUDING disengaged!
Itīs not true ...you seem to mix ARMED and DIDENGAGED/DISCONNECT functions
Even in HOLD mode , A/T will react , I agree lately , but it will react provided A/T arm switch on the MCP is armed which is always the case .
Precisely, when speed is approaching middle part of speed amber scale , your autothrottle becomes "awake" , Speed mode engages et your auto throttle is keeping speed on top of speed amber scale which is MMS minimum manoeuvring speed.
More info on PLI activation, caution air speed low and trim inihibits are available by your nearest retailer ..
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Originally Posted by Capt Bloggs
Gums, you've lost me. For any configuration, there is only one speed that will give you a particular AoA. That is why Vref to the knot is used by airliners. Somebody decided many moons ago that speed would be a better "target" to use.
Airliners generally don't do accelerated stalls so the stalling speed is always the same for a particular configuration and in any case is calculated by theFMS (taking into account allsortsof thingslikeC of G)and is displayed on the ASI by way of Vref, being the stall plus 30%.
Airliners generally don't do accelerated stalls so the stalling speed is always the same for a particular configuration and in any case is calculated by theFMS (taking into account allsortsof thingslikeC of G)and is displayed on the ASI by way of Vref, being the stall plus 30%.
See the PRANDTL basic curve : all the points are mesured at the same speed, but different AoA.
Speed is a bad indicator of stall. Only AoA is true
gums is true.
Last edited by roulishollandais; 14th Dec 2013 at 19:21.
I can't understand the aversion to using AoA to control flight in the take-off, approach and landing phases in heavies, airlines, FAA-world. I used it in the T-38, the Citation (same indexer display) and the C-5 (no indexer, but 7 units for approach, from configuring to landing). Not very useful in cruise, I'll admit. An AoA indication was installed on our Bombardier planes, but NO flight-verified recommended indications for any operations. We were told to "let us know how it works and what approach indications are, the FAA won't certify it".
The wing flies on AoA, not airspeed.
The wing flies on AoA, not airspeed.
When 4D gets here, I'm going to shooting range. 
. I didn't say airspeed Could be replaced, just that AoA can be better in some regimes. And, not subject to incorrect weight calculations, for example. A thousand hours in the A-10 and hardly ever used that Tweet airspeed indicator on approach.
. I didn't say airspeed Could be replaced, just that AoA can be better in some regimes. And, not subject to incorrect weight calculations, for example. A thousand hours in the A-10 and hardly ever used that Tweet airspeed indicator on approach.
A thousand hours in the A-10 and hardly ever used that Tweet airspeed indicator on approach.
I agree with you entirely about the use of AOA....and you don't have that much time before heading to the shooting range.
edit: BTW 1000 hrs in the Hog doesn't cover a lot of mileage.
Well, not much mileage, but it was several years in C-5 before I flew a leg exceeding the 10.2 hour, Yenisheir to Lajes leg in Hawg.
Back to A/T, the bizjet systems work like the Boeings--they move. The modes are Thrust (idle, if descending, CLB, if climbing) or Speed, if the vertical FD mode selected is Vert Spd or on a VNAV PATH. We have the same "FLC Trap", that is, in THRUST mode in a descent, the throttle setting commanded will be IDLE until reaching an altitude or intercepting a VNAV PATH, when they switch to SPEED and fly the commanded speed by using the throttles. IF altitude is the runway and no path is selected, no power until they see a min speed about 5 KIAS above low speed cue.
Back to A/T, the bizjet systems work like the Boeings--they move. The modes are Thrust (idle, if descending, CLB, if climbing) or Speed, if the vertical FD mode selected is Vert Spd or on a VNAV PATH. We have the same "FLC Trap", that is, in THRUST mode in a descent, the throttle setting commanded will be IDLE until reaching an altitude or intercepting a VNAV PATH, when they switch to SPEED and fly the commanded speed by using the throttles. IF altitude is the runway and no path is selected, no power until they see a min speed about 5 KIAS above low speed cue.
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I'm not a commercial pilot but having read this post with interest and being amazed at the plethora of modes that there are which all need learning, wouldn't it be a lot easier just to use manual control of the throttles? I mean, there are two of you...
Thread Starter
Thanks GF and Okie. I am getting a clearer picture from the ex-lite folks than the steeped heavy folks.
Despite my basic views of auto-throttle, I can tellya that if trying to get absolute best range in the SLUF, we would gradually pull the throttle back using the TOT ( turbine outlet temp, not EGT). The deal was as TAS wnet up, we would pull back 3 degrees of temp at a time. I forget the increase in TAS we used. But once flew from McChord to The Beach unrefueled using four bags and step climbing like the heavies seem to do for long hauls. An auto throttle rule based on mach and altitude hold would have been nice. Seems Concorde was only heavy that let altitude increase to get the best performance. Ditto for SR-71.
My main concern is if the throttle moving or not, and then the modes where the thing isn't really doing anything and the pilot thinks the sucker is working, but ain't. So think Asiana. My buddy that flew B757 and then B747 said it was easy to tell if the thing was working, as the throttle moved. 'course, he was one that kept his right hand on the throttles.
My focus upon AoA is that for a given configuration, then it is a great cross check for the calculated speed. We lites didn't have a hundred thousand pounds or more of basic weight, so a 1,000 pounds of gas was significant. After a quick WAG and rules of thuimb from the flight manual, it was comforting to see the optimum AoA in the HUD agree with the calculation. From then, you only needed to glance at speed every few seconds, and the flare was also easier looking at the AoA next to the flight path marker.
Thanks to all so far, but I still have questions about implementations and company philosophy.
Despite my basic views of auto-throttle, I can tellya that if trying to get absolute best range in the SLUF, we would gradually pull the throttle back using the TOT ( turbine outlet temp, not EGT). The deal was as TAS wnet up, we would pull back 3 degrees of temp at a time. I forget the increase in TAS we used. But once flew from McChord to The Beach unrefueled using four bags and step climbing like the heavies seem to do for long hauls. An auto throttle rule based on mach and altitude hold would have been nice. Seems Concorde was only heavy that let altitude increase to get the best performance. Ditto for SR-71.
My main concern is if the throttle moving or not, and then the modes where the thing isn't really doing anything and the pilot thinks the sucker is working, but ain't. So think Asiana. My buddy that flew B757 and then B747 said it was easy to tell if the thing was working, as the throttle moved. 'course, he was one that kept his right hand on the throttles.
My focus upon AoA is that for a given configuration, then it is a great cross check for the calculated speed. We lites didn't have a hundred thousand pounds or more of basic weight, so a 1,000 pounds of gas was significant. After a quick WAG and rules of thuimb from the flight manual, it was comforting to see the optimum AoA in the HUD agree with the calculation. From then, you only needed to glance at speed every few seconds, and the flare was also easier looking at the AoA next to the flight path marker.
Thanks to all so far, but I still have questions about implementations and company philosophy.
Short story, gums,
Landing on a beautiful day in Dallas area in a Global. Former schoolhouse IP is playing with FMS entering a " hand drawn" visual by copying the runway threshold and adding an distance/altitude final fix and cranking down the altitude selector to the field. Hand flying with A/T engaged. Because I was flying a visual pattern, I was a steeper than the defaulted 2.5 degree path and would never intercept that 2.5 degree path. As we rolled out on 2 mile final, hands on throttles, I noted speed slowing to approach expecting the throttles to start "waking" up to about 1200-1300 pph of fuel flow which they weren't doing. I clicked them off and noted THRUST in the HUD. It dawned on me what was going on. The A/T were in idle because we lacked a vertical constraint--altitude or path. Good debrief followed.
Now, I never fail to announce modes shown in the HUD or the mode annuciator.
The problem you, I and others who came out of the old generation is that we have thousands of hours of hand flying, due to the nature of the planes we flew. That experience isn't easily or, more to the point, economically, replicated today. The conversion from those planes to "magenta line" isn't always easy for types like us, but we can fallback on those previous hours of flying. Imagine never flying those hours and they take away the automatics, then add in the fact that you rarely saw throttles move.
Landing on a beautiful day in Dallas area in a Global. Former schoolhouse IP is playing with FMS entering a " hand drawn" visual by copying the runway threshold and adding an distance/altitude final fix and cranking down the altitude selector to the field. Hand flying with A/T engaged. Because I was flying a visual pattern, I was a steeper than the defaulted 2.5 degree path and would never intercept that 2.5 degree path. As we rolled out on 2 mile final, hands on throttles, I noted speed slowing to approach expecting the throttles to start "waking" up to about 1200-1300 pph of fuel flow which they weren't doing. I clicked them off and noted THRUST in the HUD. It dawned on me what was going on. The A/T were in idle because we lacked a vertical constraint--altitude or path. Good debrief followed.
Now, I never fail to announce modes shown in the HUD or the mode annuciator.
The problem you, I and others who came out of the old generation is that we have thousands of hours of hand flying, due to the nature of the planes we flew. That experience isn't easily or, more to the point, economically, replicated today. The conversion from those planes to "magenta line" isn't always easy for types like us, but we can fallback on those previous hours of flying. Imagine never flying those hours and they take away the automatics, then add in the fact that you rarely saw throttles move.
Last edited by galaxy flyer; 14th Dec 2013 at 22:58.