explain the "auto throttle" to me/us
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Originally Posted by gums
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).
Thread Starter
@ 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.
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.
Originally Posted by Dave Wilson
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...
Bottums Up
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.
Originally Posted by Galaxy Flyer
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.
PS: Wouldn't "Thrust" indicate speed was being controlled by thrust, not pitch, as appears to the case in your example?
Originally Posted by Clarrie
From the perspective of the 717 I can't see why it seems so hard.
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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.
. 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.
Originally Posted by Dave Wilson
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.
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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?
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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.
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.
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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.
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.
Thread Starter
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.
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?
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?
Originally Posted by GF
Yes, THRUST mode is speed on pitch, power is either idle or CLB, depending vertical direction.
Originally Posted by Dave
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?
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.
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.
What struck me was in the event of a single-engine approach it was prohibited (not just discouraged) to use the A/T system. (Don't know if same applies to the 717.)
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Why you'd want to slam on the power/go a lot faster to avoid another aeroplane is also a bit of a mystery.
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.
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.