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The Tristar automated descent control system

Posted: Thu Aug 22, 2019 4:30 pm
by cargil48
Hi, everyone

Going back to the times when the new technologies were launched which today are standard, I found out that the Lockheed L-1011 Tristar had an "automated descent control system". Searching all over the net, I cannot find a description of what exactly that feature is about. Just out of curiosity for technical features in aviation, cfan someone enlighten me on this subject? Thaks in advance.

Re: The Tristar automated descent control system

Posted: Thu Aug 22, 2019 5:03 pm
by BravoOne
I flew it for about four years and never heard of such a thing.

Re: The Tristar automated descent control system

Posted: Thu Aug 22, 2019 5:06 pm
by BoeingGuy
I think he’s probably talking about DLC used during approach.

Re: The Tristar automated descent control system

Posted: Thu Aug 22, 2019 5:57 pm
by extender
BoeingGuy wrote:
I think he’s probably talking about DLC used during approach.


+1

Link

Re: The Tristar automated descent control system

Posted: Thu Aug 22, 2019 6:21 pm
by BravoOne
By coincidence I just had coffee with a couple of guys, one of which was a retired Lockheed production flight test pilot. He could not recall anything as described. Suspect as others have said you are looking at the DLC, aka direct lift control.

Re: The Tristar automated descent control system

Posted: Thu Aug 22, 2019 11:28 pm
by 426Shadow
Sounds like you might have recently purchased the Captainsim L1011.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 1:03 am
by GalaxyFlyer
When flaps went to 33*, the spoilers went to a preset extension position. On the glide slope if a bit high, a light forward pressure on the yoke, instead pitching the nose down, the spoilers went up decreasing lift and the plane “sank” back to the glide slope. And, just the opposite when low, the spoilers would retract, increase lift and the plane without a pitch change go back to the slope.

Worked great, when it worked, until the flare. If checked a bit float with the slightest forward pressure, the spoilers went up, the plane landed somewhere between firm and, “the engineer can greet the passengers”.


GF

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 2:26 am
by BravoOne
I do not recall the L1011 as having any bad landing characteristics as you describe. Sure wasn't any exceptional skills on my part so I'll have to call you on that one.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 2:37 am
by fr8mech
BravoOne wrote:
I do not recall the L1011 as having any bad landing characteristics as you describe. Sure wasn't any exceptional skills on my part so I'll have to call you on that one.


I've flown in an L1011 just once, happened to be in one of the jumpseats with Delta back in '88 - ATL/LGA.

We landed long. We landed hard. Later that night, I was assigned to replace the 3 wheels that had thermaled.

So, 100% of the L1011 landings I've endured, have sucked.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 2:42 am
by BravoOne
Sorry to hear that. I would suggest your range of expertise is pretty small regarding the handling qualities of the L1011. Without knowing the exact circumstances surrounding the approach and landing it would be hard to comment other "Long and hard" conjures all sorts of thoughts:)

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 4:26 am
by fr8mech
BravoOne wrote:
I would suggest your range of expertise is pretty small regarding the handling qualities of the L1011.


And, I've indicated no different.

But, I know a bad landing when I feel one, even at the tender age of 20. The fact that I remember that landing, should be an indicator of the imprint the landing made. True, it was my first jumpseat flight, but the only thing I remember about that flight was the landing, and it was a thing of beauty.

BravoOne wrote:
Without knowing the exact circumstances surrounding the approach and landing


Dodging storms, with a wet runway. I do know we landed on 31 because we pulled right off and entered the DAL terminal area.

BravoOne wrote:
other "Long and hard" conjures all sorts of thoughts


Yeah, I toyed with writing "a long and hard landing", followed by "blown tires", but I demurred, and made 2 separate sentences.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 4:58 am
by fr8mech
Runway 13, not 31.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 11:04 am
by cargil48
BravoOne wrote:
I flew it for about four years and never heard of such a thing.


«The aircraft has a sophisticated autoland capability, an automated descent control system, (...)»
http://www.concordespeakers.com/12-othe ... ed-tristar

Maybe you're correct, maybe this feature is another way of describing the DLC... Hence my specific question about this matter.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 11:10 am
by cargil48
And I know how DLC works, I've read enough stuff about it. Also about what NOT TO DO, when on the flare. It seems to me this technique is fine for the glideslope approach phase but required a lot of training of the crews. Exactly for not doing hard landings.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 11:17 am
by cargil48
fr8mech wrote:
BravoOne wrote:
Without knowing the exact circumstances surrounding the approach and landing


Dodging storms, with a wet runway. I do know we landed on 31 because we pulled right off and entered the DAL terminal area.


If landing during rough weather conditions a "hard landing" is normal. I recall a captain saying to his F/O "tie her down!" just prior to touch down, once, in one of many rides in the jumpseats...

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 11:29 am
by cargil48
What I'd like to add here is:
a) I don't have (never had...) a Flight sim. Rode too often in the cockpits of different airplanes to know more or less how things work to make a plane fly...
b) My main interest in all this stuff is to get more knowledge about how automated systems became available in commercial aviation, the Tristar being really "the champion" in this area... And why this interest about this subject? You got it, MCAS and the associated troubles...
How did the industry became able in the 70s to get complex automation into airplanes (where as we all know there is the need of many, many systems and sensors to feed them with info) and now - 2019, guys!!...) 400+ 737MAX are sitting like lame ducks all over the airports of the world... Sounds crazy, doesn't it?
But this is another story and no, my aim is NOT to do "Boeing bashing"... My aim is trying to understand how back in the 70s they were able to make Tristars perform CAT IIIc autolands and glidepath holding systems and - as far as I'm concerned - back then I never heard or read about a "faulty indication to the flight computer system" leading to a crash (or two, to be more precise).

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 11:37 am
by cargil48
extender wrote:
BoeingGuy wrote:
I think he’s probably talking about DLC used during approach.


+1

Link


Thanks for the link, "extender"! Very interesting for a technology buff like me!...

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 3:41 pm
by Zeke2517
I’ve always wondered, if DLC engaged automatically and caused the yoke to move the spoilers while the plane maintains a fixed pitch, how did the aircraft know what pitch to maintain?

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 4:16 pm
by cargil48
Zeke2517 wrote:
I’ve always wondered, if DLC engaged automatically and caused the yoke to move the spoilers while the plane maintains a fixed pitch, how did the aircraft know what pitch to maintain?


Taking in account of what I've read so far, it responds to slight manual inputs to the yoke. But, I repeat: Slight inputs!... Say, you're seating in nr. 1 seat, flaps 30 and maintaining a glidepath with a determined power setting. Now you see at the VSI that you're a bit too high. You pull the yoke just a little bit forward and the spoilers augment their deflection a bit. When you see at the Attitude Indicator that you're back on track, you pull the yoke slightly back again into neutral and the spoilers react accordingly. That's why they call it "automated"... but responding to manual inputs. As I've read, this is (or was...) to avoid the PIC to handle the throttles to maintain the correct descend path, "to give the pax a smoother ride"... I say here BS!... It might yes have been to avoid a "see-saw-type of descent" on the part of lesser able pilots... PS: Like, many, many years later, the Turkish B-737 accident at AMS, when they landed in the middle of a potato field... or was it tulips?... :)

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 4:51 pm
by BravoOne
I think most pilots who have actually flown the L1011 will agree that it is a very nice stable platform and much better than either the DC10, MD11, and even the almighty 747. Don't know what the background of the OP is but I suspect he has not flown any of these aircraft, so the BS comment remains dubious at best.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 5:32 pm
by cargil48
BravoOne wrote:
I think most pilots who have actually flown the L1011 will agree that it is a very nice stable platform and much better than either the DC10, MD11, and even the almighty 747. Don't know what the background of the OP is but I suspect he has not flown any of these aircraft, so the BS comment remains dubious at best.


It sure is a very stable platform, who said the opposite? Where? When? The B-737 is also one of the most stable platforms ever produced and... The Airbus A340 as well, and one fell flat into the ocean some years ago... Can't you separate the hardware from some kind of "software"?? It is for the "lesser equipped software programs" so to speak that all the "automation processes" like the one we are talking about here, or even more the MCAS, have been developed... and put into very stable airplanes, no doubt about that!... Don't you get the point?

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 6:11 pm
by BravoOne
Wow, please let know where your area of expertise lies when rambble on with these internet armchair BS comments. It's hard to know where to start. Yes, I'm failing to get your point?

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 6:25 pm
by Zeke2517
cargil48 wrote:
Zeke2517 wrote:
I’ve always wondered, if DLC engaged automatically and caused the yoke to move the spoilers while the plane maintains a fixed pitch, how did the aircraft know what pitch to maintain?


Taking in account of what I've read so far, it responds to slight manual inputs to the yoke. But, I repeat: Slight inputs!... Say, you're seating in nr. 1 seat, flaps 30 and maintaining a glidepath with a determined power setting. Now you see at the VSI that you're a bit too high. You pull the yoke just a little bit forward and the spoilers augment their deflection a bit. When you see at the Attitude Indicator that you're back on track, you pull the yoke slightly back again into neutral and the spoilers react accordingly. That's why they call it "automated"... but responding to manual inputs. As I've read, this is (or was...) to avoid the PIC to handle the throttles to maintain the correct descend path, "to give the pax a smoother ride"... I say here BS!... It might yes have been to avoid a "see-saw-type of descent" on the part of lesser able pilots... PS: Like, many, many years later, the Turkish B-737 accident at AMS, when they landed in the middle of a potato field... or was it tulips?... :)


Yeah that’s not really what I was asking.

Anyone else?

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 6:45 pm
by cargil48
Zeke2517 wrote:
Zeke2517 wrote:
I’ve always wondered, if DLC engaged automatically and caused the yoke to move the spoilers while the plane maintains a fixed pitch,(...)


(...)

Yeah that’s not really what I was asking.

Anyone else?


I tried to show you that your assumption is not correct.
if DLC engaged automatically and caused the yoke to move the spoilers while the plane maintains a fixed pitch


It isn't the DLC which causes the yoke to move the spoilers, it's as I explained the PIC when he senses the glidepath is being overridden or underpassed.

Or, if you're referring to the "autoland system" you have to say so. That's another story and how that system gets the inputs it needs I don't know, but I guess it's through the beam emitted by the localizer.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 9:53 pm
by BoeingGuy
cargil48 wrote:
Zeke2517 wrote:
I’ve always wondered, if DLC engaged automatically and caused the yoke to move the spoilers while the plane maintains a fixed pitch, how did the aircraft know what pitch to maintain?


Taking in account of what I've read so far, it responds to slight manual inputs to the yoke. But, I repeat: Slight inputs!... Say, you're seating in nr. 1 seat, flaps 30 and maintaining a glidepath with a determined power setting. Now you see at the VSI that you're a bit too high. You pull the yoke just a little bit forward and the spoilers augment their deflection a bit. When you see at the Attitude Indicator that you're back on track, you pull the yoke slightly back again into neutral and the spoilers react accordingly. That's why they call it "automated"... but responding to manual inputs. As I've read, this is (or was...) to avoid the PIC to handle the throttles to maintain the correct descend path, "to give the pax a smoother ride"... I say here BS!... It might yes have been to avoid a "see-saw-type of descent" on the part of lesser able pilots... PS: Like, many, many years later, the Turkish B-737 accident at AMS, when they landed in the middle of a potato field... or was it tulips?... :)


Your Turkish Airways comment has absolutely nothing to do with the topic being discussed.

The Autothrottle had a malfunction and reduced to idle at about 1000 feet (IIRC). The crew just sat there and watched the airplane fall out of the sky rather than being pilots and actually flying the airplane and taking over manual thrust control.

By the way, the 737 Max has DLC also as a backup to land safely if there was a flight controls jam. I’m guessing that is a little known fact.

Re: The Tristar automated descent control system

Posted: Fri Aug 23, 2019 10:35 pm
by BravoOne
cargil48 wrote:
Zeke2517 wrote:
Zeke2517 wrote:
I’ve always wondered, if DLC engaged automatically and caused the yoke to move the spoilers while the plane maintains a fixed pitch,(...)


(...)

Yeah that’s not really what I was asking.

Anyone else?


I tried to show you that your assumption is not correct.
if DLC engaged automatically and caused the yoke to move the spoilers while the plane maintains a fixed pitch


It isn't the DLC which causes the yoke to move the spoilers, it's as I explained the PIC when he senses the glidepath is being overridden or underpassed.

Or, if you're referring to the "autoland system" you have to say so. That's another story and how that system gets the inputs it needs I don't know, but I guess it's through the beam emitted by the localizer.



Wrong again!

Re: The Tristar automated descent control system

Posted: Sat Aug 24, 2019 5:43 am
by SAAFNAV
So, OP, let me get this straight:

You come on here to ask questions, then you start teaching some actual pilots, some of them who also flew the L-1011, about how it works.
Your comments actually shows that you have no idea how the systems work, or are integrated to create an autoland system (hint: you need more than a localizer beam for autoland, and also some airborne emitters).


Also, try to use less ellipses and more paragraphs, then we would also have a better idea of what you are trying to say.

Re: The Tristar automated descent control system

Posted: Sat Aug 24, 2019 7:24 am
by 747classic
DLC's purpose is to allow vertical corrections to the glide slope to be accomplished without use of pitch control. When the flaps are lowered beyond 30 degrees the four inboard spoilers on each wing assume a new null point. Excursion above or below the glide slope will cause the spoilers to extend or retract bring the aircraft back to the glide slope. This is accomplish automatically through the Flight Controls Electronics Computer (FCES) and works in both autopilot and manual modes.

See the discussion in an old thread about DLC : viewtopic.php?t=737027

And look for the video (beginning at 3.54 min) at reply 20 (DL_ Mech) : https://www.youtube.com/watch?v=Vf2nFYHKGuU

Re: The Tristar automated descent control system

Posted: Sat Aug 24, 2019 8:50 am
by cargil48
Thanks, 747classic, that is a positive entry on your part.With people like you one can have a debate about very intricate technical subjects.Also "Boeing guy" had a very positive reply to a point I commented here. Thanks for that.

But before terminating my questions and comments let me say only one thing to those feeling the need "to get first something straight": Zeke2517's question:

I’ve always wondered, if DLC engaged automatically and caused the yoke to move the spoilers while the plane maintains a fixed pitch, how did the aircraft know what pitch to maintain?


is still not answered, why? SAANAV, maybe you could help him out with your expertise. That would be a positive way to act, right?

Re: The Tristar automated descent control system

Posted: Sat Aug 24, 2019 9:07 am
by zeke
cargil48 wrote:
BravoOne wrote:
I flew it for about four years and never heard of such a thing.


«The aircraft has a sophisticated autoland capability, an automated descent control system, (...)»
http://www.concordespeakers.com/12-othe ... ed-tristar

Maybe you're correct, maybe this feature is another way of describing the DLC... Hence my specific question about this matter.


I think in the context of that sentence they are referring to VNAV, it was the first airliner I think to have VNAV and some other pretty special auto-land capabilities.

Re: The Tristar automated descent control system

Posted: Sat Aug 24, 2019 11:07 am
by 747classic
I found this very interesting link : https://www.airlinereporter.com/2015/09 ... 1-tristar/

Also the reply's of several crews that actually have flown the Tristar at the bottom of this article are interesting, especially those regarding the DLC and the autoland capabilities.

Note :
I actually witnessed a practice cat IIIb autoland * , with. DLC at a positioning flight in a Gulf Air L1011 Tristar at the flightdeck (observer's seat) in the eighties.
I remember I was impressed by the the very stable approach, with no movement at all of both control yoke and auto throttle (until the flare), compared to " our" 747 classic series with only cat IIIa autoland capability.

* = We were positioning in uniform, so I asked the captain for a cockpit seat. I was aware of the Tristar's "lift dumping glideslope feature" . After a nice conversation about the differences between the autoland performance of the 747 and the L1011, the captain offered to perform a practice autoland at DXB to demonstrate the L1011 autoland system.

Re: The Tristar automated descent control system

Posted: Sat Aug 24, 2019 1:31 pm
by BravoOne
zeke wrote:
cargil48 wrote:
BravoOne wrote:
I flew it for about four years and never heard of such a thing.


«The aircraft has a sophisticated autoland capability, an automated descent control system, (...)»
http://www.concordespeakers.com/12-othe ... ed-tristar

Maybe you're correct, maybe this feature is another way of describing the DLC... Hence my specific question about this matter.


I think in the context of that sentence they are referring to VNAV, it was the first airliner I think to have VNAV and some other pretty special auto-land capabilities.


Perhaps, but I suspect that is not the point of reference. Some of the L1011's that we operated had poor mans FMS installed that played through the Carosel IV. You could program it to cross a fix at at defined altitude and in addition I think you could string more than the 9 wpts that were limiting on the Carousel system. It was awkward to use so most of the pilots did not use this feature. The only other airline that I saw with this FMS was Saudia, but there may have been others. The -250 and -500 did not use this system but rather simply used a triple Carousel set up with no VNAV capability to speak of.

Re: The Tristar automated descent control system

Posted: Sun Aug 25, 2019 6:20 am
by 747classic
BravoOne wrote:
zeke wrote:

I think in the context of that sentence they are referring to VNAV, it was the first airliner I think to have VNAV and some other pretty special auto-land capabilities.


Perhaps, but I suspect that is not the point of reference. Some of the L1011's that we operated had poor mans FMS installed that played through the Carosel IV. You could program it to cross a fix at at defined altitude and in addition I think you could string more than the 9 wpts that were limiting on the Carousel system. It was awkward to use so most of the pilots did not use this feature. The only other airline that I saw with this FMS was Saudia, but there may have been others. The -250 and -500 did not use this system but rather simply used a triple Carousel set up with no VNAV capability to speak of.


The first L1011's were delivered with Carousel IV INS systems, indeed with a max of 9 waypoints. At that time this was the most sofisticated navigation possible.(also installed at the 747 classics)
Later L1011's were delivered/upgraded with a Performance Managment System (PMS) , as an option FMS could also be included.
See : https://www.tristar500.net/library/technicalprofile.pdf
and look for DLC (page 12/18) and PMS (page 13/18)

Re: The Tristar automated descent control system

Posted: Sun Aug 25, 2019 12:04 pm
by slcguy
Think there is a lot of confusion here based on the original post's terminology. Yes the L-1011 had the most advanced autopilot/autothrottle and autoland system of it's time but not much different and led to what is found today on most modern planes. The DLC (direct lift control) using the spoilers was totally different function. When small altitude/glideslope corrections were needed on approach either manually by the pilots using the yoke or commanded by the autopilot the small movement of the spoilers would adjust the sink rate without the pitch angle and speed of the aircraft changing. This made for a very stable pitch angle and smooth ride on approach. In cases where more than small corrections were needed the elevators would move normally.

Re: The Tristar automated descent control system

Posted: Sun Aug 25, 2019 1:34 pm
by cargil48
Thank you, gentlemen, you've put the debate of this issue on the correct track... and given precious information for all those wishing to do the same as me: To go back to the first systems of automation in commercial airplanes. I think this is fascinating stuff regardless of one being or having been a pilot or not.

Re: The Tristar automated descent control system

Posted: Mon Aug 26, 2019 6:50 pm
by WPvsMW
Several DL Tristar captains explained the DLC to me, when they would hang out in the galley mid-flight (HNL/ATL) during breaks (pre-B764), as a DOD-driven feature for cargo ops (Tristar's design as a "better" military transport vs. competitors).

Re: The Tristar automated descent control system

Posted: Mon Aug 26, 2019 8:41 pm
by BravoOne
WPvsMW wrote:
Several DL Tristar captains explained the DLC to me, when they would hang out in the galley mid-flight (HNL/ATL) during breaks (pre-B764), as a DOD-driven feature for cargo ops (Tristar's design as a "better" military transport vs. competitors).



That makes absolutely no sense at all?

Re: The Tristar automated descent control system

Posted: Mon Aug 26, 2019 9:37 pm
by WPvsMW
B1, I'm repeating what the 4-bars said, .... could be apocryphal within DL... 30 years ago.

Re: The Tristar automated descent control system

Posted: Mon Aug 26, 2019 10:32 pm
by GalaxyFlyer
I’d agree on “no sense at all”. Yes, B1, the EAL guy’s might have been blaming the DLC for a bad landing and gullible jumpseater bought it, hook, line and you know the rest

Re: The Tristar automated descent control system

Posted: Mon Aug 26, 2019 10:33 pm
by BravoOne
WPvsMW wrote:
B1, I'm repeating what the 4-bars said, .... could be apocryphal within DL... 30 years ago.


Yea, I know what you mean as I was there 30 years ago as well:)

Re: The Tristar automated descent control system

Posted: Fri Aug 30, 2019 1:30 pm
by cargil48
slcguy wrote:
Think there is a lot of confusion here based on the original post's terminology. Yes the L-1011 had the most advanced autopilot/autothrottle and autoland system of it's time but not much different and led to what is found today on most modern planes. The DLC (direct lift control) using the spoilers was totally different function. When small altitude/glideslope corrections were needed on approach either manually by the pilots using the yoke or commanded by the autopilot the small movement of the spoilers would adjust the sink rate without the pitch angle and speed of the aircraft changing. This made for a very stable pitch angle and smooth ride on approach. In cases where more than small corrections were needed the elevators would move normally.


slcguy, thank you for that most comprehensible explanation of DLC. My question, however, was slightly different... Knowing from the first moment on what DLC meant on the Tristar, I questioned that other term for which I couldn't find any explanation ("automated descent control system")... That is what confused me... If those who wrote that confusing terminology meant simply "autoland", why didn't they write so?? Because DLC is certainly nothing "automated" but - as you all have described - a spoiler assisted glidepath holding device.

Re: The Tristar automated descent control system

Posted: Sat Aug 31, 2019 6:00 am
by cc2314
Have had a stint in the jump seat of euro Atlantic last l1011, we operated out of Dublin mid 00s.. We had a 763er at the time and many of the flight crew were flying both types.
The l10 had smooth landings, one thing to note the nose wheel often came to ground near the completion of the landing run.
Have had many horrendous hard landings on the 767,has made me wonder is it a bad pilot issue or bad aircraft design.

Iirc the captains name on the l10 was Carlos Pirez, from euroatlantic.