Thrust on during flare...Q for AIRBUS test pilots...

[nitpicker330]

That to me once again clearly indicates that Airbus want you to use A/THR to control IAS and that Pitch changes will cause changes in ROD and thus slope.
All clear indications of how they want you to FLY THEIR AIRCRAFT.

Boeing is the same.

By the way......how do you guys fly a raw data manual thrust approach using the Bird?

Surely if you were nicely on slope and 3 deg path and you want to change speed from 160 to 140 you'd keep the pitch around the same to keep the bird sitting on 3 deg whilst at the same time reducing thrust to let the damn Aircraft slow down????

Surely that's the way you'd do it???

You wouldn't go pitching up first to slow down would you???? Because let's say you did pitch up first, that will immediately put you above the GS, then you'll have to reduce thrust to increase the ROD.....messy messy messy as you wallow around the slope!!

What you in effect do is what we've said all along, thrust comes back first then you adjust pitch a small amount to keep the GS.

EXACTLY WHAT THE DAMN AUTO PILOT AUTO THRUST COMBO DO DURING COUPLED APPROACHES.....

[nitpicker330]

I gotta get a hobby outside Aviation.

However another question for them:--

What do you do when hand flying an approach using the F/D and A/THR??

I'll tell ya----

The FD pitch bar commands you to push forward or pull back to regain or maintain the GS doesn't it? ( yes it's in GS Mode ) Meanwhile the A/THR is nicely controlling the IAS ( yes it's in Speed mode.)

Hint for you-----in this case Pitch is controlling ROD and THRUST controlling the IAS..

Amazing technique isn't it.....


Now with regards to Flare----

I've been reading my copy of the Airbus instructor support notes for the A330

Here's the bit about how to FLARE the Aircraft correctly and funnily enough it DOESN'T mention adding thrust to get a secondary effect!!


Flare itself

- When reaching 100 ft RA, the pitch law is modified to be a full authority direct law with THS stopped: indeed, the normal pitch law which provides trajectory stability is not the best adapted for the flare maneuver. Additionally, pitch rate and g load feedbacks soften the A/C response to abrupt stick inputs; at 50 ft a static stability augmentation term is introduced, function of ground speed. Consequently as the speed reduces, the pilot will have to move the stick rearwards to maintain a constant path. The Flare technique is thus very conventional. Feedbacks and static stability augmentation are removed on ground. The roll is a roll rate law till the A/C is on ground. - Start the Flare at around 30 ft; it is a progressive aft action on the stick. A continuous aft pressure has to be applied as usual.


- At 20 ft a call out « RETARD » reminds the pilot to retard thrust lever. It is a reminder, not an order. Indeed with ATHR ON, SPEED mode is effective except if autoland (AP ON with LAND/FLARE). Therefore if you are late to retard the thrust levers in a MANUAL landing, the ATHR will add thrust during the Flare to keep the A/C on target speed. - In order to assess the Flare and the A/C position versus the ground, look out well ahead of the A/C.

[de facto]

...and the effort trophey goes to Nitpicker

[Trackdiamond]

Nitpicker 330

Mate! Your nitpick was spot on..except you left out one thing unpicked!...lateral corrections to maintain Track required....use of the handy TRACK DIAMOND!

Also has there anything been updated on Airbus FCTM regarding why the "retard" call silences after a coulke of reminders at 5ft? I guess the jockey is getting carried away looking for a greaser and floating away with power not retarded..confusing the computer sensor..why doesn't it scream "RETARD! Or GO AROUND!"??

[nitpicker330]

I'll have to look again about the Retard call.

With regards to Lateral control we could assume from their way of thinking that they use Rudder to control it.

[nitpicker330]

There is nothing new in the FCTM regarding the Retard call that I can see?

At 20 ft, the "RETARD" auto call-out reminds the pilot to retard thrust levers. It is a reminder rather than an order. When best adapted, the pilot will rapidly retard all thrust levers depending on the conditions, the pilot will retard earlier or later. However, the pilot must ensure that all thrust levers are at IDLE detent at the latest at touchdown, to ensure ground spoilers extension at touchdown.

There is the usual warnings section that details the RETARD call will happen if one Engine is in Reverse but the other thrust lever is not at Idle, RETARD will continue until you fix the condition.



However I did find yet another Reference to controlling IAS on approach using thrust.....

Yet more proof Noodle and 737Jock are way off base and need re-training:--

SUPP PROCEDURES POWER PLANT---


USE OF AUTOTHRUST IN APPROACH The pilot should use autothrust for approaches. On final approach, it usually gives more accurate speed control, although in turbulent conditions the actual airspeed may vary from the target speed, by as much as 5 kt. Although the changeover between auto and manual thrust is easy to make with a little practice, the pilot should, when using autothrust for the final approach, keep it engaged until he retards the thrust levers to idle for touchdown. If the pilot is going to make the landing using manual thrust, he should disconnect the A/THR by the time he has reached 1 000 ft on the final approach. If he makes a shallow flare, with A/THR engaged, it will increase thrust to maintain the approach speed until he pulls the thrust levers back to idle. Therefore, he should avoid making a shallow flare, or should retard the thrust levers as soon as it is no longer necessary to carry thrust, and if necessary before he receives the “retard” reminder. Although use of the autothrust is recommended for the entire approach, this does not absolve the pilot from his responsibility to monitor its performance, and to disconnect it if it fails to maintain speed at the selected value. Such monitoring should include checking on whether or not the managed speed, calculated by the FMGEC, is reasonable.

[737Jock]

First of all nitpicker I never said that speed for thrust is an incorrect statement. But the simple fact is that thrust for vertical speed neither is incorrect.

You can point as long as you want at the FCTM for thrust is speed definitions, and I can show you as many Principles of flight manuals that state that thrust controls vertical speed.
Both statements are correct, they are just simple descriptions of a more complex interaction.

You can continue your pissing competition with Noodle about which manual you would rather believe. As far as i'm concerned you are both wrong as much as you are both right.

Keep making up examples that fit your own argument. I can also counter that by saying you would not lower the nose close to the ground to recover the path if you get an updraft above the runway, nor would you raise the nose dramatically to stop a sink close to the ground. You either reduce or increase thrust, or change the rate at which you are changing the thrust (slower/faster). So at different stages we use different methods, doesn't mean that other methods don't work or that they are incorrect. or that an explanation from a different viewpoint is wrong.

Thrust is simply energy balancing. Thrust adds or decreases the energy of the aircraft. The pitch control determines if this energy change is converted into a speed change or a vertical speed change or both. Thrust and pitch continuously interact.
External factors can also add or decrease the energy of the aircraft, if we don't balance this external energy change by an equal opposite change in thrust energy. Then the pitch will either cause a speed change or a vertical speed change.

second of all I already said that airbus is not speedstable so you will always need to change pitch after thrust changes, or change thrust after pitch changes. Remember what speed stability is?
An airbus maintains its path, not its speed. Try some direct law flying!

[InSoMnIaC]

737Jock I think the problem lies in those 500hr flight instruction that you were talking about. Problly done in pistons.

What you are saying can be applied to a light prop driven aircraft which responds quickly to power changes and doesn't have very much momentum to overcome. However when we talk about heavy jets we have to consider the slow response time of the engines and the even slower effect that those engines have on the aircraft (as u have all that momentum to overcome).

This is why we use pitch. We do not use adding energy for refining and perfecting the flight path on the approach as it will take way to long for the aircraft to respond. We rather just convert some speed into altitude or visa versa and then worry about the speed (which has a built in margin anyway) by adding or reducing thrust.

All things being equal L= ROD=AoAxIAS. The easiest way to affect lift is by changing AoA (due to inertia and slower response of aircraft to change speed)

The easiest way to change AoA is by using that big arse elevator to change the relative airflow of those big arse wings.

Bloggs question is valid. Let me put it another way. If you are on short final and u get a speed reduction do you push the nose down first or add thrust and maintain the flight path with pitch. Its pretty straight forward. Dont try to complicate it.

by the way if your method works better airbus/boeing etc would have programmed the autopilot to chase speed on approach and the active ATHR mode would be GS (sounds silly to me)

[737Jock]

1/ Unreliable Airspeed checklist in the QRH containing Pitch and Thrust tables for Approach.

2/ Flying the BUSS on the Airbus is taught BY Airbus to hold a constant Pitch and Adjust Thrust to stay "in the green" ( correct AOA and therefore IAS for the Config )

So lets start with BUSS, BUSS tells us (or at least you do) to maintain pitch and use thrust to stay in the green.
So what happens when I'm descending and I maintain pitch at say 5 degrees nose-up and I add thrust:
1. vertical speed changes
2. airspeed changes
3. vertical speed and airspeed both change


Lets now look at the unreliable airspeed checklist. This checklist says that a decreasing pitch attitude indicates the aircraft is too fast, and that an increasing pitch attitude indicates the aircraft is slow.

Funny that BUSS tells us to maintain pitch attitude and keep in the green with thrust, whereas in an aircraft without BUSS we use the change in pitch attitude to determine if we are on speed or not.

[737Jock]

Insomniac, There is no problem.

I'm not saying that thrust for speed is incorrect, it works. But its still a simplified version of what actually happens.

Thrust is energy that can be added or removed from the airframe by pushing the thrust levers foward or aft. We use it to balance the forces on the aircraft.
If the aircraft is flying a stable path, vertical speed and airspeed do not change.
If in this stable flightpath I then add thrust (add energy) either the airspeed or the vertical speed will change until a new equilibrium (a new stable flightpath) is found. The pitch determines if the airspeed changes or if the vertical speed changes. Obviously this new equilibrium (flightpath) is not what we desire, its either too fast or too shallow.

There are also external factors that can increase or decrease the energy of the aircraft. An updraft will add energy to the airframe, if we don't do anything the pitch attitude will either convert this extra energy into airspeed (too fast) or into vertical speed (too shallow). This is obviously undesired so we need to restore our original stable flightpath. We can only do this by reducing the energy of the aircraft, by the same amount that was added by the updraft. Therefore we reduce thrust.

So when I encounter an updraft, I reduce thrust as I know I will need to decrease the energy of the aircraft to maintain the stable path.
If I encounter a downdraft I add thrust as I know I will need to invrease the energy of the aircraft to maintain the stable path.

Any examples where I'm still slowing down or speeding up are not stable flightpaths. Therefore I can utilise the energy in a different way.

[InSoMnIaC]

Correct however u are not considering that the larger the aircraft the longer it takes for this equilibrium to take effect. That is why we simply say stuff waiting for this equilobrium. We are more worried about out flight path at this stage so we maintain the flight path and then slowly recover the speed excursion with thrust

[737Jock]

I'm not saying anything about how long it takes. You can simply feel up and downdrafts by the seat of your pants. Therefore you can immediately add or reduce thrust as required, that there still might be a little speed excursion is hardly the point.
There is no reason to feel the updraft, push on the nose and then wait until you see a speed excursion before you reduce thrust. Nor is there a reason to feel the updraft, allow the vertical speed to reduce and then decrease thrust to increase the vertical speed.

In the flare the groundeffect reduces the energy required to maintain the flightpath, plus we want to alter the flightpath by reducing vertical speed. So in the flare we exchange airspeed for a reduced vertical speed and we reduce thrust because we need less energy due to the groundeffect.
Any additional external upsets in the flare require a change in energy/ a change in the rate of energy change, so we either reduce thrust slower or faster. And in extreme cases might even need to add power.

A computer can't anticipate, it can only react after the fact. Humans can anticipate.

Pitch controls both vertical speed and airspeed, thrust controls energy. However energy is not easy to quantify. Therefore energy can be linked to airspeed, but it can also be linked to vertical speed. Both airspeed and vertical speed are an indication of the energy of the aircraft.
Therefore both statements, thrust is speed and thrust is vertical speed are true.
The path is a combination of airspeed and vertical speed, so the statement that thrust is path is also true. In the end Pitch + Power = Performance.

I always said that we manipulate pitch and thrust simultaneously. And on top of that thrust often also has a direct effect on potch because its not delivered in the centerline.

[nitpicker330]

Thrust this, secondary effect that, pull this push that etc etc etc

You are making it way to complicated, sounds wonderful in THEORY if you are studying aerodynamics in the classroom!!

Mate at the end of the day you fly your jet the way you want to......me? I'm going to keep it simple and follow the manufactures recommendations as to how to fly THEIR Aircraft.

For one simple reason------LITIGATION, if something un desired should happen I will have less chance of being screwed over in the subsequent court of enquiry...
Sounds silly but at the end of the day it's our jobs on the line each and every time we strap in to the Jet.

Remember big brother is watching everything you do, they will know what inputs you made to the controls every step of the way.....

Anyway sounds to me like we probably do the same things although you don't realize it!!

[nitpicker330]

Back to the BUSS.

Below FL250 on descent you switch off all ADR's
Idle descent pitch will be around zero to stay in the green.
All Config changes are recommended to be done in level flight wings level.
We all know or should know approx pitch attitudes to hold level while configuring,,,,,,yes around 5 up give or take.

Setup 5 up and stay in the Green as you configure. Try to hold a fairly constant Pitch and take flaps as the green moves up the screen to keep it in the middle.....

Config 3 attained, hold pitch and add thrust hold it in the green until GS intercept ( hopefully you achieved Flap 3 as you intercepted the GS so you don't need to fly level too far ) then pitch down a little to keep on the GS and at the same time reduce Thrust to around 49% to stay in the green zone. The base figures should be pitch 4.9 thrust 49% N1. Vary the pitch to maintain the GS and thrust to keep in the green.

Down the slope, keep Pitch stable to hold the GS and adjust Thrust to stay in the Green

Land, kiss ground and complete tons of paperwork.

Simple

Works well that way, if you try to vary the pitch up and down AND change the thrust it gets complicated way fast!!

Still, you need to know approx Pitch attitudes to set to kick things off.


With regards to your comments regarding Non BUSS Aircraft, I believe you misunderstand the intent

QRH says--

FLYING TECHNIQUE TO STABILIZE SPEED: Adjust pitch in order to fly the required flight path. When target pitch is reached, flying intended flight path, adjust thrust to target. If the aircraft pitch tends to increase, aircraft is slow, then increase thrust; If the aircraft pitch tends to decrease, aircraft is fast

You set a Target Pitch and then see what happens, if the Pitch moves then ADJUST THRUST because it's either too much or too little to achieve the CORRECT IAS.

Therefore same as the BUSS, Pitch is the base line and your primary target, Thrust is then used to adjust to stabilized flight path ( and therefore IAS ) for what you are trying to do.

Indeed on Approach Flap 3 it's exactly the same, setup the required Pitch of 4.9 deg adjusting as required to keep the GS and set 49% N1 which should get the speed correct ( comparing IRS/GPS GS and tower winds to approximate the IAS ) remembering that you have a good margin in Flap 3 between VLS and VFE Flap 3 limit to stay inside. ( about 40 kt split )

[Steve the Pirate]

This has been a fun thread! What I want to know is, if I'm meant to adjust power to follow a glideslope, why do the manufactures insist on calling it a flight director pitch bar and not speed bar

As far as hearing RETARD 3 or 4 times during the flare goes (common on an A/THR approach) it's possibly due to the pilot not understanding that there's a heck of a lot of thrust lever movement required before he gets to the actual thrust value - he thinks as soon as he moves the levers from the CL detent he's reducing the thrust which, unless he had climb thrust on during the flare (unlikely), he's not. As for manual thrust approaches, it could be a number of reasons but whatever the reason he will be compromising landing performance.

I'm with nitpicker and Bloggs on this one. Power/thrust for glideslope works well in small aircraft with near-instantaneous thrust response and little inertia whereas it's not such a practical method of maintaining a glideslope on a heavy jet.

[Capn Bloggs]

Originally Posted by 737Jock

I can also counter that by saying you would not lower the nose close to the ground to recover the path if you get an updraft above the runway, nor would you raise the nose dramatically to stop a sink close to the ground. You either reduce or increase thrust, or change the rate at which you are changing the thrust (slower/faster).

If you get an updraft "above the runway" (I assume you have started to flare - by easing back the stick back with power coming off) you don't just pull the power back and wait! You'll either land very long or very slow/hard. You decide either to lower the nose again if you have runway space and height (add power if getting slow before touchdown) or go around.

If you get a bad sink close to the ground you would most certainly raise the nose (depending on type/tail clearance, of course); put the power up as well if it's a significant pitch change. By the time these donks spin up to meaningful thrust you'd have hit the deck hard if all you did was maintain the pitch attitude you had before the sink hit you. Obviously, the lower it hits, the less options you have, but we're moving away from the main argument which is what you use to control what during a somewhat normal approach.

Whether deliberate or not, you are continually mixing up the scenarios:

So lets start with BUSS, BUSS tells us (or at least you do) to maintain pitch and use thrust to stay in the green.
So what happens when I'm descending and I maintain pitch at say 5 degrees nose-up and I add thrust:

We're not talking (never have been) about general descents where pitch is used to control the speed (fixed power ie idle) and obviously if you add a bit of power, the rate of descent will reduce (secondary effect of controls); we're talking in this thread about being stabilised coming down final and flare with a known vertical path that you must stay on.

A computer can't anticipate, it can only react after the fact. Humans can anticipate.

So how does autoland work then?

[737Jock]

autoland doesn't anticipate bloggs.

The answer to what happens is what I wrote. You can try to twist and turn what I said in all kinds of directions, but I never said that thrust for speed doesn't work. I said its an incomplete simplification, and that also goes for thrust is vertical speed. Yet for some reason you don't want to accept its a simplification.
That you and nitpicker find the more complex version (which is also incomplete) too complicated to understand is not my problem.

Be my guest and fly your aircraft like an autopilot that only acts reactive.

[Capn Bloggs]

737jock, let me ask the question another way. Give us an example of how a human could anticipate whereas the AP on an autoland can't.

I do actually understand every bit of your theories but I choose to ignore them, and criticise them, because not only do they fly in the face of basic aerodynamics for normal jets (not naval fighters) during the landing phase, they don't work satisfactorily unless you're trick-flying your 737 with it's pitch/power couple.

Further, your arcane points on energy really are for the theorists and would do nothing to help a newbie. You did say yourself "thrust controls energy. However energy is not easy to quantify. Therefore energy can be linked to airspeed, but it can also be linked to vertical speed."

[737Jock]

Back to the BUSS.

Below FL250 on descent you switch off all ADR's
Idle descent pitch will be around zero to stay in the green.
All Config changes are recommended to be done in level flight wings level.
We all know or should know approx pitch attitudes to hold level while configuring,,,,,,yes around 5 up give or take.

Setup 5 up and stay in the Green as you configure. Try to hold a fairly constant Pitch and take flaps as the green moves up the screen to keep it in the middle.....

Config 3 attained, hold pitch and add thrust hold it in the green until GS intercept ( hopefully you achieved Flap 3 as you intercepted the GS so you don't need to fly level too far ) then reduce Thrust to around 49% to stay on the GS.

Down the slope, keep Pitch stable and adjust Thrust to stay in the Green

Land, kiss ground and complete tons of paperwork.

Simple

Works well that way, if you try to vary the pitch up and down AND change the thrust it gets complicated way fast!!

Still, you need to know approx Pitch attitudes to set to kick things off.


With regards to your comments regarding Non BUSS Aircraft, I believe you misunderstand the intent

thanks for the lecture? don't know where this came from, but I can assure you I don't misunderstand the intent.

Let me quote from the QRH:

If the aircraft pitch tends to increase, aircraft is slow, then increase thrust;
If the aircraft pitch tends to decrease, aircraft is fast, then decrease thrust.

So according to you in BUSS we maintain the pitch constant and stay in the green with thrust.
Whereas on aircraft without BUSS, we judge the change in pitch to determine if we are slow or fast.

You see the bar that replaces the speedscale is in fact not a speedbar. Its an AOA bar.
FCTM:

The BUSS is displayed on both PFDs. It is based on Angle Of Attack (AOA) information, and enables to easily and safely fly the aircraft without any valid airspeed indication. The BUSS enables to fly the aircraft in the entire flight domain while observing the design limits.

You said earlier that you keep the path with pitch, so in BUSS you clearly fly differently as you keep the pitch fixed. And you even explain that varying the pitch would make it too messy.

Now I ask you again, if we use your method to fly in BUSS by maintaining a fixed pitch and staying in the green (AOA) with thrust, what are you changing? Speed, vertical speed or both?

-----

You constantly keep talking about changing configuration, slowing down on the glideslope etc. You realise that you are reducing the energy of the aircraft right?
I hope you also realise that slowing down does not fall under the definition of a stable flight.

For a flight to be stable it means that all forces are balanced. You slow down because the combined force vectors acting rearward, are bigger then the combined force vectors acting forward. Only when they are equal your speed will remain the same.
Just because you are going down 3 degrees does not make the flight stable.

[737Jock]

No you don't understand Bloggs. That much is very clear simply from the word trick-flying. Its not trick flying, its aerodynamics.
It becomes even more clear when you differentiate aerodynamics by size. Physics don't change by size.

you can try all you want to put me and noodle in the same camp, but what I said was that both camps are right. The truth of what happens is more complicated. But as a teacher you should always know a bit more the. the student right? what if he doesn't understand your thrust is speed way of flying. You give up or try a different approach?

I'm sorry but I'm not gonna dumb down the truth because all the information you can grasp should be understandable for a newbie.

That you don't like to hear that other people are right besides you is a problem you need to discuss with your own ego.

I'll discuss further with nitpicker if you don't mind.