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CVividasku
28th Jul 2023, 00:02
Hello,

I've been flying airbus single aisle for 3 years now but never any other airliner type.
In the past three days, I've had to go around twice because of the GS mini function of the airbus, or rather its absence on other types.

- We go into a tight sequence at a major airport
- We're 2.5-3nm behind a smaller E170 airplane, with a lot of headwind
- We reduce speed as much as we can but the E170 goes about 130kt (or even less?) while with headwind, our Vapp goes from 140kt to 160kt
- We catch up with the previous airplane and are instructed to go around..
- If every pilot like myself has to perform a go around every three days, the airline might go bust

Which other airplane brands have a function similar to that of airbus ?
I'm particularly interested in the A220, ERJ, Boeing.

Thanks

gearpins
28th Jul 2023, 03:48
Hello there,
Some points to note-

GS mini function allows you to fly a relatively constant ground speed.
Most major airport now use time based seperation - during strong headwind it is normal to see seperations of 2-2.5nm. not an issue.
Most likely a one off event - I wouldnt be concerned.
https://www.youtube.com/watch?v=2jBvbpbq0SM

763 jock
28th Jul 2023, 03:55
Hello,

I've been flying airbus single aisle for 3 years now but never any other airliner type.
In the past three days, I've had to go around twice because of the GS mini function of the airbus, or rather its absence on other types.

- We go into a tight sequence at a major airport
- We're 2.5-3nm behind a smaller E170 airplane, with a lot of headwind
- We reduce speed as much as we can but the E170 goes about 130kt (or even less?) while with headwind, our Vapp goes from 140kt to 160kt
- We catch up with the previous airplane and are instructed to go around..
- If every pilot like myself has to perform a go around every three days, the airline might go bust

Which other airplane brands have a function similar to that of airbus ?
I'm particularly interested in the A220, ERJ, Boeing.

Thanks
Have you tried pulling the knob?

Check Airman
28th Jul 2023, 05:35
As far as I know, only FBW Airbus planes have that feature.

FLX/MCT
28th Jul 2023, 08:51
I can confirm there is no GS mini on the A220, ERJ and the Boeing models I know.
On the 777 the A/T has some kind of schedule which adds thrust quicker than it reduces resulting in a somewhat higher speed in gusty/dynamic wind conditions but so far the excess speed resulting is to a smaller extent than GS mini and also for a shorter duration.

vilas
28th Jul 2023, 18:11
Hello,

I've been flying airbus single aisle for 3 years now but never any other airliner type.
In the past three days, I've had to go around twice because of the GS mini function of the airbus, or rather its absence on other types.

- We go into a tight sequence at a major airport
- We're 2.5-3nm behind a smaller E170 airplane, with a lot of headwind
- We reduce speed as much as we can but the E170 goes about 130kt (or even less?) while with headwind, our Vapp goes from 140kt to 160kt
- We catch up with the previous airplane and are instructed to go around..
- If every pilot like myself has to perform a go around every three days, the airline might go bust

Which other airplane brands have a function similar to that of airbus ?
I'm particularly interested in the A220, ERJ, Boeing.

Thanks
Perhaps a hasty conclusion. As pointed out you can't be closing in when your GS is constant. Other aircraft use fixed additive to VLS. Let's say winds are 20kt gusting to 30, the the additive will be half wind+full gust= 10+10=20. Vapp with this addition will be flown even if wind drops and you can't reduce below Vapp. That will make you close in on the traffic. GS mini will reduce Vapp if wind drops. So definitely GSmini not at fault. Last, you couldn't have discovered in 3 years what nobody else discovered in 34 years. Could you?

HOVIS
28th Jul 2023, 18:16
https://youtu.be/58s9ymI14SU

FlightDetent
28th Jul 2023, 19:27
Please.

GS mini kicks on the difference between the tower-reported runway wind and the actual wind. It only manifests itself when there is a large difference between the two.

Case on a northerly runway, coastal perhaps. QFU 000.

W/V TWR-RWY = 300/12 kts (headwind 6)
airborne w/v @1300 ft = 340 / 45 (headwind 40)

Vapp-final 132 kts and:
on a conventional calculation: Vtarget = 135 kts (TAS 138 ish -> GS 98)
for a GS-mini bus: Vtarget = 168 kts (TAS 175 ish --> GS 135).

No surprise the bus in-trail would catch up by 1 mile by the time he descend from 1300 ft to the threshold (2 mins at 3 deg standard 700 fpm).

If I could see the situation unfolding, my choice is to speed select Vref + 5 (ATHR) + 5 (pilot) and keep going. At one point the headwind disappears but A/THR should catch-up well inside the 10 kt margin prepared.

Yes, I had a TGV overtake me before the Airbus time. :E

Jonty
28th Jul 2023, 19:49
Have you tried pulling the knob?

Do this. Itís not rocket science.

Vessbot
28th Jul 2023, 22:03
Perhaps a hasty conclusion. As pointed out you can't be closing in when your GS is constant.
But yes you can, if the other guy's GS is not constant. And you described just such a scenario yourself, concluding with:
That will make you close in on the traffic.
before reversing again:
So definitely GSmini not at fault.?

vilas
29th Jul 2023, 11:37
But yes you can, if the other guy's GS is not constant. And you described just such a scenario yourself, concluding with:

before reversing again:?
As long as two aircraft follow different philosophies some increase decrease of separation is not avoidable. But it would be transient. May be ATC spacing was too tight or the aircraft ahead may have slowed down. Because so many buses flying for so long it's not been an issue.

Meikleour
29th Jul 2023, 15:34
Airports like LHR and LGW routinely use airspeeds commanded by ATC to achieve their spacing so, to gayly use GSmini in those situations of high winds would interfere with that spacing. Why not just revert to GSmini managed speed once #1 to land?

I once operated a A340 into LHR when the 2,000 wind was 70kts and the surface wind 38kts. ATC commanded speed gave us a groundspeed of 90kts at one stage!

Vessbot
29th Jul 2023, 17:45
As long as two aircraft follow different philosophies some increase decrease of separation is not avoidable. But it would be transient. May be ATC spacing was too tight or the aircraft ahead may have slowed down. Because so many buses flying for so long it's not been an issue.

Closure rate is transient, but distance change is not. Once the airspeeds return to being the same, there is no mechanism to return the distance back to the original.

vilas
29th Jul 2023, 18:11
Closure rate is transient, but distance change is not. Once the airspeeds return to being the same, there is no mechanism to return the distance back to the original.
ATC is monitoring the difference or seperation. They may ask you to further slow down which can be done in select speed. But with GSmini so much active means it's very strong gusty wind should ATC keep two aircraft aircraft so close? You could decline.

CVividasku
30th Jul 2023, 13:36
Good question. At my airline I've never seen anyone override the gs mini with a slower selected speed.
However i couldn't find anywhere that it was forbidden to do so.

Maybe gs mini has not been such a problem because pilots are overriding it when needed.

FlightDetent
30th Jul 2023, 21:40
Indeed.

When asked to slow down to final speed, as a request to avoid things falling apart on the ATC side,

​​​​​​What the MCDU says is my target, with reasonable precautions as per above.

Check Airman
31st Jul 2023, 00:24
Airports like LHR and LGW routinely use airspeeds commanded by ATC to achieve their spacing so, to gayly use GSmini in those situations of high winds would interfere with that spacing. Why not just revert to GSmini managed speed once #1 to land?

In my relatively limited experience, LHR seems to routinely give landing clearance at very low altitude (200-300ft). Not the ideal time for a big airspeed change.

Check Airman
31st Jul 2023, 00:32
This topic brings up a question I'd considered a while back.

Is it wise to override GSmini? I can see 2 different sides to this...

1. Wouldn't allowing the automation to do its thing be the best in this situation? If you were in a conventional airplane, and your Vapp turned out to be Vref+20, would you fly a slower speed just for spacing?

2. At some point, you're going to have to slow down, otherwise you may be in for a very long landing, so you're better off overriding GSmini.

I've never had to do it, but for those who have, at what point do you ignore the managed speed, and fly your own speed, and what speed do you opt to fly? Let's assume Vls is 135, with a Vapp of 140.

Vessbot
31st Jul 2023, 01:09
Isn't there a specified approach speed to set for when not using GSmini? Honest question from outside looking in.

AerocatS2A
31st Jul 2023, 06:09
This topic brings up a question I'd considered a while back.

Is it wise to override GSmini? I can see 2 different sides to this...

1. Wouldn't allowing the automation to do its thing be the best in this situation? If you were in a conventional airplane, and your Vapp turned out to be Vref+20, would you fly a slower speed just for spacing?

2. At some point, you're going to have to slow down, otherwise you may be in for a very long landing, so you're better off overriding GSmini.

I've never had to do it, but for those who have, at what point do you ignore the managed speed, and fly your own speed, and what speed do you opt to fly? Let's assume Vls is 135, with a Vapp of 140.

I would ignore managed speed in very strong headwinds when it takes me too close to the bricks. 5 knot buffer isnít enough sometimes. I might select speed if ATC want something specific and Iím happy that the selected speed puts us comfortably in the middle of the envelope. Mostly I let GS mini do itís thing, I think itís great.

vilas
31st Jul 2023, 07:20
Wouldn't allowing the automation to do its thing be the best in this situation? If you were in a conventional airplane, and your Vapp turned out to be Vref+20, would you fly a slower speed just for spacing?
The answer is OFFCOURSE NOT. Unable is the message to ATC. ATC may have it's requirements but in turbulence pilot has his own which have to override ATC. If you fly select speed or fly conventional aircraft then half wind+full gust is the lowest limit you can fly at. VFE and Vapp is the band ATC can only ask you fly within.

Check Airman
31st Jul 2023, 07:27
I would ignore managed speed in very strong headwinds when it takes me too close to the bricks. 5 knot buffer isnít enough sometimes. I might select speed if ATC want something specific and Iím happy that the selected speed puts us comfortably in the middle of the envelope. Mostly I let GS mini do itís thing, I think itís great.

Thanks for your input. At what point would you go back to managed? Would you land in selected speed?

vilas
31st Jul 2023, 07:29
Isn't there a specified approach speed to set for when not using GSmini? Honest question from outside looking in.
Since it is expected to let GSmini do it's thing the formula for specific select speed is not given but why should it be different than say 737? Half wind+full gust that's what should be flown.

Check Airman
31st Jul 2023, 07:31
Isn't there a specified approach speed to set for when not using GSmini? Honest question from outside looking in.

The FMS will display Vref and Vref+5. GSmini works on top of that. SOP is to use it, and you canít really turn it off. Think of the way your ECON speed changes as conditions change. GSmini is like flying an approach in ECON.

ScepticalOptomist
31st Jul 2023, 09:09
The FMS will display Vref and Vref+5. GSmini works on top of that. SOP is to use it, and you canít really turn it off. Think of the way your ECON speed changes as conditions change. GSmini is like flying an approach in ECON.

Sounds like the aircraft is doing the thinking at a time when the pilot should be.

AerocatS2A
31st Jul 2023, 11:36
Thanks for your input. At what point would you go back to managed? Would you land in selected speed?
Just once the condition thatís making use selected speed has gone. I donít fly to places with much ATC speed control so Iíve never had to use selected because managed was too fast, thatís a hypothetical example of when Iíd use it. As for getting close to the bricks, Iíve had occasion when a strong wind at 2000í has had GS mini giving a high speed target. In this case Iíd go back to managed once out of the worst of the wind. That said, the function is there for good reason, it protects against a dramatic loss of energy when moving through shear layers, so I very rarely use selected for long.

CVividasku
31st Jul 2023, 12:33
Being only copilot I can only suggest the idea to captains, but I don't see a problem in overriding GS mini in the conditions that we flew through.
Steady, well established 30kt wind at altitude, gradually and nicely decreasing to a fixed value between 10 - 15kt on ground, I don't see any problem with a Vls+5 approach speed. (VLS+8 actually including the vpilot)
As long as there isn't anything forbidding it in the OM A or B, nobody has a say apart from the captain.

If it can avoid a third go around in less than 6 flights into this particular airport, we will do it.

GS mini does a nice job in harsh turbulence, or light windshear conditions. This was not the case. It was increasing speed for the sake of it, with no added benefit.
Also my reports went through our airline services, they may come back with an answer.

vilas
31st Jul 2023, 13:12
It was increasing speed for the sake of it, with no added benefit.
​​​​​​​It cannot do it without actual wind pushing the speed as it does even in select speed. Only difference in select speed ATHR reduces thrust to get it back, in GSmini thrust increases to maintain the increase.

Uplinker
31st Jul 2023, 13:51
Interesting discussion. The Airbus FBW and Boeing Vapp logic work in opposite directions in varying winds; With an increased HW gust, Airbus will increase thrust and IAS, (to maintain ground speed), Boeing will decrease thrust and IAS, (to maintain airspeed).

So given a gust, the Airbus will maintain its "place" on approach; whereas the Boeing will "move back" with a HW gust and "forwards" for a TW gust.

Always nervous when folk talk about overriding Airbus GS Mini, which could reduce safety margin in the event of an unexpected gust or wind drop. Some think the Airbus does the wrong thing or gets "out of phase", because it increases thrust and IAS with increased HW gust, (and vice versa). which is the opposite way round to "conventional" aircraft

Vessbot
31st Jul 2023, 17:01
The FMS will display Vref and Vref+5. GSmini works on top of that. SOP is to use it, and you canít really turn it off.
All the other posts seem to imply that selecting (pulling) speed, turns it off?

Check Airman
31st Jul 2023, 17:11
All the other posts seem to imply that selecting (pulling) speed, turns it off?

I was unclear. You canít turn it off in the sense that itís always operating in the background, calculating what your speed should be. You can always fly the speed you want by selecting it, or disconnecting the autothrust.

Uplinker
31st Jul 2023, 17:49
But if you do override GS Mini and select a fixed speed, or use manual thrust and ignore the IAS bug increases; remember that you could get dangerously close to the stall in gusty conditions, unless you add an additional safety factor to the speed you select.

Then of course, you will have to check your landing distance calculations for the additional speed you have added.

FlightDetent
31st Jul 2023, 18:09
6 out of 10 last post show insufficient understanding or failing memory of what GSmini is, how it works and what it does to the plane.

(Though I did not read AerocatS2A's contribution since I learned to agree with him on avatar value.)

The rest of you, please be gentle at each other, everyone is missing a bit.

E.g., no - upon arrival of front gust it does not add thrust.

​​

TopBunk
31st Jul 2023, 22:07
FWIW, I was LHR based for the vast majority of my career before retirement, and flew the A320 family for over 4 years, the rest of my career being on Boeings 737 and 747..

I recall being very happy in the LHR regime of 210, 180 and then 160 to 4dme on all types I flew.

The only times it caused concern was on the A320 in very strong headwinds when reaching 4dme at 160 and pressing managed speed resulted in a speed increase on occasion to 170+,

I learned from that and whenever another aircraft was close ahead - usually, used selected speed inside of 4d at an appropriate value - you won't fall out of the sky!

CVividasku
1st Aug 2023, 01:44
The FMS will display Vref and Vref+5. GSmini works on top of that. SOP is to use it, and you canít really turn it off. Think of the way your ECON speed changes as conditions change. GSmini is like flying an approach in ECON.
Our airline does not have any SOP like so.
It is allowed to fly VLS even in gusty conditions (not advisable, however, the conditions on the two said days were not gusty at all)
I recall being very happy in the LHR regime of 210, 180 and then 160 to 4dme on all types I flew.
I think we can all agree that French ATC allowing a trafic to reduce to 130kt (IAS) at 15 miles final is the underlying problem here.

Uplinker
1st Aug 2023, 14:46
E.g., no - upon arrival of front gust it does not add thrust.
From Airbus A320/321 FCOM:
GROUND SPEED MINI FUNCTION PRINCIPLEThe objective of the Ground Speed Mini function is to take advantage of the aircraft inertia, when the wind varies during the approach. This objective is achieved by providing the adequate indicated speed target (i.e. the managed speed target represented by the magenta triangle). When the aircraft flies this indicated air speed target, the energy of the aircraft is maintained above a minimum level ensuring aerodynamic margins versus stall.

During the approach, the FG continuously computes the managed speed target in order to take into account the gusts or wind changes.

my bold

I might be missing something, but am struggling to understand how the aircraft would follow an increased managed speed target from GS Mini, without increasing the thrust?

Or maybe my semantics are in question? With a gust, the FG computes a new managed speed target, which the auto-thrust follows, (if it is engaged). i.e. GS Mini itself does not add thrust, but it dynamically changes the managed speed bug, which then causes the auto-thrust to add thrust if required. :ok:

Denti
1st Aug 2023, 15:53
The calculated GS mini will increase, but with a gust the thrust usually does not increase as the gust will be the cause of an increased speed anyway. Once the gust is over the GS mini target will decrease, as will the indicated airspeed. Now, as always, things are not perfect, so there will be some play on thrust, but actually not all that much.

It helps to fly a few approaches in gusty weather using GS mini on manual thrust. It is surprising how little thrust changes there are.

Uplinker
2nd Aug 2023, 12:54
??? Sorry, I don't get you at all. HW gust needs increased thrust to follow the increased GS Mini IAS demand to maintain the groundspeed.

I grant you, the system can seem a bit lively in gusty conditions, which alarms some pilots.

AerocatS2A
2nd Aug 2023, 13:14
??? Sorry, I don't get you at all. HW gust needs increased thrust to follow the increased GS Mini IAS demand to maintain the groundspeed.

I grant you, the system can seem a bit lively in gusty conditions, which alarms some pilots.
Initially the thrust does not need to increase to follow the speed target because the gust itself has caused the aircraft to follow the speed target. Whether the thrust comes up subsequently depends on how transient the gusts are. The gustier conditions would tend to result in less auto thrust activity while descending through different strengths of relatively steady wind will result in the speed target remaining elevated for prolonged periods and the thrust will need to adjust to maintain it. Thereís also the fact that GS mini has been nerfed somewhat in the NEO aircraft so the system is less ďactiveĒ in those.

Uplinker
2nd Aug 2023, 13:53
Ah. I don't know about the NEO, sadly.

sonicbum
2nd Aug 2023, 14:29
A refresher

Why is there a different Ďkí factor for ground speed mini depending on the aircraft model (https://safetyfirst.airbus.com/control-your-speed-during-descent-approach-and-landing/)

FlightDetent
2nd Aug 2023, 14:32
??? Sorry, I don't get you at all. HW gust needs increased thrust to follow the increased GS Mini IAS demand to maintain the groundspeed.

I grant you, the system can seem a bit lively in gusty conditions, which alarms some pilots.

No, brother. You are completely clueless about the dynamics. Ox/cart and all.

Let's agree words such as 'I grant you' be restricted to people who had seen the real thing unfold and work live no less than 2 years ago, bare own eyes.

FlightDetent
2nd Aug 2023, 14:35
Ah. I don't know about the NEO, sadly.Bloody nothing to do with the engine, within the scope disussed.

vilas
2nd Aug 2023, 17:13
6 out of 10 last post show insufficient understanding or failing memory of what GSmini is, how it works and what it does to the plane.

(Though I did not read AerocatS2A's contribution since I learned to agree with him on avatar value.)

The rest of you, please be gentle at each other, everyone is missing a bit.

E.g., no - upon arrival of front gust it does not add thrust.

​​
https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/1080x1723/screenshot_20230802_213929_2_de229869025165a8e7a04b3ca3d6be1 4815d5143.png

AerocatS2A
2nd Aug 2023, 19:03
Uplinker It only accounts for 1/3 the difference between the tower wind and actual wind.

J.L.Seagull
3rd Aug 2023, 13:52
Let me try and explain this as simply as I can. The philosophy behind GSmini has nothing to do with transient gusts. It's about maintaining an acceptable kinetic energy level (ground speed) and potential energy level (remaining thrust available) AT TOUCHDOWN.

Picture this. You're at 1000ft and you have a headwind of 65kts. Tower reported wind is just 20kts headwind. The 65kt headwind stays until you're 250ft AGL. Then in a span of a few seconds, you suddenly lose 45kts headwind and consequently your IAS too.

Now you're uncomfortably close to your stalling speed, and the engines are almost at max thrust trying to make up for the lost airspeed. You don't have the airspeed to land safely, nor do you have the thrust to carry out a safe go-around so close to the ground.

GSmini mitigates this by adding extra speed when it anticipates such a condition by measuring the difference between current wind during the approach and wind entered in the MCDU
​​​
PS If you think I'm making up such wind conditions, I'm not. It's just a regular day at UGTB or OBBI :8

Uplinker
3rd Aug 2023, 16:37
No, brother. You are completely clueless about the dynamics. Ox/cart and all.

Let's agree words such as 'I grant you' be restricted to people who had seen the real thing unfold and work live no less than 2 years ago, bare own eyes.

Gosh, thank you so much !

Now, was there really any need for that outburst, or would a careful explanation with diagrams perhaps have been more appropriate in Tech Log - where most of us like to expand our learning?

I never claim to know everything and I admit that I only have about 8,500 hours and 14 years on Airbus FBW, so have only observed GS mini a thousand times or so. But whatever.

As for the NEO; No, obviously nothing to do with the engines, but I thought someone said it has modified GS Mini laws?

vilas
3rd Aug 2023, 17:13
Neo word drags your attention to engine away from aerodynamics. Neos have Sharklets and LIP Lift Improvement Package that has improved engine strakes and better slat seals improving lift and reducing drag.This when closer to ground makes it difficult to drop the excess speed of GSmini. That's why in Neos the GSmini uses only 33% of difference in experienced wind and reported surface wind which makes it manageable to reach Vapp. Only disadvantage is autothrust activity increases.

CayleysCoachman
3rd Aug 2023, 21:36
Oh my word. Itís an aircraft. It has thrust and drag, weight and lift. It has flying controls. You can pitch up and down, bank left and right, and control or use yaw. You can take fully manual control of the thrust, like you did in your PA28/C152. If you do those things you have no issue with the French electric jet trying to be too clever. Youíre the boss, not some programmer in 1980s Toulouse.

172_driver
4th Aug 2023, 10:12
It's almost funny. The B737 FCTM has the following two sentences about the scenario discussed, that GSmini is supposed to handle:

When using the autothrottle, position command speed to VREF+5 knots. Sufficient wind and gust protection is available with the autothrottle connected because the autothrottle is designed to adjust thrust rapidly when the airspeed drops below commanded speed while reducing thrust slowly when the airspeed exceeds commanded speed. In turbulence, the result is that average thrust is higher then necessary to maintain command speed. This results in an average speed exceeding command speed.

That's it folks, Vref+5 :ok:

vilas
4th Aug 2023, 10:47
It's almost funny. The B737 FCTM has the following two sentences about the scenario discussed, that GSmini is supposed to handle:

When using the autothrottle, position command speed to VREF+5 knots. Sufficient wind and gust protection is available with the autothrottle connected because the autothrottle is designed to adjust thrust rapidly when the airspeed drops below commanded speed while reducing thrust slowly when the airspeed exceeds commanded speed. In turbulence, the result is that average thrust is higher then necessary to maintain command speed. This results in an average speed exceeding command speed.

That's it folks, Vref+5 :ok:
Not so easy. B737 800 Vapp for 63 ton Flaps 30, 146kt. which is 8kts higher than A320 flap3. Boeing Autothrottle switched off with AP. And Boeing speed additives are not just 5kts but half wind+Full gust. i.e. for surface wind of 20kts gusting to 30kts is 10+10=20kts. Out of that the steady half wind needs to be bled off approaching flare which rarely anybody does.

172_driver
4th Aug 2023, 13:06
True, A/T off requures a bit more thinking.
Vref + 10-15 knots works pretty well too if it's windy. To be bled off whenever your gut tells you to. Usually by starting retarding when RA comes alive at 50 ft.

Uplinker
6th Aug 2023, 19:48
Oh my word. Itís an aircraft. It has thrust and drag, weight and lift. It has flying controls. You can pitch up and down, bank left and right, and control or use yaw. You can take fully manual control of the thrust, like you did in your PA28/C152. If you do those things you have no issue with the French electric jet trying to be too clever. Youíre the boss, not some programmer in 1980s Toulouse.

See? This is exactly what worries me: People who do not understand how GS Mini works, but nevertheless think they can override it and fly more safely by ignoring it.

Those designers, engineers and test pilots in Toulouse are far, far cleverer than you or I, and they have done a fantastic job with the Airbus FBW. An order of magnitude better than Boeing, with their MCAS, for example. (And even their supposedly FBW B777 still has pitch trim pickle switches).

Vessbot
6th Aug 2023, 20:11
So far there's speculation over...
- if there's a reason the wind additive might be different than another manufacturer specifies
- whether good airmanship implies you can select Vapp
- design engineers being smarter than line pilots
- maybe some other things I missed

... but still no word on simply whether SOP allows for selecting Vapp. I'd have thought a matter like this would be very straightforward... pretty much yes/no with a manual reference?

As an aside,

... supposedly FBW B777 still has pitch trim pickle switches.
FBW doesn't necessarily mean FBW with the control law that Airbus uses.

CVividasku
6th Aug 2023, 20:22
As long as there isn't anything preventing you from flying Vapp, I don't see why you would be forced to used managed speed.

My mind has now moved on to something else. The use of reversers (thrust lever management) in case of inoperative reversers (all inop)
The FCTM is very very unclear about this. I will let whoever wants to read it and be surprised (or not)

CayleysCoachman
6th Aug 2023, 22:07
See? This is exactly what worries me: People who do not understand how GS Mini works, but nevertheless think they can override it and fly more safely by ignoring it.

Those designers, engineers and test pilots in Toulouse are far, far cleverer than you or I, and they have done a fantastic job with the Airbus FBW. An order of magnitude better than Boeing, with their MCAS, for example. (And even their supposedly FBW B777 still has pitch trim pickle switches).

and in turn, THIS is what worries me, alongside the compete faith Toulouse has in their competence. Need I list all the famous FBW crashes, all the expert critique of the weaknesses designed into the HMI, all the near-misses, all the major errors with Airbus signatures at the bottom line, the famous letter saying there was no need to train FBW airliner pilots in unusual attitude recoveries, etc etc? I could go on. I know exactly how GS MINI is meant to work; I also know that unquestioning trust in technology dooms us to failure. If you need something like that to keep from crashing, you really need to be looking deeper.

sonicbum
7th Aug 2023, 08:34
As long as there isn't anything preventing you from flying Vapp, I don't see why you would be forced to used managed speed.

My mind has now moved on to something else. The use of reversers (thrust lever management) in case of inoperative reversers (all inop)
The FCTM is very very unclear about this. I will let whoever wants to read it and be surprised (or not)

Q1. SOP
INITIAL APPROACH:
(Ö) MANAGED SPEED....................................................... ......................CHECK ▏ PF
If ATC requires a particular speed, use selected speed. When the ATC speed constraint no longer applies, return to managed speed.

Q2.
AT LEAST ONE REVERSER OPERATIVE
If at least one reverser is operative, the general recommendation is to select the reverser thrust on both engines during rejected takeoff (RTO) and at landing, as per normal procedures.

NO REVERSERS OPERATIVE
If no reversers are operative, the general recommendation is to not select the reverser thrust during RTO and at landing. However, the PF still sets both thrust levers to the IDLE detent, as per normal procedures.


TAM 3054 accident.
After this accident the procedure changed and so did the wording as highlighted above.

From the report:
The FDR transcript shows that immediately after the warning, the flight computer recorded the left thrust lever being retarded to the rear-most position, activating the thrust reverser on the left engine, while the right thrust lever (controlling the engine with the disabled thrust reverser) remained in the CL position.

So all Airbus is trying to tell you is: do not forget to close the thrust levers when you land. It may sound obvious to 99.9% of the pilots but as there was an accident involved, lawyers got in the way.

With both reverser inoperative if you do select IDLE REVERSE the FADEC will command an increased N1 which will adversely affect your landing distance as there will be no reverse deployment.

With 1 REV INOP, same will happen on the Inoperative reverser but the operative one will compensate and the loss in performance is negligible. Thatís why you can handle your reverse as you would normally do with no failures/MEL.

p.s. Do not confuse IDLE DETENT with IDLE REVERSE.

172_driver
7th Aug 2023, 11:15
See? This is exactly what worries me: People who do not understand how GS Mini works, but nevertheless think they can override it and fly more safely by ignoring it.

Those designers, engineers and test pilots in Toulouse are far, far cleverer than you or I, and they have done a fantastic job with the Airbus FBW. An order of magnitude better than Boeing, with their MCAS, for example. (And even their supposedly FBW B777 still has pitch trim pickle switches).

I am not really sure what you're getting at here. Manual speed additives have been used for a century soon and as far as I know no aircraft has ever stalled on approach due to inappropriate speed additives? You put a lot of faith in software developers. Now I am an airline pilot, but I also develop software and work closely with developers far better than me, their mindset is very different from that of a pilot (as I know 'pilots'). In software features are added because they're cool, not because they're necessarily asked for or needed by the end user. Now this is my opinion, but modern planes are killing the skill of being a pilot. I am talking fundamental skills. Do modern pilots understand they need added back pressure on the yoke/stick when entering a bank? Do they understand you need to trim in the aircraft in pitch whenever speed changes?

I know this thread is about GSmini, but I couldn't help myself responding to your glorification of Airbus designers and engineers. Granted, they're top line in what they're doing. Doesn't necessarily mean their system is the only way that works. I am more worried about the disconnect between pilots and the air, come future.

CVividasku
7th Aug 2023, 13:12
With both reverser inoperative if you do select IDLE REVERSE the FADEC will command an increased N1 which will adversely affect your landing distance as there will be no reverse deployment.
We asked airbus about that and we got a very prompt answer.
The FADEC will increase N1, but only for a very short time, as it will detect the reverser doors not open and go back to normal idle.
Still a bad idea to have this transient increase in thrust.

Uplinker
8th Aug 2023, 02:17
and in turn, THIS is what worries me, alongside the compete faith Toulouse has in their competence. Need I list all the famous FBW crashes, all the expert critique of the weaknesses designed into the HMI, all the near-misses, all the major errors with Airbus signatures at the bottom line, the famous letter saying there was no need to train FBW airliner pilots in unusual attitude recoveries, etc etc? I could go on. I know exactly how GS MINI is meant to work; I also know that unquestioning trust in technology dooms us to failure. If you need something like that to keep from crashing, you really need to be looking deeper.

I am not really sure what you're getting at here. Manual speed additives have been used for a century soon and as far as I know no aircraft has ever stalled on approach due to inappropriate speed additives? You put a lot of faith in software developers. Now I am an airline pilot, but I also develop software and work closely with developers far better than me, their mindset is very different from that of a pilot (as I know 'pilots'). In software features are added because they're <em>cool,</em> not because they're necessarily asked for or needed by the end user. Now this is my opinion, but modern planes are killing the skill of being a pilot. I am talking fundamental skills. Do modern pilots understand they need added back pressure on the yoke/stick when entering a bank? Do they understand you need to trim in the aircraft in pitch whenever speed changes?
I know this thread is about GSmini, but I couldn't help myself responding to your glorification of Airbus designers and engineers. Granted, they're top line in what they're doing. Doesn't necessarily mean their system is the only way that works. I am more worried about the disconnect between pilots and the air, come future.

I will try to explain my reasoning.

Firstly, my flying CV includes single and multi engine piston; Manual very basic turbo-props. Semi-automatic turbo-props, basic manual jets, semi-automatic Jets, and Airbus FBW.

Trimming is of course required owing to the lift equation, where changes in air speed results in changes of lift, and which therefore require changes in the THS or elevators to maintain level flight. Since the very beginning, this has always bugged me - as an engineer - as to why pitch trimming had not been designed-out. Along came Airbus, and they did just that - brilliant !

It is obvious to me that Airbus in their early days must have purchased a B737 and flown and evaluated it. After extensive flight testing, they must have said, "this is very good, but with modern technology and electronics, we can improve it further" which they did.

Many 'conventional' pilots in my experience, do not understand the Airbus FBW, and some pilots have difficulty with the FBW - hence some horrendous crashes. I have witnessed pilots in the other seat shouting "don't fight me", when the FBW was actually assisting them, if they would only relax and let it help them. I have had to explain - with diagrams - to former Boeing pilots how the Airbus GS Mini system works, (opposite to the Boeing system).

172_driver
8th Aug 2023, 06:57
I will try to explain my reasoning.

Trimming is of course required owing to the lift equation, where changes in air speed results in changes of lift, and which therefore require changes in the THS or elevators to maintain level flight. Since the very beginning, this has always bugged me - as an engineer - as to why pitch trimming had not been designed-out. Along came Airbus, and they did just that - brilliant !


You are of course entitled to your opinion. My CV is years of instructing private, instrument, multi-engine. 12 years on the 737 and shortly moving to the A320. I might be surprised how good it is! The only thing my colleagues have sold me so far is the table :p

vilas
8th Aug 2023, 12:22
I think the discussion is not taking all factors in consideration together. GSmini is Airbus way of handling change/variation of wind speed on approach. It deals with real time gust. It requires two things, activation to approach phase and managed speed. First is always done. Second has a possibility of going select speed but without GSmini. Now let's say you were flying a Boeing or A310 VLS 135kt and surface wind 20kt gusting to 30kt. So you will be flying Vapp of 155kts(10+10). You can' only accept speed restriction to fly beyond 155kts. It doesn't deal with actual gust on approach but at surface. So if you don't want to use GS mini then 155kts is minimum you can fly and not below. With the non Airbus way you could be flying the high Vapp correction even without aircraft facing that gust aloft. If at threshold the gust is not there then touchdown will be at higher speed because gust correction needs to be maintained. While GSmini will try to reduce the speed to Vapp on it's own. Yes! Conventional method is still used but can not be considered smarter. GSmini is new realistic way of dealing with actual winds faced all the way down. Since Neos deceleration is less so they only use 33% of wind experienced to arrive at the threshold at lesser speed.

CVividasku
8th Aug 2023, 13:08
The conventional airbus way of managing wind is one third of the total wind (limited between 5 and 15kt), so 145kt in your example.

Uplinker
11th Aug 2023, 11:36
My apologies for not being aware of the K factor for GS Mini, (= 1 for A320 classic and A330, that I fly, but only 0.33 for the Neo). I am now

Hi, 172: I am sure that you will love the Airbus FBW ! At least, I hope you will. I went onto it from BAe 146, and took to it like a duck to water. After about 12 years, I flew the B737 Classic for a year, and - sorry, no offence - but I hated it compared to the Airbus, ! (I found the B737 easy to fly, although I found its automation a bit patchy and random) :)

Apart from the table (!), the Airbus FBW has an unobstructed view of the instruments, and everything, including the overhead panel, is much more logically laid out, just to mention a couple of advantages.

FWIW; it took a while to get through my skull that the Airbus FBW will "stay where you put it", i.e. after you return the side-stick to neutral, it holds the last attitude you commanded, (within reason, certain rules, and weather allowing - and without any trimming by you. It is fantastic ! ). When I realised this, I stopped over-controlling and my manual flying improved a lot.

hans brinker
12th Aug 2023, 03:17
GS mini is not for gusts. It does what the name says: ground speed minimal. Simplified: It takes your current headwind component, checks it against the head wind component for the runway based on the wind on the perf page, and adds the difference to Vapp. If the difference is negative, it doesn't subtract, to not go below Vapp. This will keep your ground speed and kinetic energy relatively constant.
Suppose the ground winds are calm, the headwind on the approach is 30kts until 200', Final approach speed is 140kts. In product B, you would be flying 140kts IAS, and have 110kts GS. Passing 200' you would still have 110 kts GS, and your airspeed would be decreasing towards 80kts IAS, with a huge power increase required. Not a good situation, so Airbus decided to introduce GS mini. Difference between headwinds aloft on the approach and on the ground is 30kts, Vapp is 140 kts, so bug at 170 kts (yeah, on the 320, can be pretty close to 177, I have seen that). As you pass through the change in wind, GS stays 140, the IAS changes from 170 to 140, no huge power increase required, and everything is great.
Is it perfect? No, but is a lot better than not having it. The higher approach speed means higher power, and as you enter the shift to less headwind that can lead to the speed increasing before the AT reacts, so probably less than 100% HC would be enough.......

hans brinker
12th Aug 2023, 03:28
I will try to explain my reasoning.

Firstly, my flying CV includes single and multi engine piston; Manual very basic turbo-props. Semi-automatic turbo-props, basic manual jets, semi-automatic Jets, and Airbus FBW.

Trimming is of course required owing to the lift equation, where changes in air speed results in changes of lift, and which therefore require changes in the THS or elevators to maintain level flight. Since the very beginning, this has always bugged me - as an engineer - as to why pitch trimming had not been designed-out. Along came Airbus, and they did just that - brilliant !

It is obvious to me that Airbus in their early days must have purchased a B737 and flown and evaluated it. After extensive flight testing, they must have said, "this is very good, but with modern technology and electronics, we can improve it further" which they did.

Many 'conventional' pilots in my experience, do not understand the Airbus FBW, and some pilots have difficulty with the FBW - hence some horrendous crashes. I have witnessed pilots in the other seat shouting "don't fight me", when the FBW was actually assisting them, if they would only relax and let it help them. I have had to explain - with diagrams - to former Boeing pilots how the Airbus GS Mini system works, (opposite to the Boeing system).

What baffles me is the decision to not have any aileron trim, rudder trim in manual flight only, and pitch trim setting required to do manual before take off, but not used in flight (emergencies excluded).
With the rudder they could have taken the same approach as with the THS: after a consistent input of the pilot, start to trim it out.
With the THS, after I put in the M/B data in the FMS, it could set the THS for me (It resets to 0 automatically after landing after all).
I am not saying they were wrong, I just haven't found the answer to why...

J.L.Seagull
12th Aug 2023, 09:22
GS mini is not for gusts. It does what the name says: ground speed minimal. Simplified: It takes your current headwind component, checks it against the head wind component for the runway based on the wind on the perf page, and adds the difference to Vapp. If the difference is negative, it doesn't subtract, to not go below Vapp. This will keep your ground speed and kinetic energy relatively constant.
Suppose the ground winds are calm, the headwind on the approach is 30kts until 200', Final approach speed is 140kts. In product B, you would be flying 140kts IAS, and have 110kts GS. Passing 200' you would still have 110 kts GS, and your airspeed would be decreasing towards 80kts IAS, with a huge power increase required. Not a good situation, so Airbus decided to introduce GS mini. Difference between headwinds aloft on the approach and on the ground is 30kts, Vapp is 140 kts, so bug at 170 kts (yeah, on the 320, can be pretty close to 177, I have seen that). As you pass through the change in wind, GS stays 140, the IAS changes from 170 to 140, no huge power increase required, and everything is great.
Is it perfect? No, but is a lot better than not having it. The higher approach speed means higher power, and as you enter the shift to less headwind that can lead to the speed increasing before the AT reacts, so probably less than 100% HC would be enough.......

Finally, someone gets it and concurs with what I posted earlier. It's about the difference in surface and aloft winds, for the reasons mentioned already.

nothing to do with transient gusts.

Uplinker
12th Aug 2023, 11:43
My copy of 'Airbus Industrie A320 Family Instructor support' 2001 states on page 68:


The GS mini guidance has 3 major benefits:

1. It allows an efficient management of the thrust in gusts or longitudinal shears. Thrust varies in the right sense but in a smaller range(+/- 15% N1) in gusty situations which explains why it is recommended in such situations.

2. It provides additional but rational safety margins in shears.

3. It allows pilots "to understand what is going on" in perturbed approaches by monitoring the target speed magenta bugs: when it goes up = head wind gust.



(all punctuation and bold is Airbus').

Then there follows an explanitory diagram, and the text below that states:


........We can notice that in between a) and b) we have a front [20 kt] gust. We shall see on the PFD speed scale the target speed going up from 137 kts to 157 kts, while simultaneously the speed trend arrow and the IAS will go up for obvious aerodynamic consequences; the thrust will increase, but not excessively because of the speed trend already experienced.



And finally a diagram showing the PFD speed scale annotated with:


Head wind gust
IAS and speed trend arrow go up, target speed goes up and N1 smoothly increases

(Airbus' bold again, but all quotes hand typed by me)

Uplinker
12th Aug 2023, 11:48
I would post a photo of the page, but I don't think that would be allowed for copyright reasons?

CVividasku
12th Aug 2023, 17:26
What baffles me is the decision to not have any aileron trim, rudder trim in manual flight only, and pitch trim setting required to do manual before take off, but not used in flight (emergencies excluded).
With the rudder they could have taken the same approach as with the THS: after a consistent input of the pilot, start to trim it out.
With the THS, after I put in the M/B data in the FMS, it could set the THS for me (It resets to 0 automatically after landing after all).
I am not saying they were wrong, I just haven't found the answer to why...
That sounds like a very bad idea.
Which only shows that the same idea on the longitudinal axis is debatable to say the least.

hans brinker
12th Aug 2023, 20:56
That sounds like a very bad idea.
Which only shows that the same idea on the longitudinal axis is debatable to say the least.

Could you clarify what part of what I posted would be bad. Because that is exactly what both boeing and airbus do currently. And I have flown with aircraft that do that in the longitudinal axis.

hans brinker
12th Aug 2023, 21:04
My copy of 'Airbus Industrie A320 Family Instructor support' 2001 states on page 68:

Quote:
The GS mini guidance has 3 major benefits:

1. It allows an efficient management of the thrust in gusts or longitudinal shears. Thrust varies in the right sense but in a smaller range(+/- 15% N1) in gusty situations which explains why it is recommended in such situations.

2. It provides additional but rational safety margins in shears.

3. It allows pilots "to understand what is going on" in perturbed approaches by monitoring the target speed magenta bugs: when it goes up = head wind gust.
(all punctuation and bold is Airbus').

Then there follows an explanitory diagram, and the text below that states:

Quote:
........We can notice that in between a) and b) we have a front [20 kt] gust. We shall see on the PFD speed scale the target speed going up from 137 kts to 157 kts, while simultaneously the speed trend arrow and the IAS will go up for obvious aerodynamic consequences; the thrust will increase, but not excessively because of the speed trend already experienced.
And finally a diagram showing the PFD speed scale annotated with:

Quote:
Head wind gust
IAS and speed trend arrow go up, target speed goes up and N1 smoothly increases
(Airbus' bold again, but all quotes hand typed by me)

I would love a copy of that manual.

And that doesn't really contradict what I said/meant. I was talking about GSmini not being designed for gusts conditions in the flare. Your manual is talking about gusts and shears encountered while on the approach, the same position as I was talking about when I said headwind component while on the approach.

CVividasku
12th Aug 2023, 21:57
Could you clarify what part of what I posted would be bad. Because that is exactly what both boeing and airbus do currently. And I have flown with aircraft that do that in the longitudinal axis.
The part that I put in bold.
An automatic rudder trim input.

hans brinker
13th Aug 2023, 01:57
The part that I put in bold.
An automatic rudder trim input.

So why would that be a bad idea? And why isn't it a bad idea to do the exact same thing with elevator trim?

I guess you think in case of an engine failure people use the rudder input to see what engine failed. But there have been plenty of engine failures where the pilots shut down the wrong engine. And the pilot not flying should always confirm what engine is failed. Guess what he uses....
The Cessna CJ uses bleed differential to add rudder bias for an engine failure, so when you have an engine failure you step deeper into the pedal on the working engine side. Takes 10 minutes in the SIM to get used to, and same to get unused to.

sonicbum
13th Aug 2023, 08:51
What baffles me is the decision to not have any aileron trim, rudder trim in manual flight only, and pitch trim setting required to do manual before take off, but not used in flight (emergencies excluded).
With the rudder they could have taken the same approach as with the THS: after a consistent input of the pilot, start to trim it out.
With the THS, after I put in the M/B data in the FMS, it could set the THS for me (It resets to 0 automatically after landing after all).
I am not saying they were wrong, I just haven't found the answer to why...

From the A330 onwards the THS is automatically set after start when all hydraulics are available.

Why would you need aileron trim? Why would you need the rudder trim with AP ON?

As for the engine failure, the PM will announce ďEngine FailureĒ without specifying the engine; this in order not to confuse the PF and induce errors. The good old ďkick the ballĒ always works, the ďballĒ is blue and is called the Beta Target. Thatís all you need really.

Uplinker
13th Aug 2023, 11:59
:) GS mini is not for gusts.


Airbus Industrie:


The GS mini guidance has 3 major benefits:


1. It allows an efficient management of the thrust in gusts or longitudinal shears. Thrust varies in the right sense but in a smaller range(+/- 15% N1) in gusty situations which explains why it is recommended in such situations.........



(my bold this time).


I am not really having a go; just couldn't resist :)



What baffles me is the decision to not have any aileron trim, rudder trim in manual flight only, and pitch trim setting required to do manual before take off, but not used in flight (emergencies excluded)....



I have never really understood the desire to retain manual trimming. If it can be designed-out, why would you still want to trim manually?


It is like if motorists said they wanted to keep manual chokes, rather than have the car engine management control unit do it automatically. Or preferring the early gas turbine engines without ECUs or FADECS, which needed a flight engineer to look after them.


I flew many manually trimmed aircraft before Airbus FBW, (and flew them well enough, though I say so myself), but the Airbus auto-trim was a revelation. It just stays in the attitude you put it, (within certain limitations and caveats). Brilliant.



I cannot remember where I got my copy of The A320 Instructor Support manual. Airbus Industrie, ref: UGH01041, dated 2001.

https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/1280x960/ed073c30_5581_4a7d_9022_78267546bb52_56d7cfda0193519a5e20cea 13e35e9ef071bdf6a.jpeg

J.L.Seagull
13th Aug 2023, 15:37
So why would that be a bad idea? And why isn't it a bad idea to do the exact same thing with elevator trim?

I guess you think in case of an engine failure people use the rudder input to see what engine failed. But there have been plenty of engine failures where the pilots shut down the wrong engine. And the pilot not flying should always confirm what engine is failed. Guess what he uses....
The Cessna CJ uses bleed differential to add rudder bias for an engine failure, so when you have an engine failure you step deeper into the pedal on the working engine slide. Takes 10 minutes in the SIM to get used to, and same to get unused to.

Boeing already has that on the 777 and 787. It's called TAC (Thrust Asymmetry Compensation)..

Airbus doesn't have manual aileron trim because in normal law, it does it automatically (to some extent) when an engine fails

hans brinker
13th Aug 2023, 17:06
From the A330 onwards the THS is automatically set after start when all hydraulics are available.

Why would you need aileron trim? Why would you need the rudder trim with AP ON?

As for the engine failure, the PM will announce “Engine Failure” without specifying the engine; this in order not to confuse the PF and induce errors. The good old “kick the ball” always works, the “ball” is blue and is called the Beta Target. That’s all you need really.

I think you might have misunderstood what I was trying to say. I don't want aileron trim, and I don't want rudder trim AP on. I was trying to say that I do not want rudder trim AP OFF.
And thank you for the A330 THS info, did not know that. Will probably appear on the 320 at some point, but could have been there from the start.

And I know the how to fly the 320, and how the Beta target works. My question is, if the plane knows exactly where the rudder should be to center the Beta target, why doesn't it set the rudder there? The whole airbus philosophy of manual flight is that if you don't touch anything nothing will happen/change. Having to stand on the rudder to go straight and manually trim the force out in normal law really contradicts that philosophy IMO. The least they should have done was to have the rudder trim the force out automatically as the pilots keeps the Beta target centered, and the real Airbus way would be that the rudder would be trimmed towards Beta target centered even without rudder input by the pilot, just like it does AP ON. It handles aileron and THS that way, both AP ON or OFF, why not the rudder? Just my opinion.

hans brinker
13th Aug 2023, 17:22
Boeing already has that on the 777 and 787. It's called TAC (Thrust Asymmetry Compensation)..

Airbus doesn't have manual aileron trim because in normal law, it does it automatically (to some extent) when an engine fails

TIL about B being better than A ;) . And yes, I know why A doesn't have aileron trim, I just feel we shouldn't need rudder trim in normal law either.

hans brinker
13th Aug 2023, 17:28
:)
I am not really having a go; just couldn't resist :)

I have never really understood the desire to retain manual trimming. If it can be designed-out, why would you still want to trim manually?

It is like if motorists said they wanted to keep manual chokes, rather than have the car engine management control unit do it automatically. Or preferring the early gas turbine engines without ECUs or FADECS, which needed a flight engineer to look after them.

I flew many manually trimmed aircraft before Airbus FBW, (and flew them well enough, though I say so myself), but the Airbus auto-trim was a revelation. It just stays in the attitude you put it, (within certain limitations and caveats). Brilliant.

I cannot remember where I got my copy of The A320 Instructor Support manual. Airbus Industrie, ref: UGH01041, dated 2001.


LOL on the gust reference :) . Technically correct!! A320 is my 5th type, and I love the plane, just always somethings could be better....
And I think I found your manual online, will definitely read it!

vilas
14th Aug 2023, 06:40
The whole airbus philosophy of manual flight is that if you don't touch anything nothing will happen/change.
As long as nothing fails. Engine failure is managed by yaw damper but has limited authority so remaining work pilot has to do. If something fails and aircraft goes in alternate law, pitch(rather 1g flight path) will be managed but roll pilot will have to look after. Airbus is going for more and more automation in A350. A320 is the first came in 88 so will not have everything later versions have.

Uplinker
14th Aug 2023, 09:47
Yes, It was explained to me that although the A320 family FBW could put in all the rudder required, it is only programmed to put in about half so that PF has to put in the rest and is therefore aware of the engine failure, and more to the point, WHICH engine has failed. i.e, it keeps PF involved in the control of the aircraft and what is going on.

This helps maintain the piloting skill and prevents 'rusting'.