Few basic questions about A320

[mfclearner]

1. I want to know what is significance of activating approach on A320 FMGC? What would happen if I commence approach without activating.
2. What is ground speed mini in layman's language?
3. Is there any limitation of speed break extension with Flap position and landing gear extended?
4. What exactly is different in case of Auto Start and Manual Start?
5. Why are there Starter duty limits? What's basic mechanism imposing starter duty limits?

[FlyingStone]

1. Managed speed will still be 250 kts or any lower speed constraint in the FMGC route, but will not go to the approach speed. You can still fly the approach the "old way" - selected speed.

2. Energy compensation system to ensure engines are not at idle thrust during approach. (This is a very simple explanation.)

3. No, except that speedbrake is inhibited in CONF FULL.

4. Auto start = auto. Manual = you are responsible for fuel & ignition and you have less protections.

5. Starter has to turn the entire N2 shaft, so there is quite a lot of load on it. On top of that, it does that by getting a supply of very hot air from the pneumatic system. And there is no need of putting starters on the aircraft that can run for hours without cooling.

[Feather44]

2. Mostly designed to keep the aircraft out of shear.

[Contact Approach]

2. designed to confuse and scare the c**p out of you.

[Lantirn]

2. Designed to land with idle thrust and do hard landings 😂

[Chris Scott]

Quotes re GS-MINI:
"2. designed to confuse and scare the c**p out of you."
"2. Designed to land with idle thrust and do hard landings."

Not sure which member of the A320 you two are referring to and there's always a possibility that things could have been changed in the last 15 years (!), but in my day on A320 (CFM) and A319 (IAE) the GS MINI worked a treat - with or without A/THR.

In manual thrust, you must treat the IAS target as a target speed, NOT a minimum speed. Which, of course, is what the A/THR should be doing. But I doubt many of you are even allowed to fly approaches with manual thrust? (Except, of course, when it fails or perhaps when you have an engine failure? :ugh: )

GS-MINI is a great way of managing energy on an approach. Some of us used to calculate the estimated threshold GS on previous types with an INS ground-speed indicator, and vary the selected IAS to avoid ever going slower. On the A320, the system does that for you. Don't be tempted to enter a higher wind than expected into the PERF page, because - although that will give you a higher Vapp - it will unfortunately permit a lower minimum GS than is safe. So a lot of thrust is likely to be needed to regain Vapp when crossing the threshold to avoid that hard landing.

In practice the thrust settings remain much steadier with GS-MINI than with selected IAS. A light A319 may use a low thrust setting throughout, but that's going to happen anyway.

A slight complication arises when ATC demands a speed of (say) 160 until (say) 3 miles. In a strong headwind, the resulting GS may be well below the GS-MINI. When changing from selected IAS to managed IAS when there's still a strong headwind, the GS-MINI may cause the IAS target to shoot up above the Flaps Full limiting speed.

The trick is for the PF to know what the GS-MINI is. Note the Vapp displayed on the PERF page, approximate what that represents as a TAS (if, say, you are at a high altitude airfield), and subtract the headwind component of the entered W/V from the TAS to get the GS-MINI.

At 3 miles (in this example), if the actual GS is still lower than GS-MINI, maintain your selected IAS (160 in this example) until the actual GS rises close to the GS-MINI. Then select managed speed and continue as normal, following the target IAS.

Simples! :cool:

[Lantirn]

Chris Scott, it was a joke. But I will tell you my story.

GSmini is a great function, everyone who flies Airbus knows it well. It can save your day if you enter inadvertently microburst conditions.

I know I will piss off some "fully managed" pilots.

But it really happened to me once! A321 heavy GW, gusty, IAS target fluctuated a lot as the wind was changing and was bumpy. As I crossed about 40 feet the wind decreased due to gust, IAS target dropped, however very low thrust was commanded with an (already) reduced thrust and then suddenly I encountered a downdraught. No options at all, you just can't pull at that stage. You land hard or you hit the tail. Went around and it was a very positive touch even with the takeoff thrust.

We fly everyday at places where turbulent local wind phenomena prevail with low winds (someplaces only 15 knots wind limit), of course with arc wind limits. This airport was not even one of those cases, but I have seen a lot about how GSmini behaves and I can assure you, it's not designed for such conditions. I have seen many people going first time in such places insisting to fly managed speed and it's funny. Because you tell them but they trust her blindly.
-"You were right..."
-"I told you"
😂

By the way: By 50 feet it is supposed to remove all the tower wind addition so IAS target will reduce. With a lot of wind, this simply don't happens and the entered winds were correct, confirmed by ND, many times. A 15 year old kid can understand that 10 knots of a sustained gust cannot be removed by only 50 feet, but, the problem is IAS target stays there, high and hot. It is not supposed to work like this according to books.

It's not my intention to convince anyone. These are personal opinions which are based in personal experiences. That's mine. Don't take it wrong and I always fly speed managed in approach. But when things are really gusty without TS or CBs around and from the wind arc direction, I go selected. Some in the fleet add some knots more in managed in conf full(about Vls+10). Others go conf3 Vls+15. Others go ATHR off but I don't like it, too much workload. But you have to keep some space from Vls or you will regret it. Local phenomena can be anticipated when you know the place.

I love Airbus and I'm not a former 737 pilot, but 737s fly thousand of approaches "selected" every day. Come on. Selected is an option, it is allowed, sometimes it is better, sometimes not. Too much debate. It's like flying in managed DES when you know that you will not fly the whole arrival, transition, whatever.

About your comment about manual flying: Our company encourages to fly with automation off in VMC and familiar airports. I fly regularly FDs OFF takeoffs, raw data approaches, including autothrust off.

Many MSNs in the fleet, including 319s, 320s, 321s all IAE. Also CEOs.
Maybe CFMs are better, I actually have heard something about.

Fly safe!

[Contact Approach]

Quotes re GS-MINI:
"2. designed to confuse and scare the c**p out of you."

A slight complication arises when ATC demands a speed of (say) 160 until (say) 3 miles. In a strong headwind, the resulting GS may be well below the GS-MINI. When changing from selected IAS to managed IAS when there's still a strong headwind, the GS-MINI may cause the IAS target to shoot up above the Flaps Full limiting speed.

This be the ticket - that devilishly-dynamic thing we call wind. Sounds somewhat contradictory...

[vilas]

Lantirn
I haven't understood the point you are trying to make.
But it really happened to me once! A321 heavy GW, gusty, IAS target fluctuated a lot as the wind was changing and was bumpy. As I crossed about 40 feet the wind decreased due to gust, IAS target dropped, however very low thrust was commanded with an (already) reduced thrust and then suddenly I encountered a downdraught. No options at all, you just can't pull at that stage. You land hard or you hit the tail. Went around and it was a very positive touch even with the takeoff thrust.
This is not an example of limitation of GS mini but rather an example of any aircraft controllability against dynamic environment. Flying even in select speed or with fixed addition like in Boeing way would also result in a GA. With GS mini you arrive at the threshold at a predetermined ground speed and your landing performance is determined by that ground speed and not IAS. Also flare and touch down depends on IAS not on thrust. So if your speed is high you could be landing with idle thrust.

[vilas]

Chris
A slight complication arises when ATC demands a speed of (say) 160 until (say) 3 miles. you are supposed to be stable by 3nm(1000ft) which includes proper thrust. If ATC asks you that the answer is "Unable". Another way of looking at it. You are in a Boeing and you are flying wind+gust approach speed would you accept ATC speed limit to fly below that speed? Any way GS mini MAX speed is limited to VFE-5 for full flap configuration.

[Uplinker]

If you are stable on approach and the headwind or a gust increases airspeed; Airbus G/S mini increases thrust to maintain the same groundspeed as before*. Other types decrease thrust in that situation to maintain the same airspeed.

When the gust disappears, the Airbus engines are spooled up, and it has the same energy and groundspeed as before. Other types' engines are spooled down, so their aircraft has less energy until their engines spool up again.

*G/S mini = Ground speed minimum.

[Lantirn]

We are getting off topic sorry!

Vilas you are correct about the groundspeed but your lift depends on your IAS during the flare. The point is that in decreasing headwind IAS target drops.

Will show you what I mean, imagine this.

Wind Effect
Managed-Thrust
(Selected-Thrust)

1)
Headwind increases +10 knots and is almost constant until 100ft.
IAS target increases-Thrust increases
(IAS increases-Thrust decreases)

2)
Headwind decreases suddenly -5 knots at 60ft.
IAS target decreases-Thrust decreases
(IAS decreases-Thrust increases)

3)
Headwind decreases more now, -5 knots at about normal flare height.
IAS target decreases more-Thrust decreases more
(IAS decreases more-Thrust increases more)

Now you have a normal downdraught, not something special. Engines are at a low N1 with managed speed. You have to go around and if high GW the possibilities of touching the runway hard before the positive climb are very high. (Or you arrest the sink rate and you scratch your tail)

Same scenario speed selected, the thrust is increased every time the headwind decreases and the lift is enough for a go around, even for a landing because engines accommodate very quickly the loss of speed. Plus they are spooled up ready for a GA. You can not flare with idle thrust in such conditions, one day you will hurt a lot the landing gear.

I don't say that it is a limitation of GSmini. But it is more likely that with GSmini you will have to go around or be lucky until the conditions get better to land. That's why they say "approach can be flown in managed or selected speed".

Another point is the lag that happens during computations of GSmini. It can't calculate quickly and that's really annoying. It adds speed after a while and the engines spool when the wind now is reduced. This contributes more to a unstabilised approach during later stages of the approach. It's expected since it has to do its calculations. But this is like a self-oscillation.

But you have to see this happening. In theory everything works perfect!

It's personal opinion. I'm not trying to say that gsmini is useless. Actually I like it a lot.

[Chris Scott]

Hi vilas,

You are quite right: I would also reject that particular one. Your stabilised-approach criteria are evidently the same as ours were, so - in my (random) example of a 160 knots ATC restriction until 3 miles - simply amend that distance to 4 miles. I think you'll agree that the latter is very common. It certainly used to be at busy European airports, and I doubt much has changed.

Do you use the tactic I described to avoid the risk of exceeding the flaps limiting speed?

One of the problems our GS-mini used to create for ATC on windy days in the early years of A320 operation was that, in those last 4 miles, we would start to catch up with the preceding B737 or B757. The reasons for that were twofold:
(1) at an average weight our Vapps were higher than those of the Boeings;
(2) on very windy days, once released from the ATC speed restriction, the Boeings flying selected speeds would (of course) allow their GS to fall well below what it needed to be later at the threshold. The A320, on the other hand, flies a more-or-less constant GS all the way in.

Hi Lantirn,

Your newly-thoughtful response is much appreciated! Perhaps I should explain that I did 17 years on 5 different big jets before finishing my career with 14 years on the A320 and A319. Cannot claim to have experience of the most hazardous airfields in the world, but flying an approach at high weight into the short runway at Jersey, for example, on a very windy night is a pretty good test of the GS-mini.

You seem to be arguing that GS-mini works well in light-to-moderate windsheer conditions, but that you would not trust it when the going gets really tough? And certainly not on the tailstrike-prone A321? In which case, you are disabling it in the very conditions it is designed to protect you from.

You will agree that a tailstrike is much more likely to occur if the IAS drops below Vapp. Properly used, GS-mini is the best protection against that happening as a result of a sudden loss of headwind. As vilas says, extreme conditions, such as sudden downdrafts, may exceed the capability of any aircraft to perform a safe landing, in which case a go-around is the only safe course.

By advocating selected speed (presumably Vapp, unless you are adding random fat?), you are committing yourself in most cases to arriving at the threshold with a shortage of energy so that - when the headwind drops - the engines are forced to a higher thrust setting that you think will assist the flare. Well, that's how we had to do it in the bad old days!

The A320 is perfectly capable of being flared for a smooth touchdown (if that's what you want) from VLS at idle thrust. That might not be a good idea on the A321, because of the resulting pitch-angle. But to suggest that the vertical component of a lot of thrust is necessary to flare adequately would suggest that the aircraft's approach speeds were miscalculated during certification. That seems unlikely.

I do not recall experiencing the lag you describe in the reaction of the target IAS to changing headwind components. That would be unacceptable, so perhaps others will comment.

By the way, in my time on the A320/A319, Airbus recommended use of Flaps 3 in windsheer, but at pilot's discretion. I imagine that the A321 is even more susceptible to tailstrike using Flaps 3. What is the recommendation in your FCOM for the A321 in windsheer?

Good to hear that at least one airline is allowing pilots to practise their basic flying skills, including the use of manual thrust. As I've commented before on this forum, the A320 manual thrust, once established, is a joy to use and - on the approach - particularly if you are in managed speed!

[Chris Scott]

Quote from vilas:
"Any way GS mini MAX speed is limited to VFE-5 for full flap configuration."

Thanks, that's evidently a useful mod since I retired. However, increasing the IAS from 160 (in my earlier example) to VFE-5 (say, 172?) with a burst of thrust would not necessarily make for a stable approach. From an ATC point of view, it would also increase the likelihood of your catching up with an old-fashioned type flying selected speeds.

[vilas]

Lantirn
The 5kts and ten kts examples are too benign and I would not loose much sleep over it. Speed target (it is a target and not real speed) reduction towards Vapp is perfectly in order it is not low speed. ATHR will not allow below Vapp. In select speed and manual thrust it can drop below Vapp. GS mini is especially recommended in wind shear conditions so I do not agree with your conclusion. From sixty feet to 30ft is two seconds you are imagining so many things to justify your conclusion. Since speed is still above Vapp you can manage the slight down draft.

[vilas]

Chris
The A320 is perfectly capable of being flared for a smooth touchdown (if that's what you want) from VLS at idle thrust. That might not be a good idea on the A321, because of the resulting pitch-angle. But to suggest that the vertical component of a lot of thrust is necessary to flare adequately would suggest that the aircraft's approach speeds were miscalculated during certification. That seems unlikely. I fully agree with you. During flare and touch down the speed at which it is executed is important not the thrust. Especially when speed is above Vapp you do land from idle thrust.

[Lantirn]

Scott
Your newly-thoughtful response is much appreciated! Perhaps I should explain that I did 17 years on 5 different big jets before finishing my career with 14 years on the A320 and A319.

Thank you! First of all congratulations and respect to you!

Cannot claim to have experience of the most hazardous airfields in the world, but flying an approach at high weight into the short runway at Jersey, for example, on a very windy night is a pretty good test of the GS-mini.

I didnt say that they are the most hazardous in the world, but they have some wind phenomena which are assumed special threats.

You seem to be arguing that GS-mini works well in light-to-moderate windsheer conditions, but that you would not trust it when the going gets really tough? And certainly not on the tailstrike-prone A321? In which case, you are disabling it in the very conditions it is designed to protect you from.

Never wrote this. Of course you trust GSmini when you use it, otherwise why one should use something he wont trust. I said that in certain conditions, excluding CB's and TS in the area close by (no microburst danger), at specific airports that you have the know-how about the orographic effects of the winds, I wouldnt use it, except when you expect a strong headwind decrease along the lower levels of altitude, which is very predictable if you listen to the towerwind Vs actual winds at the approach. But I said this is my opinion based on my experiences and others that I respect in the company.
I say again, I go selected on specific only cases. My standard technique is with GSmini.

You will agree that a tailstrike is much more likely to occur if the IAS drops below Vapp. Properly used, GS-mini is the best protection against that happening as a result of a sudden loss of headwind.

Correct. But then the engines are at low N1, which I dont like in this special environment. Again my opinion!

As vilas says, extreme conditions, such as sudden downdrafts, may exceed the capability of any aircraft to perform a safe landing, in which case a go-around is the only safe course.

Very well said!

By advocating selected speed (presumably Vapp, unless you are adding random fat?), you are committing yourself in most cases to arriving at the threshold with a shortage of energy so that - when the headwind drops - the engines are forced to a higher thrust setting that you think will assist the flare. Well, that's how we had to do it in the bad old days!

Again very well said! Actually more than Vapp (VLS+5 at least in Conf Full, I would go VLS+7 in turbulent conditions and depending on weight). If you expect strong headwinds, of course one should use GSmini and I strongly agree! Its very nice compensated!
When the wind is reported variable with intensity of 15 knots (no CB, no TS, its just the winds from certain direction behind a hill), you can imagine what is happening there. Its not funny, even at 1000ft which is the last gate for wind check and go around its very, very turbulent. I have actually seen a lot of strange things there only with 5 knots variability! Not funny again!

The A320 is perfectly capable of being flared for a smooth touchdown (if that's what you want) from VLS at idle thrust. That might not be a good idea on the A321, because of the resulting pitch-angle. But to suggest that the vertical component of a lot of thrust is necessary to flare adequately would suggest that the aircraft's approach speeds were miscalculated during certification. That seems unlikely.


I totaly agree with you! I dont said anything like this and I dont really care about the smooth touchdown. Airbus explains that we have to ensure that all thrust levers are at idle detent at the latest at touchdown. Which is why I dont like to see "with-autothrust-flare-smooth-landing" guys jeopardizing remaining landing distance for a smooth touch.

I do not recall experiencing the lag you describe in the reaction of the target IAS to changing headwind components. That would be unacceptable, so perhaps others will comment.

Its there very noticeable. Which I dont really care when I am in a strong headwind. No big deal! Also noticeable with crosswind approaches, which is not supposed to affect IAS target. And you have to add some knots in Vapp!

By the way, in my time on the A320/A319, Airbus recommended use of Flaps 3 in windsheer, but at pilot's discretion. I imagine that the A321 is even more susceptible to tailstrike using Flaps 3. What is the recommendation in your FCOM for the A321 in windsheer?


Same! All configurations can be used. Generaly conf full has better capability in handling. Conf 3 has the disadvantages that the engines are at lower N1 during approach which makes the spool times greater during gusts and the speed more unstable, plus the AOA is higher and more gust affected.
Major advantage of conf3 is the energy due to higher speed and configuration, less drag giving you great go around performance and better windshear escape capability.
The 321 has different flaps, so in conf3 it is different (more degrees) than 320's, but I dont like it because the speeds are already too high for landing, unless it is required.

I go conf3 in strong headwinds. I prefer full in all other cases, except when practicing conf3's from time to time! :)

Good to hear that at least one airline is allowing pilots to practise their basic flying skills, including the use of manual thrust. As I've commented before on this forum, the A320 manual thrust, once established, is a joy to use and - on the approach - particularly if you are in managed speed!
Indeed, I love manual flight. I really enjoy!

Vilas,

The 5kts and ten kts examples are too benign and I would not loose much sleep over it. Speed target (it is a target and not real speed) reduction towards Vapp is perfectly in order it is not low speed. ATHR will not allow below Vapp. In select speed and manual thrust it can drop below Vapp.

This approach was very important for me and believe me, If my touch was above limits I would lose my sleep for real! I saw what happened and I think I learned. Maybe in a couple of years, I will have other opinions.

GS mini is especially recommended in wind shear conditions so I do not agree with your conclusion.

Fair enough. You dont have to. :)

From sixty feet to 30ft is two seconds you are imagining so many things to justify your conclusion. Since speed is still above Vapp you can manage the slight down draft.

I am not imagining, FDM analysis because I was interested in this approach with the FDM analyst is not imagination. I managed the downdraught, someone else might be unlucky another day.
Its not so simple. It depends on multiple factors including weight, density, descent rate and if the lady would like to flare this day.

Fly safe!

[FlightDetent]

this reads strange to me: 2) Headwind decreases suddenly -5 knots at 60ft.
IAS target decreases-Thrust decreases The loss of HW component brings a drop in IAS and similar reduction of Vtarget: thrust remains the same.

By 50 feet it is supposed to remove all the tower wind addition so IAS target will reduce. That's not how it works.

GSmini is a great function, everyone who flies Airbus knows it well. The second part of the sentece, ehm ... let's call it a difference of opinions here :)

True, it is not designed or capable of doing any magic in gusty and dynamically changing conditions. All it does is a simple additive function over the measured steady HW component and its changes.

[Lantirn]

FD,

Both statements true.

Something I dont remember correctly maybe. What I remember is the IAS target coming low with a very low N1.

For the GSmini you are right. I was told that excess speed is removed but I checked again, it seems you are right. 🤓

[Chris Scott]

Hi Lantirn,

On an approach, as you know, if the headwind suddenly drops by (say) 10 knots, the IAS will fall by a similar amount. But as Uplinker has succinctly pointed out, the beauty of GS-mini is that the target IAS will also fall by about 10 knots, because it is programmed to maintain the same ground-speed. So, as he says, there is no requirement to add thrust like you would when flying selected IAS.

(For the benefit of the OP, that is the GS it has calculated to be appropriate for the arrival at the runway threshold. It is the TAS equivalent to the Vapp, minus the headwind component of the W/V inserted by the crew on the PERF landing page. In the event of a temporary tailwind on the approach, it will never allow the target IAS to fall below Vapp.)

Maintaining a constant GS means the VS remains the same all the way down the glide-slope. With the exception of up-drafts or down-drafts, the only need for a change in thrust arises from the gradual reduction in IAS that usually (but not always) takes place during a headwind approach. That can happen quite suddenly in the last stages of the approach, particularly at night, which can result in a thrust that seems lower than desirable. However, IIRC, certification demands full flare capability at idle thrust from a height of 50 feet, starting at VLS. As for the go-around case, both CFM and IAE engines can accelerate even from flight-idle to TOGA in about 5 seconds.

Flying an approach in selected IAS increases the risk of the speed falling below VLS due to a sudden loss of headwind. That loss of energy has first to be recovered in the event of a go-around. GS-mini greatly reduces that risk, so a go-around (for whatever reason) gets off to a good start.

[Uplinker]

Pilots who have flown Boeing do not like Airbus GS mini until they get their heads around it. They are nervous when the Airbus GS mini takes power off with a decreasing headwind, because that is opposite to what the Boeing will do. I flew with an ex Boeing guy once who wanted to use selected speed "to avoid it taking power off" during a turbulent approach. I managed to talk him out of it, by pointing out that it could be dangerous to effectively disconnect the GS mini.

Airbus A/THR can seem lazy, but of course it cannot anticipate, and presumably does everything at 1g. As long as the GS and base energy is maintained all is good. Manual thrust can of course be used but you must still follow GS mini, which can be quite lively !

[Chris Scott]

Quote from Uplinker (my emphasis):
"Manual thrust can of course be used but you must still follow GS mini, which can be quite lively !"

On the contrary! I did the majority of visual approaches with manual thrust in all wind conditions. It was far easier than on previous types that lacked GS-mini. Very few power changes were needed to follow the target IAS, for the very reasons FlightDetent and I have explained above..

[vilas]

Airbus A/THR can seem lazy, but of course it cannot anticipate, and presumably does everything at 1g. ATHR has nothing to do with 1g. Flight control computers do that when stick free or pitching with AP ON. ATHR acts with rate of deceleration and acceleration.

[Uplinker]

Fair enough, I wasn't sure, hence 'presumably'.

The A330 A/THR seems particularly lazy (slow to react) to me.

[FlightDetent]

when the Airbus GS mini takes power off with a decreasing headwind Still does not compute for me.

HW decreases, IAS drops. Vtarget drops too, by the very same amount. Thrust remains the same.

[Chris Scott]

Hi Flight Detent,

(Apologies for mixing you and Uplinker up in my previous post, now amended.)

Quote:
"HW decreases, IAS drops. Vtarget drops too, by the very same amount. Thrust remains the same."

Yes. GS-mini commands a constant ground-speed until the flare, meaning a constant VS. Assuming no up or down drafts, thrust can remain the same during sudden changes of headwind, for the reasons stated.

However, I think what Uplinker may have in mind is a point that I made in a previous post. As the target IAS reduces, the thrust needed to sustain it in the medium term will slightly reduce. For example, you need more thrust to fly a steady 170 knots than a steady 140.

[FlightDetent]

Dawned on me just after I submitted the last post, but was too lazy to edit. I had skipped reading that previous one of yours, seeing it was address to someone else. Apologies, will try harder starting already tomorrow! :) G'nite and thanks.

[rogerg]

you need more thrust to fly a steady 170 knots than a steady 140.


Depends maybe, the same AC at 140 will need a higher angle of attack so maybe drag will be greater = more thrust

[Chris Scott]

Quote from rogerg:

"Depends maybe, the same AC at 140 will need a higher angle of attack so maybe drag will be greater = more thrust."

As 140 kt is a typical Vapp on an A320 at a fairly high weight, that would suggest that the a/c is flown routinely below its minimum drag speed for Flaps Full and L/G extended. Can't quote you any figures, but I can assure you that is not the case. Speed stability is the norm on aerodynamically-conventional types (which the A320 definitely is).

IIRC, the only Western airliner certificated to fly approaches on the "wrong" side of the drag curve was the slatless, flapless Concorde.

[Octane]

Speaking of flying the aircraft manually with all the automatics off, My brother (737 Captain) told me recently he does this quite often to "keep in practice", often to the surprise/ consternation of the FO. Brother is a little concerned that some of his colleagues have no interest/ confidence is doing same. Should that be concerning, is it unusual for a pilot to want to manually fly the aeroplane and is it a skill all should practice?

Thanks

Michael

[Jay Li]

I doubt about that because:
The IAS targets have 2 limits:
‐ VAPP as minimum value
‐ VFE-5 kt in CONF FULL, or VFE of the next configuration in CONF 1, 2 or 3 as the maximum
value. According to FCOM DSC22

So GS-MINI wouldn't make the target speed to shoot up the limitation of Vfe.

But I can't understand "The purpose of the ground speed mini function is to take advantage of the aircraft’s inertia when the wind conditions vary during the approach". I thing GS-MINI just enegy keeper, how can related to inertia?

[Chris Scott]

Welcome Jay Li !

Quotes:

"So GS-MINI wouldn't make the target speed to shoot up the limitation of Vfe."
You are right, according to vilas - who already corrected me. But, in my days on the A320 (1988 - 2001), it often did because the software modification to prevent that happening had not been introduced.

"But I can't understand 'The purpose of the ground speed mini function is to take advantage of the aircraft’s inertia when the wind conditions vary during the approach'. I think GS-MINI just energy keeper, how can [it be] related to inertia?"
I also disagree with the sentence you have quoted, so I very much hope I didn't write it! :} They are certainly not the same, although related. As you know, in Dynamics, inertia is simply the same as mass (M). Kinetic energy is 0.5 Mv^2. The velocity (v) is, in our case, the ground-speed.

On the approach GS-mini stops the ground-speed (and, therefore, the kinetic energy) falling below the value which will be needed when the aircraft crosses the runway threshold. So it's a safer way of managing energy than selected speed, where kinetic energy will have to be added - using a thrust increase - if and when the headwind reduces.

Using selected speed, if the loss of headwind is large and sudden, the IAS will temporarily fall below Vapp, and maybe even below VLS, before the added thrust has time to increase the ground-speed (and, therefore, the kinetic energy) to where it needs to be. The greater the mass (all-up weight) of the aircraft, the longer it will take for a given thrust increase to do the necessary work. If the loss of IAS happens at a very late stage of the approach, an undershoot and/or hard landing is the likely result - so of course a go-around may be necessary.