Which brands have GS mini function ?
 

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

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.
• You Tube

Have you tried pulling the knob?

As far as I know, only FBW Airbus planes have that feature.

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.

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?

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

Do this. It’s not rocket science.

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.

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!

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.

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.

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.

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.

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.

Isn't there a specified approach speed to set for when not using GSmini? Honest question from outside looking in.

I would ignore managed speed in very strong headwinds when it takes me too close to the bricks. 5 knot buffer isn’t enough sometimes. I might select speed if ATC want something specific and I’m happy that the selected speed puts us comfortably in the middle of the envelope. Mostly I let GS mini do it’s thing, I think it’s great.

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.

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

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.

The FMS will display Vref and Vref+5. GSmini works on top of that. SOP is to use it, and you can’t 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.

Just once the condition that’s making use selected speed has gone. I don’t fly to places with much ATC speed control so I’ve never had to use selected because managed was too fast, that’s a hypothetical example of when I’d use it. As for getting close to the bricks, I’ve had occasion when a strong wind at 2000’ has had GS mini giving a high speed target. In this case I’d 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.

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.

​​​​​​​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.

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

All the other posts seem to imply that selecting (pulling) speed, turns it off?

I was unclear. You can’t turn it off in the sense that it’s 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.

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.

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.

​​

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!

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 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.

Quote:

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

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From Airbus A320/321 FCOM:
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:

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.

??? 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. There’s also the fact that GS mini has been nerfed somewhat in the NEO aircraft so the system is less “active” in those.

Ah. I don't know about the NEO, sadly.