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.