GS mini versus VFE

[Citation2]

Gusty conditions does not mean that there is windshear. I conquer with Villas , indeed flaps full configuration provides more stability and a better handling in gusty conditions . Flaps 3 increases manoeuvrability , and If windshear is reported then CONF 3 is the recommended configuration by Airbus.

There is no recommended flaps configuration for gusty conditions.

[Citation2]

FCTM Adverse Weather:« Configuration FULL, or 3, can be used.

CONF FULL provides better handling capability in turbulent conditions, however, CONF 3 provides more energy and less drag. »

[vilas]

Originally Posted by Citation2

FCTM Adverse Weather:« Configuration FULL, or 3, can be used.

CONF FULL provides better handling capability in turbulent conditions, however, CONF 3 provides more energy and less drag. »

It has to do with gain modulation of flight controls. F3 is very sensitive so F full handles better. There was an accident in Hong kong due to flap jam and go around which explains this. Google it. But climb gradient is an issue for whatever reason then off course F3 is better.

[Chris Scott]

Quote from vilas:
"It has to do with gain modulation of flight controls. F3 is very sensitive so F full handles better."

Yes. I'm not going to show my ignorance of the current A320 FCOM regarding recommended flap settings in windshear (and I wonder if the A321 might be different). But, back in the last century , the apparent skittishness of the A320 and A319 with Flaps 3 on the approach was said to be something to do with the fact that Flaps 3 is also a take-off setting.

Using Flaps 3, as Unhooked advocates, raises the VFE by 7 knots,if memory serves. But the GS-mini will itself be 5 knots higher to reflect the higher Vref.

BTW, does anyone want to comment on my technique for avoiding VFE exceedance in on the approach in a strong, gusty headwind when the runway headwind is considerably lower?

[vilas]

Originally Posted by Chris Scott

Quote from vilas:
"It has to do with gain modulation of flight controls. F3 is very sensitive so F full handles better."

Yes. I'm not going to show my ignorance of the current A320 FCOM regarding recommended flap settings in windshear (and I wonder if the A321 might be different). But, back in the last century , the apparent skittishness of the A320 and A319 with Flaps 3 on the approach was said to be something to do with the fact that Flaps 3 is also a take-off setting.

Using Flaps 3, as Unhooked advocates, raises the VFE by 7 knots,if memory serves. But the GS-mini will itself be 5 knots higher to reflect the higher Vref.

BTW, does anyone want to comment on my technique for avoiding VFE exceedance in on the approach in a strong, gusty headwind when the runway headwind is considerably lower?

As per the FCOM I quoted, in approach with flaps full the GSmini limit is VFE177-5=172kts a margin of 5kts from VFE and in approach with flaps three the limit is VFE NEXT which is 177kts while the VFE flap3 is 185 i.e. margin of 8kts from VFE Conf3. So the extra protection from VFE offered in CONF3 is a mere 3kts as compared flaps full. If you consider the much less drag of flaps 3 it is easier to exceed VFE in 3 than in full. The comfort factor is only imaginary. There is no dispute about using FLAP3 in expected windsheer conditions or where better climb gradient is required.
citation 2 I used the word gusty conditions what I meant was turbulent conditions.
Last thing, instead using home made pickles why no one in all these years asked the manufacturer what his idea is about the matter?

[vilas]

The report concludes that the aircraft, on its first approach, encountered a gust of sufficient intensity to produce asymmetric movement of the flaps. The asymmetric movement caused the flaps to lock and generated a "FLAPS LOCKED" message on the EC AM. By selecting the FLAPS lever to Config 3 as directed to by the ECAM the lateral control law became sensitive when the flaps were locked in the Config FULL position (40°) and hence rendered the aircraft difficult to control in roll in turbulent conditions.

HongKong Dragon air accident in 1994. Where they had flaps jam at full and go around in lever3 and subsequent three more approaches with lever3 caused severe oscillations. Since then procedure was changed to do approach in full if flap jammed >3.

[jmmoric]

We had a long discussion with carriers about wind given by ATC, when it comes to velocity, so far it sits with:

We will provide the latest wind direction and velocity, icluding variations to velocity of 10 kt or more.

We will update the information of wind, if the velocity changes by 10 kt or more.

So with a wind of 230/19 kt, and a maximum of 28 kt, the maximum will not be given. Changes to the wind will be given when it gets up to 230/29 kt.... which effectively mean, you may get the 230/19kt, and may end up landing with 230/28-37kt without any updates.

The reasoning from carriers was, that this span is included in the calculated limitations of the aircraft.

[Chris Scott]

Originally Posted by jmmoric

We had a long discussion with carriers about wind given by ATC, when it comes to velocity, so far it sits with:

We will provide the latest wind direction and velocity, icluding variations to velocity of 10 kt or more.
We will update the information of wind, if the velocity changes by 10 kt or more.
So with a wind of 230/19 kt, and a maximum of 28 kt, the maximum will not be given. Changes to the wind will be given when it gets up to 230/29 kt.... which effectively mean, you may get the 230/19kt, and may end up landing with 230/28-37kt without any updates.
The reasoning from carriers was, that this span is included in the calculated limitations of the aircraft.

That's right, and as far as I can remember that protocol on the reporting of gusts in METARS has not changed in around fifty years. Reported wind speeds are, of course, mean speeds, unless annotated as gusts. As you imply, pilots should be aware that gusts less than 10 kt above the mean speed are simply not reported on METARS or ATIS, although they may be by ATC officers to individual aircraft on Tower frequencies. Similarly, be aware also that gusts can also be negative, i.e. the wind may drop temporarily and significantly below the reported mean wind. Again, a helpful Tower controller will warn aircraft of this.

As far as this discussion on GS-mini is concerned, the wind speed for insertion into the PERF page is always the mean wind speed. Inserting a gust speed would increase the Vapp by less than it would decrease GS-mini. That in turn would result in lower managed IAS readings throughout the approach.

[vilas]

As far as this discussion on GS-mini is concerned, the wind speed for insertion into the PERF page is always the mean wind speed. Inserting a gust speed would increase the Vapp by less than it would decrease GS-mini. That in turn would result in lower managed IAS readings throughout the approach

That is correct. If you put higher wind in PERF you reduce GSmini protection. But pilot can add to Vapp. Upto 15kts is permitted.

[Chris Scott]

Originally Posted by vilas

As per the FCOM I quoted, in approach with flaps full the GSmini limit is VFE177-5=172kts a margin of 5kts from VFE and in approach with flaps three the limit is VFE NEXT which is 177kts while the VFE flap3 is 185 i.e. margin of 8kts from VFE Conf3. So the extra protection from VFE offered in CONF3 is a mere 3kts as compared flaps full. If you consider the much less drag of flaps 3 it is easier to exceed VFE in 3 than in full. The comfort factor is only imaginary. There is no dispute about using FLAP3 in expected windsheer conditions or where better climb gradient is required.
citation 2 I used the word gusty conditions what I meant was turbulent conditions.
Last thing, instead using home made pickles why no one in all these years asked the manufacturer what his idea is about the matter?

Thanks for clarifying that, vilas.

One minor observation, if I may: I think it's important not to confuse GS-mini - i.e., the minimum ground-speed calculated for an approach by the GS-mini system - with the "managed" IAS it calculates to comply with that minimum GS (and therefore, by definition, the Vapp). One way of avoiding possible confusion may be to refer to the latter datum as "GS-mini IAS", and the former as "GS-mini ground-speed" or "GS-mini GS".

Once the wind and flap setting have been entered into the PERF page, the GS-mini GS will remain fixed. But the GS-mini (managed) IAS will fluctuate according to the headwind component.


I agree that Flaps 3 is unlikely to be much help in avoiding a temporary VFE exceedance in the common situation that Unhooked describes, although the figures suggest - as you say - it gives an improved margin of 3 kt.

For beginners, can we put some numbers to a typical, gusty approach scenario and compare the two configurations?
Whatever wind has been entered into the PERF page, the Vapp for Flaps 3 will always be 5 kt higher than for Flaps Full.
Accordingly, the fixed GS-mini ground-speed will be 5 kt higher with Flaps 3. The GS-mini IAS will also be 5 kt higher with Flaps 3, unless VFE considerations come into play.

Flaps 3 landing
Let's take a simple, sea-level/ISA example, perhaps at night, where the runway HWC (head-wind component) is 10 kt, and the FMGC has calculated a Flaps 3 Vapp of 140.
Therefore, GS-mini GS is 130.
At 4-miles final, with a selected IAS of 170 (previous ATC requirement), the flight crew select Flaps 3 and then push the speed knob to command managed IAS for final approach.
At that moment, the HWC is 50 kt.
The system therefore calculates a GS-mini IAS of 180, but limits it to 177 (the VFE Flaps Full).
As the IAS reaches 177, the HWC increases by 10 kt in a gust, causing an instantaneous rise of IAS to 187.
So the VFE Flaps 3 is momentarily exceeded by 2 kt.

Flaps Full landing
Now let's use the same wind conditions as above, so the FMGC has calculated a Flaps Full Vapp of 135.
Therefore, GS-mini GS is 125.
At 4-miles final, with a selected IAS of 170 (previous ATC requirement), the flight crew select Flaps 3 and then Flaps Full, and then push the speed knob to command managed IAS for final approach.
At that moment, the HWC is 50 kt.
The system therefore calculates a GS-mini IAS of 175, but limits it to 172 (VFE - 5).
As the IAS reaches 172, the HWC increases by 10 kt in a gust, causing an instantaneous rise of IAS to 182.
So the VFE Flaps Full is momentarily exceeded by 5 kt.

IMO, we can conclude that the extra margin from VFE of using Flaps 3 is indeed 3kt, but the aeroplane is slightly more "slippery" when the pilot wants to slow down.

[vilas]

IMO, we can conclude that the extra margin from VFE of using Flaps 3 is indeed 3kt, but the aeroplane is slightly more "slippery" when the pilot wants to slow down.

That is true. In flaps full it will be quicker to pull the speed back.

[dream747]

If the pilot decides to add say 5 knots to the calculated VAPP by the FMGC, and punches that speed into the FMGC, does it adversely affect (if any) the GS mini in any way? As the minimum approach target speed is already raised by 5 knots. Airbus says we can do this, but are they really any real benefits, considering GS mini handles changes in HWC quite well already.

[vilas]

dream747
Increasing Vapp doesn't affect GSmini. It only decreases the range between the Vapp and VFE-5 thereby decreasing the ATHR activity which is good in extremely gusty conditions. But entering fictitious higher surface wind will decrease GSmini protection and should not be done.

[pineteam]

After observation, I checked carefully the GS mini function during flight during windy conditions and the first time it was exactly how FlightDetent sais: The first 10kt of extra wind was disregarded. It was a 321 CEO with Sharklets.
But then on another flight and plane, all the excess wind was considered to compute the VAPP.
Can’t remember exactly which plane it was tho.
I will try to observe and take accurate notes next time.

[Uplinker]

See what your approach ground speed is on the ND as well, and if it varies.

[retired guy]

Originally Posted by vilas

FD
I have dealt with latest CAE and True Sim even they don't have options to set winds every few hundred feet on approach nor CAEs earlier five versions had. The oldest I have used I am sure Chris has used, it didn't have Airbus airfield but had Toulose. The wind aloft options are way above platform altitudes. However when you enter surface wind it creates a pattern of winds away from ground which differ in direction and speed that's all. But no way 50kts for 20kts surface winds.
​​​​​​

Hi Villas
On every CAE sim I have been on in recent years we could set surface wind and 1500 ft circuit wind very different to make it realistic for base training. Say RW 27. Set 300/15 for touchdown and 360/50 for 1500 ft. Which means that during the approach the wind backs anticlockwise/southerly as it does, and the windspeed reduces requiring constant power addition.
I am not talking base training here - just the ability to set winds pretty much as you desire. Not "every few hundred feet" of course but two low down reference points.

Cheers
R Guy

[vilas]

R guy
I will recheck next time in two weeks when I visit sims again and get back.

[Mohfadl320]

approach scenario with flap 3 and the question would be like what’s the min and max speed commanded by GS mini in terms of VAPP and VFE.

[vilas]

Originally Posted by Mohfadl320

approach scenario with flap 3 and the question would be like what’s the min and max speed commanded by GS mini in terms of VAPP and VFE.

It has been discussed before. MAX speed with flaps 1,2 and 3 it is VFE next. So with Flap3 it will be 177kts. Minimum speed is always Vapp.

[Mohfadl320]

Dear thank you

Originally Posted by vilas

It has been discussed before. MAX speed with flaps 1,2 and 3 it is VFE next. So with Flap3 it will be 177kts. Minimum speed is always Vapp.

thank you for the information