View Full Version : Atc and airbus ground speed mini
A320-200PILOT
8th May 2011, 11:08
How to atc app controllers deal with the airbus ground speed mini function, in gusty conditions when the bus is holding a ground speed as opposed to vapp indicated airspeed, like a conventional aircraft would.
regards
ATCO Two
8th May 2011, 12:04
At Terminal Control we can select both IAS and groundspeed as required, and we are constantly monitoring the radar for any catch up, so I don't see this as a particular issue.
At Terminal Control we can select both IAS and groundspeed as required, and we are constantly monitoring the radar for any catch up, so I don't see this as a particular issue.
You obviously don't do LL FIN!
It can and does compromise final approach spacing/wake turbulence separation.
The trouble is (from a FIN pov) you don't know exactly what the aircraft is going to do until it does it, it might have the effect of speeding up or slowing down relative to what the aircraft in front or behind is doing.
If FIN says IAS 160 to 4 and the aircraft automatics dictate something different as they want to fly relative to ground speed, then FIN should be absolved if there are any upsets.
If it causes the aircraft to increase speed inside 4 dme, as seems to be the case as well, then the subsequent missed approach shouldn't be down to FIN either.
It's when it's windy and we're trying to do the bare minimum spacing to keep the landing rate up that speed variations can be most apparent. The speed consistency that is required for minimum spacing isn't conducive to having an unknown variable thrown into the mix, though I of course appreciate the rationale/protection behind it.
HEATHROW DIRECTOR
8th May 2011, 17:19
"I'm breaking you off this approach. Turn left heading 180...." Problem solved.
"I'm breaking you off this approach. Turn left heading 180...." Problem solved.
And you will have exactly the same problem on the next approach :hmm:
kick the tires
8th May 2011, 18:35
Selected speed solves all the issues of G/S mini.
True, slected speed does solve the issue. However this defeats the whole point of having ground speed mini.
If it creates problems for ATC (and I am sure it will at times) than it is best if ATC takes it up with the operaters. At least that will lead to a common practice followed by (hopefully) nearly all Airbus operators and ATC know what they can expect.
However during the TRUCE days this hasn't been mentioned as being a problem, yet. At LGW we do 160Kts to 4 miles anyway and I have been told (by a controller) that what you do in the last 4 miles (within reason) doesn't make that much difference to them. But standing by to be corrected.:ok:
HEATHROW DIRECTOR
8th May 2011, 19:56
Obviously I don't know which particular Airbus is involved, but I worked thousands of Airbus types - A319, A320, A321, A340 on Heathrow Final Director and never experienced any problems. What has changed in recent years?
HD, nothing has changed in recent years. All the Airbusses (318, 319, 320, 321, 330, 340 and most likely 380) have a function called ground speed mini.
It maintains a groundspeed and not an indicated airspeed. If you would ask us to maintain 160kts to 4 DME than we select this speed and fly it, i.e. 160 indicated. At 4 miles we go back to managed speed and on a windy day the ground speed mini might demand an indicated airspeed of 170kts (sometimes more) so the aircraft speeds up.
In general as far as I understand it is not a real problem for controllers when we fly a selected speed to 4 DME and than go managed speed, even if this means that we increase speed for a little while.
Where it can be a problem is when the controller ask us to reduce to minimum approach speed. In that case the speed can be high (170kts+ on windy day) while other (non airbus) traffic in fornt of us does 130 -140 kts.
Sorry not the best in explaining things but I hope this helped.
Mike Rosewhich
8th May 2011, 20:26
Fly selected speed of 160 to 4. Then Manage the speed. If the aircraft accelerates at the point, then so be it, it will only be for a short while.
If the winds were that gusty it would cause a problem, I suspect the final spacing might be increased.
Thats the way we have always done it. However the thread starter asks if this causes problems for ATC.
ZOOKER
9th May 2011, 00:26
If FIN says 160kts to 4 DME and non-compliance is observed, file an SRG1602.
KKoran
9th May 2011, 02:23
What is the benefit of flying a set ground speed?
HEATHROW DIRECTOR
9th May 2011, 06:41
CEJM... Many thanks for that. As I said earlier, I do not recall any problems with Airbus aircraft or any more go-arounds with those types than with any other. I can see that increasing speed inside 4DME could cause a problem for the tower, especially if 2.5nm spacing is being employed. Still, all adds to the fun, eh!!
Zooker, read the thread, this isn't about non-compliance.
Spitoon
9th May 2011, 17:22
If the pilot chooses to operate his or her aircraft in ground speed mini - or any other function - in order to comply with the ATC clearance I see no problem. If the controller wants the aircraft to fly at a particular airspeed for separation purposes I would expect the pilot to fly at that airspeed. If no specific airspeed is required, ground speed mini function seems fine. Any variations in airspeed resulting from the use of this function is unlikely to cause ATC difficulty else a specific speed would have been mentioned.
What would cause me concern is to specify an airspeed only to find that the aircraft is set up to fly at a particular groundspeed - the two are different.
To answer the original question (although I am no longer operational), in my day if I had not applied any speed control I probably would not noticed the variation in speed caused by ground speed mini function and it wouldn't cause a problem because the sequence wasn't tight enough to apply speed control. I should stress that I did not work a high-density environment and so was not routinely aiming for 3 miles - no more and no less - between aircraft. As Roffa points out, even small variations in speed difficult to accommodate in a sequence when the pressure is continually on to pack the aircraft as tightly as possible and the controllers are good at doing so.
babotika
9th May 2011, 19:20
What is the benefit of flying a set ground speed?
GS mini doesn't fly a set groundspeed, the function ensures that the total energy of the aircraft is maintained throughout the approach.
In plain english the actual GS won't ever decrease below the planned landing GS (VAPP-wind) so that if there was a sudden decrease in wind you wouldn't find yourself falling out of the sky.
The disadvantage is that the actual VAPP can be very high initially, and it can jump around if the wind is gusting.
S.
A320-200PILOT
9th May 2011, 22:56
wow thanks for all your replies. i knew this could be an issue, but, as one of the posters said if we are told to just reduce to min app speed, and not allocated a speed, then i was thinking that the airbus mini function could cause an issue. from the replies, i gather that this could cause problems but atc been on top of the situation would see us catching up or causing a flow problem. just trying to see the side of the controller as i hate mucking there job up, its tough enough whithout us maybe not understanding the problems this may cause. i know 3tcas and alike can help us see our closer rate and either slow ourselves or mention it, but would using this info just increase your problems on top of the ground speed mini function, i.e. we slow using selected speed then manage the speed back to ground speed mini, i guess then this buggers up the aircraft behind if we do this.
cheers
HEATHROW DIRECTOR
10th May 2011, 06:53
Having read that last post I don't believe this person is a real pilot. Heck... he's illiterate!!