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Airbus questions that I cannot resolve!!!!!

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Airbus questions that I cannot resolve!!!!!

Old 15th Nov 2019, 03:44
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Airbus questions that I cannot resolve!!!!!

Greetings all,

I dont usually turn to forums to solve technical questions about the Airbus however our FCOM’s have been slowly “boeingised” at my airline and as such some information that has been readily available for years is no longer contained in our version and I no longer have older original Airbus copies of FCOM from previous airlines to consult.

Firstly, many of us have noticed that on the A319 following the use of speedbrake during descent, once configured for landing and stable, the autothrust carries 10-15 knots extra speed on top of VAPP. The only way to get back to VAPP is to disengage and reengage the auto-thrust. I am sure in a previous life seeing documentation to this effect however my present company has nothing written about it and I am struggling to find anyone in the training department that even understands what I am talking about. I very rarely fly the A319 as its only a small part of our fleet. Can anyone shed some light on this?

Secondly, my recent sim dealt with windshear as a result of the new upset training syllabus and during our briefing, the instructor mentioned that when receiving a predictive windshear warning it was company policy to turn away from the windshear displayed on the ND. However, I am certain that in several previous companies (many years ago admittedly) the procedure specifically advised not to turn away from a windshear icon on the ND. Can anybody provide some history to this issue, was there or is there still an FCOM recommendation NOT to turn away from a windshear icon on the ND?

Cheers all and thanks for any input
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Old 15th Nov 2019, 06:13
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Hi Oicur

I don't know if it is of any help by FCTM says ... if a predictive W/S caution is triggered during initial climb, the flight crew must ... ensure that the flight path does not include areas with suspected W/S.

Bye

Francesco
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Old 15th Nov 2019, 06:56
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For the windshear, could you be confusing predictive windshear with the windshear escape? In a windshear escape you maintain wings level, so no turns away from what may be more windshear ahead of you. On the other hand, predictive windshear is just warning of windshear ahead and you are free to manoeuvre because you aren't in any actual windshear yet.
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Old 15th Nov 2019, 07:07
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Predictive wind sheer tells if you continue on the present track 3 miles straight ahead you could kill yourself. Now it's your choice.
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Old 15th Nov 2019, 07:28
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Originally Posted by oicur12.again View Post
Greetings all,

I dont usually turn to forums to solve technical questions about the Airbus however our FCOM’s have been slowly “boeingised” at my airline and as such some information that has been readily available for years is no longer contained in our version and I no longer have older original Airbus copies of FCOM from previous airlines to consult.

Firstly, many of us have noticed that on the A319 following the use of speedbrake during descent, once configured for landing and stable, the autothrust carries 10-15 knots extra speed on top of VAPP. The only way to get back to VAPP is to disengage and reengage the auto-thrust. I am sure in a previous life seeing documentation to this effect however my present company has nothing written about it and I am struggling to find anyone in the training department that even understands what I am talking about. I very rarely fly the A319 as its only a small part of our fleet. Can anyone shed some light on this?

Secondly, my recent sim dealt with windshear as a result of the new upset training syllabus and during our briefing, the instructor mentioned that when receiving a predictive windshear warning it was company policy to turn away from the windshear displayed on the ND. However, I am certain that in several previous companies (many years ago admittedly) the procedure specifically advised not to turn away from a windshear icon on the ND. Can anybody provide some history to this issue, was there or is there still an FCOM recommendation NOT to turn away from a windshear icon on the ND?

Cheers all and thanks for any input
The first thing you are seeing is most likely ground speed mini. This is not annunciated to the crew, but it is active whenever the auto thrust is engaged. It takes the tower reported winds entered into PERF APPR page and calculates a minimum energy level the aircraft should have at touchdown - aka "ground speed mini". During the approach, the FMGS computes the speed target, based on the actual winds experienced by the aircraft, to maintain the ground speed above the minimum target. This is your real time gust factor protection and why you do not insert a gust protection yourself as you might in other aircraft. By disconnecting the auto thrust, you are eliminating your gust protection. Again, this function is not annunciated to the crew, but you can tell it is active whenever the speed target goes above the targeted VAPP during the approach.
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Old 15th Nov 2019, 07:57
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The historic use of your speed brake during the descent will have nothing to do with a new Vapp. And as other posters have mentioned what you are seeing is likely ground speed mini, designed to maintain a constant energy level, if you have a magenta speed target which reads above the Vapp visible in the FMGC, then this is almost certainly it.

Many years ago, and if I recall correctly airbus did have a feature (or maybe it was just my company as they had some quirky sop's) where you could activate 'phase advance'. Which meant clicking the thrust levers forward out of the climb detente for a split second in order to cause the aircraft thrust to increase... but that was removed and is no longer procedure.

I'd probably have a read about ground speed mini, because as other posters have said, by disabling it you are removing a safety feature.
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Old 15th Nov 2019, 09:24
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The use of speed brake while the flaps are moving can cause a discrepancy where the aircraft flies Vapp+10 kts. You’d indeed recycle the auto thrust to get rid of it. Considering that it’s a “bug” it happens surprisingly often. It’s in the 319 only. The only reference I have is to our own OMB however.


For the ground speed mini fans; there’s been a subtle but significant change in the logic comparing the NEO to the CEO. The NEO only adds a third of the difference in wind, compared to the whole difference on the CEO.

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Old 15th Nov 2019, 10:27
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I’ve never seen the 319 do that. If disconnecting the AT fixes it, it’s almost certainly not GSmini.
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Old 15th Nov 2019, 10:42
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The description you gave is strange, if disconnecting the AT fixes the problem then it is probably not the GSmini. GSmini would be the obvious answer, when on approach did you disconnect an reconnect AT? The AT system can be quite lazy so if the OFF/ON of the AT was done in the latter portion of an approach it might be that it simply hasn't redone calculations and made the input yet to achieve the targeted GSmini speed speed. Next approach maybe try the same OFF/ON selection but at an earlier time on the approach and see if it is still carrying the extra speed or not. If it does reset itself still like you have mentioned above I would ask your airlines tech pilot for some clarification.
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Old 15th Nov 2019, 10:46
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oicur12.again
1) yes, known behaviour. Same as you I've seen it admitted and described by AB somewhere, but no clue where that was.

2) answered already.
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Old 15th Nov 2019, 11:48
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1. Never seen it across 319s of moderate age and different engine types.

Your tech pilots should be able to answer if it's peculiar to your fleet/FMGC logic or some other thing, or at least email Airbus for tech request for one.
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Old 15th Nov 2019, 13:20
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The problem that the original poster described is nothing to do with groundspeed mini and is refferred to in documentation as 'autothrust misbehaviour'. It only ever effected the A319 and was cured (allegedly) when the FMCG S7 update was introduced.

As a result its very difficult to find reference to it in any current documentation. All I can find at the moment from some old stuff I have on a disk is a comparison chart as to which of our fleet suffered from various OEB items and Autothrust Misbehaviour is listed as ATA 22 against all our 319s.
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Old 15th Nov 2019, 17:59
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Originally Posted by compressor stall View Post
1. Never seen it across 319s of moderate age and different engine types.

Your tech pilots should be able to answer if it's peculiar to your fleet/FMGC logic or some other thing, or at least email Airbus for tech request for one.
Well, I can say that it used to be an everyday occurrence on older 319s at our US airline; if you used speedbrakes with flaps 2 or greater, the speed would never come back to Vapp. It would settle about 3-5 knots faster. You could disconnect and reconnect Autothrust, and then the speed would be correct.

Speedbrakes with Flaps 1 would not show this discrepancy.

Some recent (within the past two years or so) change got rid of this glitch.
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Old 15th Nov 2019, 18:54
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Is it possible that it is a software(as mentioned by other posters) that has had an update but not all aircraft have been updated. Are the software updates mandatory installation of an option to purchase with some airlines deciding not to update in order to save money.
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Old 17th Nov 2019, 00:21
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As pointed out by several posters here with thanks, the A319 autothrust issue is indeed a case of “autothrust misbehavior” and has now been rectified on our fleet. It is not related to GS mini.

The PWS issue is not so simple.

“Predictive wind sheer tells if you continue on the present track 3 miles straight ahead you could kill yourself. Now it's your choice.”

True, but PWS is only looking at 40 degrees left and right of aircraft heading, less than half the sky. A turn away from a windshear icon on the nose could turn you into a worse windshear event presently unseen by the system.

I have managed to find a reference on the Honeywell web page that advises:

“Doppler processing limits the windshear detection region to approximately +/-40 degrees ahead of the aircraft. It is not uncommon to have multiple microbursts in the same area, so a turn to avoid one microburst might place the aircraft in a banked turn and in position to encounter another possibly more severe microburst.”

Last edited by oicur12.again; 17th Nov 2019 at 02:59.
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Old 17th Nov 2019, 08:12
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Originally Posted by oicur12.again View Post
As pointed out by several posters here with thanks, the A319 autothrust issue is indeed a case of “autothrust misbehavior” and has now been rectified on our fleet. It is not related to GS mini.

The PWS issue is not so simple.

“Predictive wind sheer tells if you continue on the present track 3 miles straight ahead you could kill yourself. Now it's your choice.”

True, but PWS is only looking at 40 degrees left and right of aircraft heading, less than half the sky. A turn away from a windshear icon on the nose could turn you into a worse windshear event presently unseen by the system.

I have managed to find a reference on the Honeywell web page that advises:

“Doppler processing limits the windshear detection region to approximately +/-40 degrees ahead of the aircraft. It is not uncommon to have multiple microbursts in the same area, so a turn to avoid one microburst might place the aircraft in a banked turn and in position to encounter another possibly more severe microburst.”
Apart from PWS you already have full radar picture in front you. PWS only displays the worst area ahead. The weather assessment should have been done before take off roll. And if you had entire ND full of echoes then either take off should have been postponed or done in different direction RW. But after PWS warning there is no question of continuing in same direction. Don't forget even takeoff needs to be abandoned with PWS warning. ​​​Radar manufacturer has only legally covered himself by stating that things could be worse outside that. What is outside PWS range is unknown but what is front is definitely dangerous. That single statement is not a license to go through what's in front. When you start the turn PWS will cover that area also. You may have to do 360°. If there was no PWS would you go through a CB in front?
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Old 17th Nov 2019, 08:23
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Originally Posted by oicur12.again View Post
As pointed out by several posters here with thanks, the A319 autothrust issue is indeed a case of “autothrust misbehavior” and has now been rectified on our fleet. It is not related to GS mini.

The PWS issue is not so simple.

“Predictive wind sheer tells if you continue on the present track 3 miles straight ahead you could kill yourself. Now it's your choice.”

True, but PWS is only looking at 40 degrees left and right of aircraft heading, less than half the sky. A turn away from a windshear icon on the nose could turn you into a worse windshear event presently unseen by the system.

I have managed to find a reference on the Honeywell web page that advises:

“Doppler processing limits the windshear detection region to approximately +/-40 degrees ahead of the aircraft. It is not uncommon to have multiple microbursts in the same area, so a turn to avoid one microburst might place the aircraft in a banked turn and in position to encounter another possibly more severe microburst.”
erm, does that Honeywell statement refer to Predictive windshear detection, or Actual Windshear encounter.

Ttfn
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Old 17th Nov 2019, 17:14
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Predictive
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Old 20th Nov 2019, 14:16
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PWS was developed in the aftermath of DELTA191 crash at DWF when it went through the only CB on approach. It only operates below 2300ft. It even automatically activates with weather radar off. Surely if they didn't want you to take avoidance they wouldn't have bothered to do all that. At takeoff point if your radar scope is full you shouldn't takeoff in that direction.
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Old 21st Nov 2019, 22:41
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I would say predictive from my experience.
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