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BAW492 diversion at Gibraltar

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BAW492 diversion at Gibraltar

Old 2nd Mar 2019, 10:47
  #121 (permalink)  
 
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What report can we expect?

Originally Posted by pineteam View Post
Very plausible with a set of crew who never hand fly... In the other hand I never saw or heard an A 320 behaving like this with AP. But I might be wrong. Let's wait for the final report. Hopefully we can access it.
What kind of report can we expect?
If there was a fault wouldn’t this be classed as a incident? The official explation is that it was caused by weather conditions.
I believe the aircraft flew back after we were dropped off at Malaga, would this confirm no issues with the aircraft?

It’s a pity that data on all abortive landings is not shared automatically.

Thanks everyone for sharing experience and theories. I will be back on this route next week, not the scariest landing I’ve had at Gibraltar in terms of weather but just sensed a loss of control on this landing.
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Old 2nd Mar 2019, 11:13
  #122 (permalink)  
 
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I guess this will be remembered as the "Gibraltar Rock & Roll Approach"...
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Old 2nd Mar 2019, 12:16
  #123 (permalink)  
 
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Originally Posted by Kerosene Kraut View Post
If PIO why would it last for so long and be so regular? If not why leave on the autopilot at all?
I think folk can stop going on about PIO now. Two of the posts above have clarified that the autopilot was on throughout.

The other “heard from a mate in BA...” story is clearly nonsense.
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Old 2nd Mar 2019, 15:38
  #124 (permalink)  
 
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Originally Posted by PassengerOnBoard
If there was a fault wouldn’t this be classed as a incident?
If the Air Accident Investigation Branch (and I think it comes under their jurisdiction, in part at least because it is a UK registered aircraft) considers it to be a 'serious incident' then they can elect to investigate it. Whist there is a definition of a 'serious incident', and some examples of events that would be classed as such, in a European regulation on the topic, it is still a rather subjective term.

Although I can't recall the details, I recall an event outside the UK a few years back that I don't think was formally reported initially but was well covered in the media and which was called in by the accident investigation agency - it sticks in my mind for the very reason that it was called in for investigation even though no report was filed.
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Old 2nd Mar 2019, 19:21
  #125 (permalink)  
 
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Gibralter have recently introduced RNP(AR) approaches (last year?). Boeing and Naverus got down to 0.11nm minima on the 737. Maybe Airbus tried to outdo them and went for a 0.1nm minima. To achieve this it seems they used some software intended for tracking an engine failure/engine out. Bank angle limits on say an ILS are single figures, but on an RNP(AR) approach it is 30 degrees - but that should be a constant bank to achieve an RF leg. Somehow it got lost in translation and Airbus software thinks you can now roll thru a 60 degree arc. A320 roll rates are 30 degrees/second clean, 25 deg/sec dirty and only 15 deg/sec in manual flight.
The RNP(AR) software “operates outside normal flight control laws” and it seems roll rates are unlimited. The software gets stuck in a “loop” rolling thru a 60 degree arc. It will do the same in the SIM if you put in a spot wind of 40|45 knots (crosswind) and mod/sev turbulence - on an RNP(AR) approach. It is too sensitive and too reactive.
It’s a bit like the Airbus Rudder Limiter. It seems to have got lost in translation and software also limits rudder pedal movement. As little as 1 inch of rudder pedal travel will achieve full rudder deflection for the given speed, as Air Canada A319 ACA 190 encountered 10 Jan 2008. Explained in in the report under “Rudder Control System”. (TSB GC CA a08w0007 2008)
Should a bank angle limit become a roll limit (60 degree arc), should a Rudder Limiter limit rudder pedal travel or just rudder deflection?
The crew in Gibralter most likely experienced some Spatial Disorientation and what was perceived/reported as “turbulence” was in fact as a result of g loading and spoiler deflection/buffet. Recommendation for spatial disorientation is to keep the autopilot engaged - crew did everything by the book. Info plus some accident history on site code7700.com under spatial disorientation.





Last edited by BlueUpBrownDown; 3rd Mar 2019 at 03:09.
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Old 2nd Mar 2019, 20:16
  #126 (permalink)  
 
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Auto Pilot/FG Architecture.
The FG has two loops – essentially two software logic circuits. - the Inner Loop - the Guidance loop The inner loop is the more reactive one and gives short-term commands while the guidance loop has more of a mid-term action/role. The two loops are controlled by two different cards/processors. When in approach, the gain of the inner loop is different from cruise so it is more reactive to any perturbation that could make the A/C deviate from its path. With FMS release 1A when using the RNP AR mode the gain laws have been tightened so the rate of change to guidance commands is enhanced and will mean more rapid adjustment if necessary to maintain desired flight path accuracy.

Airbus Findings
The aircraft was subjected to a lateral gust of wind which was the root cause of the commencement of oscillations. The Auto Pilot inner loop, being more reactive in RNP approach mode, was the cause of the abrupt roll. It was confirmed in simulator tests that these dedicated laws can, in a few cases, generate lateral oscillations when associated with some specific strong lateral gusts. These oscillations did not exceed the RNP AR limits and oscillations remained contained.

Summary
Abrupt roll oscillations may be experienced on an RNP AR approach in gusty conditions. This is most likely associated with the A/P FG architecture. The aircraft should stay within its RNP XX boundaries and the A/P should remain engaged.
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Old 2nd Mar 2019, 21:17
  #127 (permalink)  
 
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If the autopilot was engaged throughout the autopilot induced oscillations, what happened to clicking out and manually taking control?
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Old 2nd Mar 2019, 22:14
  #128 (permalink)  
 
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Originally Posted by BlueUpBrownDown View Post
Auto Pilot/FG Architecture.
The FG has two loops – essentially two software logic circuits. - the Inner Loop - the Guidance loop The inner loop is the more reactive one and gives short-term commands while the guidance loop has more of a mid-term action/role. The two loops are controlled by two different cards/processors. When in approach, the gain of the inner loop is different from cruise so it is more reactive to any perturbation that could make the A/C deviate from its path. With FMS release 1A when using the RNP AR mode the gain laws have been tightened so the rate of change to guidance commands is enhanced and will mean more rapid adjustment if necessary to maintain desired flight path accuracy.

Airbus Findings
The aircraft was subjected to a lateral gust of wind which was the root cause of the commencement of oscillations. The Auto Pilot inner loop, being more reactive in RNP approach mode, was the cause of the abrupt roll. It was confirmed in simulator tests that these dedicated laws can, in a few cases, generate lateral oscillations when associated with some specific strong lateral gusts. These oscillations did not exceed the RNP AR limits and oscillations remained contained.

Summary
Abrupt roll oscillations may be experienced on an RNP AR approach in gusty conditions. This is most likely associated with the A/P FG architecture. The aircraft should stay within its RNP XX boundaries and the A/P should remain engaged.

In case it’s not clear, the above quote is related to a different roll oscillation incident than Gibraltar. Note also that the recommendation is to leave the A/P engaged.
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Old 3rd Mar 2019, 04:50
  #129 (permalink)  
 
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Originally Posted by Doug E Style
If you can say what your actions would have been after having a bit of a think about it having watched a couple of posted videos, rather than the information available to the crew, not to mention the considerable “startle-factor”, then that’s a bit worrying.
What would be worrying would be sitting in the back of your aircraft while that was going on for almost 60 seconds with you not doing anything about it. And if your startle factor lasted that long, in broad daylight, that is also a worry.
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Old 3rd Mar 2019, 08:09
  #130 (permalink)  
 
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Originally Posted by Capn Bloggs View Post
What would be worrying would be sitting in the back of your aircraft while that was going on for almost 60 seconds with you not doing anything about it. And if your startle factor lasted that long, in broad daylight, that is also a worry.
It's concerning isn't it!
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Old 3rd Mar 2019, 09:28
  #131 (permalink)  
 
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Why would an aircraft manufacturer recommend keeping the autopilot connected in a situation where the auto flight system clearly is not working as it should?
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Old 3rd Mar 2019, 13:11
  #132 (permalink)  
 
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Originally Posted by BlueUpBrownDown View Post
Gibralter have recently introduced RNP(AR) approaches (last year?). Boeing and Naverus got down to 0.11nm minima on the 737. Maybe Airbus tried to outdo them and went for a 0.1nm minima.
The lowest RNP line of minima at LXGB on the public RNP AR approaches is RNP 0.12.
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Old 3rd Mar 2019, 15:01
  #133 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post
Why would an aircraft manufacturer recommend keeping the autopilot connected in a situation where the auto flight system clearly is not working as it should?
My 2 cents: Because its bad for sales saying your automatic systems can't handle the tasks they've been designed for.

Now ask yourself: what would the average TRE in your airline say you should do on an RNP approach in IMC with a sudden a/p failure? My bet would be most will say to g/a and ask for another type of approach.

This is the mentality I've found most common during my time with 2 of Europe's largest carriers. So I can clearly see why MANY flight crews would sit and watch the a/p misbehave on an RNP approach and do nothing, even in vmc.

The same many are usually great at quoting details from the fcoms though.
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Old 4th Mar 2019, 02:30
  #134 (permalink)  
 
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Airbus Golden rule#4 surely over rules that recommendation: « Take actions If things do not go as expexted. »
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Old 4th Mar 2019, 05:17
  #135 (permalink)  
 
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It’s fairly likely the idea of disconnecting the AP was thought of and discussed during the incident; after all, the oscillations went on for some time.

You’re sat in the pilot’s seat of a fully FBW aeroplane, which develops an uncomfortable but contained roll oscillation with AP engaged. You’re climbing away from the ground and the wobbles appear to be getting neither better nor worse, giving time for some diagnosis/options/action. One possible scenario could be that there is a severe flight control issue which the AP and/or envelope protection is only just dealing with and going “manual” might make the situation worse or lead to LOC. There is always the pressure to DO SOMETHING but what if the cure is worse than the disease? The AP might readily disengage but not want to go back in...

I’m pretty sure that if the rolling had carried on after config. changes, at some point they’d have agreed to take the AP out. After all, landing in that condition is not going to be fun.
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Old 4th Mar 2019, 06:56
  #136 (permalink)  
 
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Originally Posted by ManaAdaSystem View Post
Why would an aircraft manufacturer recommend keeping the autopilot connected in a situation where the auto flight system clearly is not working as it should?
Are you referring to BlueUpBrownDown's post?
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Old 11th Mar 2019, 11:52
  #137 (permalink)  
 
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Non disengagement of the autopilot

Originated in BEA where some of the bomber boys could not cope with the Trident especially on approach way behind the drag curve and was the reason their monitored approach was developed. It was also the reason that Hamble was taken over by the corporations in 1960 when there were thousands of ex military pilots available.
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Old 12th Mar 2019, 16:07
  #138 (permalink)  
 
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Key facts from our Airbus Flight Tech Manager:

Autopilot remained on throughout. Conf Full with Gear down in FINAL APP mode. Windshear at 700ft followed by GPWS "sink rate". TOGA with configuration unchanged as per windshear SOPs. After selecting Conf 3 roll reduced, accelerated and cleaned up normally.
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Old 12th Mar 2019, 17:57
  #139 (permalink)  
 
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Does your flight manager believe that it was acceptable

Or have procedures or programming been changed?
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Old 13th Mar 2019, 16:18
  #140 (permalink)  
 
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Blind Pew, you obviously have an axe to grind. Whatever your motives are it’s not very edifying and suggests bitterness and a lack of factual knowledge.

For your your education the monitored approach was developed to combat the three or so seconds it takes the human brain to switch cognitive tasks, in this case the transition from instrument flying to visual flying at CAT 1 (or in past times CAT 2) minima. The science showed (shows) that a pilot already processing visual references as soon as they became available made (makes) a better job of the final approach, flare and landing. Some types / companies still legitimately perform manual landings off a CAT 2 approach, BA doesn’t.

FWIW as a recent product of the above training department it is top notch from the top down.

I’d suggest this event was a surprise for everybody involved, was well handled (others may have chosen to do it differently and that may well have resulted in just as good an outcome), and you can bet the manufacturer is working on it as a matter of urgency.

LD
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