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Airbus A320 crashed in Southern France

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Airbus A320 crashed in Southern France

Old 25th Mar 2015, 11:29
  #521 (permalink)  
 
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Originally Posted by vapilot2004 View Post
Agreed but there is no normal operational reason for an oscillation in the resulting V path.
Yes there is. Not sure which but you're not sure of.

In an IAS/Mach Idle descent the VS and thus vertical path will vary with wind, temperature/density changes, vertical currents, IAS/Mach switchover and other factors. An Open Descent is always quite variable in terms of achieved profile.
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Old 25th Mar 2015, 11:33
  #522 (permalink)  
 
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@ HubertWilkins

The article is good. It sheds a light on the pros and cons of the oxygen rule under FAA. Even if wearing an O2 mask before de-pressurisation MIGHT have saved this flight, (We don't know anything yet) there are very good arguments to be made for the European rules concerning oxygen.

The fact that the majority of pilots, generally a very responsible group of people, seem to ignore this rule might be an indication that the rule might perhaps be wrong...
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Old 25th Mar 2015, 11:33
  #523 (permalink)  
 
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French ATC

There were undoubtedly many calls to the acft. French ATC are known for being alert, especially near borders... they'll send you a couple friendly Mirage 2000s if you miss an entry time or forget to report when entering their ADIZ.

They were aware something was very wrong, but most likely powerless (and frustrated) witnesses, like Greek ATC in the Helios case.
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Old 25th Mar 2015, 11:36
  #524 (permalink)  
 
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Double windscreen failure seems remote unless it was caused by an impact.
It would also preclude any donning of masks much less A/P manipulation to start the descent. A slow failure that caused the crew to first start a descent out of precaution followed by something more catastrophic more likely.
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Old 25th Mar 2015, 11:37
  #525 (permalink)  
 
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vapilot2004 says
You don't set a rate of descent. You basically close thrust ( open descent on the Bus ) and then the Elevators control the speed that you have selected. Therefore the rate of descent will vary.
Agreed but there is no normal operational reason for an oscillation in the resulting V path.
no normal operational reason for an oscillation in the resulting V path
In nil wind that would true, but the real world is not like that. As you descend (or climb) the head/tail wind component will change. That will change your IAS and if you have select a 'pitch for speed' mode, the pitch attitude (and thus the V/S) will change to maintain the selected speed.
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Old 25th Mar 2015, 11:39
  #526 (permalink)  
 
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Below are the IAS approximations taken from groundspeed readouts from FR24 for the flight. They were taken as a TAS and converted to an CAS, therefore they are not corrected for wind effect. There was a southerly blowing at around 13 knots in the lower levels, rising to about 30 knots in the higher levels.

I don't know how closely these correspond to the actual IAS considering all the possible errors and the fact that the aircraft was descending rapidly, however...

VMO/MMO for the A320 are 350 knots/0.82

32625 CAS 296 EAS 279 MN .823

28875 CAS 313 EAS 297 MN .805

24650 CAS 343 EAS 328 MN .81

20300 CAS 358 EAS 345

17000 CAS 355 EAS 345

15000 CAS 355 EAS 346

13300 CAS 358 EAS 351

11125 CAS 355 EAS 349

9975 CAS 350 EAS 345

8259 CAS 342 EAS 339

6925 CAS 343 EAS 340

There remains the strong possiblity that the hi speed protections activated during the descent. They activate @VMO +6

Normal Law - High Speed Protection

When high speed protection is active:

The autopilot disconnects

High speed aural warning is heard

Automatic pitch trimming stops

Bank angle limit is reduced from 67° to 45°

Positive spiral static stability is introduced to 0° bank angle (instead of 33° bank angle in normal law), so that when the side stick is release it always returns to 0° bank angle instead of 33° bank angle

High speed protection can be overridden, but side stick nose-down authority is reduced and a positive pitch-up command is introduced

If the stick is released, the airplane continues to pitch-up until the airspeed slows to VMO/MMO at which point the high speed protection is deactivated and normal control laws are restored.


The questions are whether this aircraft went fast enough to activate the high speed protections? If it did, why didn't it pitch up, and what was it doing flying so fast in the first place?

If pilot incapacitation occurred, why did the Auto-pilot maintain maximum possible speed, and why did it not capture an altitude selected on the FCU?

The standard drill for an emergency descent involves keeping the autopilot engaged if possible, dialing a lower FCU altitude, turning off the airway and commencing the descent by selecting Open Des.

The aircraft continued on track but commenced descending at maximum speed, so none of that appears to have been done. Unless there was a massive un-correctable error in the Auto-flight system, there had to be pilot intervention to get it to do that.

This is a very strange accident.
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Old 25th Mar 2015, 11:40
  #527 (permalink)  
 
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If it is a fwd fuselage structural failure (e.g. windscreen) the investigators, I think, will have their work cutout A high speed impact into a steep rockface will likely leave much evidence destroyed, and the chance of finding anything under the original failure point small, but possible. The crash site will be very hard to confirm "things not found" were never there and thus missing prior the crash.

The 14K V/S indication in the short cruise I'd be interested in a technical explanation of how/where it has come from? Mode S? Where does ADS-B get (or derive) this from?
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Old 25th Mar 2015, 11:42
  #528 (permalink)  
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There were undoubtedly many calls to the acft.
yes, a lot .
Last normal communication from the crew was one min before start descent.
then nothing.
It is quite traumatic for a controller I can tell you when you watch an aircraft you control go down.
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Old 25th Mar 2015, 11:46
  #529 (permalink)  
 
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The standard drill for an emergency descent involves keeping the autopilot engaged if possible, dialling a lower FCU altitude, turning off the airway and commencing the descent by selecting Open Des
If your not incapacitated or your brain isn't so scrambled that your inputs are as to the book ?
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Old 25th Mar 2015, 11:46
  #530 (permalink)  
 
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Yes Nigel, the disposition and fragmentation of wreckage will undoubtedly make the task of indentifying the windshield and whether it was separated prior to impact. However in the event that it did blow out at 38,000feet, then as the aircraft commenced a descent just about when it was coasting in, then the evidence will be lying either in the water, close to shore or further inland, not with the main wreckage.
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Old 25th Mar 2015, 11:48
  #531 (permalink)  
 
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Full Quote from Avherald

FORUM SECTION

Anonymous posting here:

http://avherald.com/h?article=483a5651&opt=0

Structural failure
By Uknown on Wednesday, Mar 25th 2015 09:01Z

CVR data has been read. It seems structural failure (windshield? not determined yet)..It was quick... sound of cracks,but crew initiated emergency descent by autopilot and then they weren't heard anymore. Autopilot was on during whole descent, but disconnected automatically shortly before impact when GPWS alerts appeared.
Again!
FORUM SECTION, referring to an "anonymous" post, on another FORUM


All this conjecture.


People, STOP the conjecture. Until the investigation is done, NO-ONE will know what happened.
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Old 25th Mar 2015, 11:48
  #532 (permalink)  
 
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BEA has some pictures of the CVR here:

Mediathèque

Memory unit seems to be in good shape
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Old 25th Mar 2015, 11:49
  #533 (permalink)  
 
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Does anybody know if the correct level off altitude was 6800ft (as reported on some sites) or FL068 (as reported on avherald)?
The "data" I saw from FR24 stopped at 6800', did not "level at". Systems showing it levelling off may well be "predictive" when the data stream is lost?

AvHerald had someone deduce an accurate crash location which my Google Earth makes ~5500'. The ridge beyond it GE says is ~6100'. Very roughly, if you take the last FR24 position, the RoD then, and run forward to the crash site, another 1000'-1500' lost is "in the ballpark" (I've not spent a lot of time on this, so do not treat with much confidence).

As I said above, if it was an OP DES descent, the selected Altitude (which the AP would level off at) should have been transmitted over Mode S the whole way down, so the BEA may reveal that later today?
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Old 25th Mar 2015, 11:49
  #534 (permalink)  
 
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Maybe FL 100

FL 100 set maybe but a/c unable to level off with A/P disengaged!
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Old 25th Mar 2015, 11:54
  #535 (permalink)  
 
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@Cagedh
Just to be clear, we are talking about the US rule which states:
if one pilot leaves the cockpit at XXX level, then the remaining pilot must don O2 mask and keep it on until the other pilot returns.

I guess we can agree to disagree, I believe this rule is sensible.

If there are two pilots in the office and decompression occurs, there are two heads trying to solve one issue. decent odds.
If only one guy is there the odds are halved, so it is good sense to have a head start.
That is what I believe.
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Old 25th Mar 2015, 11:56
  #536 (permalink)  
 
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The 14K V/S indication in the short cruise I'd be interested in a technical explanation of how/where it has come from? Mode S? Where does ADS-B get (or derive) this from?
The ADS-B transmissions include altitude and speed, direction amongst other information but do not give v/s. I believe the -14k V/S is a blip from FR24 processing as I'm sure it showed the same altitude of 38k before and after this event.
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Old 25th Mar 2015, 11:56
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Old 25th Mar 2015, 11:58
  #538 (permalink)  
 
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If it were a windshield failure @ FL380, it would be extremely violent. Question would be how long till they recover from the shock, and whether ie Oxy masks can be found quickly or dislodged ?
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Old 25th Mar 2015, 11:59
  #539 (permalink)  
 
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People, STOP the conjecture. Until the investigation is done, NO-ONE will know what happened.
This is predominantly a professional pilots forum? It may have changed so that every Tom Dick and Harry can input into it but whether its a single engine Piston where a family of four have been killed or an Airline where many souls are lost talking about possible causes is beneficial.

Why? because with all these tragic accidents information and lessons learnt are best taken in when the horror and impact of the accident is fresh in pilots minds.

Sadly a year down the line when the AAIB reports are released the event is long forgotten.

Sadly even AAIB reports are not conclusive

Sadly some accidents remain a mystery (Malaysian airline) and the reasons will Never be found.

As long as posters do not post as FACT and do so responsibly discussing the possibilities can only be educational and positive.
No one can turn the clock back but we can look forward

Last edited by Pace; 25th Mar 2015 at 12:13.
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Old 25th Mar 2015, 12:00
  #540 (permalink)  
 
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Does anybody know if the correct level off altitude was 6800ft (as reported on some sites) or FL068 (as reported on avherald)?
ADS-B data is always QNE (=1013mb)

Anybody who wants to analyze ADS-B data go to the FR24 twitter page, then load the csv data file with 7,900+ data points to Excel. Packet interval is 1 sec and less. Apply an auto filter to receiver 1418. This receiver has continous uncorrupted and consistent data until the final packet. http://www.pprune.org/rumours-news/5...ml#post8914431

If you filter other receivers you can see that some deliver nonsens and must be ignored. The -14,000 fpm tale V/S is not present on FR24, it must be a different source. Note that Flightaware and Planefinder do not have as near as many receivers in the area as FR24.
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