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AF447 Thread No. 3

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AF447 Thread No. 3

Old 31st May 2011, 05:55
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Graybeard

Yesterday when posting the FDR traces for the Jetstar A330 incident, I mulled over the static port problem, then looked at the ECAM messages and realized that the sequence of events was very similar to AF447. So, getting back to the TCAS fail message, I'm starting to feel that the ALT supplied to the Transponder changed at a rapid rate, i.e. the speed correction value changed, and the TCAS determined the rate of change wasn't valid and shut-up shop.

Do you think that could fit the bill?

Last edited by mm43; 31st May 2011 at 06:56. Reason: added the speed correction value
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Old 31st May 2011, 06:29
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Cool

Hi,

Just a general thought - does the Flight Path Vector display use air data at all or is it just inertial? Would this have helped the pilots' SA in this situation?
HUD ?
A good question for gums or other jet fighters pilots here ......
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Old 31st May 2011, 07:16
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fizz57
... does the Flight Path Vector display use air data at all or is it just inertial?
Boeing use the inertial method, and Airbus use barometric vertical speed and inertial groundspeed and attitude.

Last edited by mm43; 31st May 2011 at 08:05. Reason: gave the right answer as per HN39
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Old 31st May 2011, 07:45
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... does the Flight Path Vector display use air data at all or is it just inertial?
Embraer (Honeywell EPIC) uses both and the procedure is to ignore the FPA with unreliable airspeed.

Hi,

Seem's a little bit ironical ... but modern military jet fighters planes have an HUD with many interesting datas just in face of pilot eyes .. all this for assure the safety of one soul .. and some tons of metal and weapons .. and airliners have not this for assure the safety of hundred of souls and some tons of metal.
HUD just repeating what's available downstairs in the cruise so doesn't offer any enhancements when IMC.
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Old 31st May 2011, 08:02
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On the fundamental issue of the design of cockpit information systems

@ventus45

"Worth a read"
Good references - certainly worth the read..

Many thanks...
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Old 31st May 2011, 08:02
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mm43 #844;

Airbus FPV uses barometric vertical speed and inertial groundspeed and attitude (explained in BEA report).

mattewsjl #825;

I agree entirely with your analysis. The airplane stalled after 2:10:51.

JD-EE #830;

First three sentences agreed. However at FL375, 215 kCAS, AoA=4 the airplane is not stalled: the normal acceleration is less than 1 (approx. 0.8) hence v/s is decreasing.
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Old 31st May 2011, 08:09
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HN39
Airbus use barometric vertical speed and inertial groundspeed and attitude (explained in BEA report).
Should have read the report again! Many thanks and I have corrected the error.
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Old 31st May 2011, 08:15
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Apologies if this has already been spoken about or dismissed - I haven't been able to read all 43 pages so far.

Some of the aspects of this accident just made me recall the following passage from and incident report (although RVSM/TCAS related) involving an A340 entering turbulence over the North Atlantic.

Feel free to disregard if irrelevant.

A340 commander's report
At FL 360 the A340 was 1000 feet below the maximum cruising level displayed on the Flight
Management and Guidance System (FMGS). The commander was expecting a turbulence
encounter around 59N 20W and when the aircraft first entered light turbulence he made a cabin
announcement and switched on the seat belt signs. Shortly before the AIRPROX event he
experienced moderate turbulence and noticed outside air temperature changes. Suddenly the aircraft
began to climb, the Master Warning sounded and the autopilot self-disengaged as the aircraft
exceeded the speed limit of 0.86 Mach. The indicated airspeed dropped below VLS (the lowest
selectable) as the aircraft climbed and the commander took manual control of the aircraft because
neither autopilot would engage. The crew subsequently reported the incident to Shanwick on HF
radio and using their TCAS, they descended back to FL 360 in a safe area. At the time of the
AIRPROX the commander estimated the aircraft were one mile apart laterally. After landing at
New York the commander had the aircraft inspected by technical staff but no defects were found.
There were no injuries on board the aircraft.
The commander could not remember the sequence of warnings but he did recall being unable to reengage
either autopilot which prompted him to make manual control inputs. He also remembered
seeing an 'Alpha Lock' warning displayed on his Primary Flying Display.
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Old 31st May 2011, 08:25
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Picture still valid?

Re http://www.pprune.org/tech-log/45283...ml#post6483173

If I remember correctly, this chart is part of the analysis of Tim Vasquez of 2009. Is there an updated version around corrected for the now known exactflightpath? As stormcells are very narrow, it might make a substantial difference to the picture...
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Old 31st May 2011, 08:36
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@bekolblockage

You have to go back more than 43 pages! The ballistic zoom-climb trajectory demonstrated by the A340 was suggested as soon as the proximity of the crash site to LKP confirmed - and the FDR plots in Appendix B of the AAIB report re-published a couple of weeks ago. But the A340 in daylight did not lose air-speeds so flight control laws and protections not the same as AF447 - but was way above safe height and must have been very close to stall at the apogee at FL 384 "where the airspeed had decayed to 205 KIAS and 0.67 Mach even though full thrust had been applied". Full thrust was from protection even though A/T off.

[edit] Note that the pitch-up and climb was auto control system induced, the recovery thanks to the pilot requiring bold inputs to break an AoA hold law. There is no mention in the report of stall warning so pitch and AoA correctly managed in the recovery.

There is some uncertainty on these forums as to what/when triggered the pitch up. The A/P kicked off due to overspeed in clear-air turbulence - pitch up seems more likely due to protection against overspeed than the stated "corrected or phase-advanced angle of attack" "excursion beyond alpha prot"?

Last edited by sensor_validation; 31st May 2011 at 10:31.
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Old 31st May 2011, 08:41
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He must have asked and they will have explained ...

@NWR

Thanks for the Tarom ROT381 video link.

The BEA incident report (24 September 1994) makes for an interesting comparison with the current discussion.

http://www.bea.aero/docspa/1994/yr-a...r-a940924a.pdf

Of particular interest are the crew comments, CVR readout (p12-13), and the analysis, sections; Incident Sequence, Analysis of the Stall Protection Logic, and Conclusions (p26-34).
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Old 31st May 2011, 08:44
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FPV

Originally Posted by fizz57
Just a general thought - does the Flight Path Vector display use air data at all or is it just inertial? Would this have helped the pilots' SA in this situation?
ACARS messages tell that the FPV (bird) has been selected, but the bird on both PFDs disappeared.
  • Was it available at all, initially ?
  • Was it followed ?
  • Was it reliable ?

BEA, the data ...
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Old 31st May 2011, 09:05
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RealQuax

The Tim Vasquez profile chart is probably as good as it will get. At this time we don't know if the aircraft had deviated clear of the main Cb cells, but its position along the track was a little different than that portrayed in the original chart. The whole ACARS sequence took place in the arrowhead centered on 3N and the time at 3N was 02:10:30z (or thereabouts).
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Old 31st May 2011, 09:17
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Originally Posted by mm43
...
The AoA vane plus IAS provides the stall warning. Only problem is that the IAS must be greater than 60KTS for the combo to provide the SW. The SW stopped because the IAS had dropped too low, and when they attempted nose-down and got an IAS over 60KTS, the SW started again. ...
That 60 kts again --- why would a blocked pitot and open drain stick at this value? It seems to me that the IAS system outputs 60 kts (or is it 60.001?) when UAS detected, so that protections/warnings that are disabled at low speed are not disabled with UAS.

So if there's any airspeed indicated above or below precisely 60kts its a real live reading, (and if 2 out of 3 agree it is validated and used in protections/warnings) - is this documented?

You can build AoA indicators with pitot style pressure measurements using the fact that the pitot under-reads when not pointing directly into the air-stream, but it must need careful calibration - if simply varying as the cosine of the AoA AF447 would have been indicating nearer 100kts during the descent?
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Old 31st May 2011, 09:28
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sensor_validation

Thanks for that. I must try to keep up!
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Old 31st May 2011, 09:36
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What puzzles me is the idling of engines (not just thrust reduction: IDLING)

When was it commanded? (At least 2min26sec before impact ?) Who commanded it? believing to be overspeeding, or as a resort to recover a stall that wasnt expected to recover just by sidestick pitch-down commands?

It would have been bettter to release nothing for the shake of releasing a comprehensive interim report, that releasing latest BEA may27th report, where it is quite obvious that they purposedly censor very relevant information that they surely hold!
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Old 31st May 2011, 10:51
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sensor-validation;

IAS reflects the difference between pitot pressure and static pressure. Both sources are 'disturbed' at extreme angles of AoA and sideslip. I wonder if BEA has taken possible static source errors into account when quoting altitudes. These should be checked with IRS and/or GPS data.
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Old 31st May 2011, 11:40
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Originally Posted by HazelNuts39
sensor-validation;

IAS reflects the difference between pitot pressure and static pressure. Both sources are 'disturbed' at extreme angles of AoA and sideslip. I wonder if BEA has taken possible static source errors into account when quoting altitudes. These should be checked with IRS and/or GPS data.
@10,000 ft/min I don't think any correction to text required! But sure any indication will be unsteady and oscillating depending on which port in use pointing which way and how in detail they are combined/ filtered. Google finds this schematic from globalsim.web:-

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Old 31st May 2011, 12:23
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Pitot tubes

Machinbird: Only problem with this concept is that what happens to the water droplets that inertially fly through the outflowing air at the pitot inlet and accumulate.
The pump control will increase the inside P to maintain the target air flow, therefore water will eventually be pushed out. If this is a transient situation the apparent IAS spike could be filtered by software.

If it would last longer then the pump control would reach its max value w/o generating the target air flow, and the logic would send a "pitot clogged" signal instead of delivering an erroneous speed value. Hopefully one or two of the other tubes would still work.
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Old 31st May 2011, 12:55
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I have been reading through this long thread. Very interesting discussion.

What always was omitted and this is something I am unsure what happened and maybe someone can recall this.

The AP disconnected automatically, but what happened before? What actually made the AP disconnect.

If we go back in history, and I am still not certain what this fact is trying to tell us, please let me tell you this.

I plotted the position of the wreck and the position where the Tail was found. The Tail actually was found 70Km northeast of the location of the wreck. While the sea current where at that day were going northeast to south. How the heck did the Tail get so far away from the wreck assuming that it was still sitting on the tailcone on impact.

Second thing that makes me a bit confused. The 36G arm in the rudder of the recovered tail, was actually found broken. Please keep in min that the 36G arm is not the fixation on the aircraft but the hinge between tail and rudder. This special arm can withstand 210'000 nm of force. The tail cone would have acted as buffer between the tail and the aircraft body. Due to this I cannot think that there was enough force to break it.

Bringing these two elements together makes me assume that the tail was already ripped of the plane earlier. While in deepstall? No. But at what point in time. Maybe exactly at the point when the pilots were doing a right turn. Remember, the FDR said, pilot gave stick input to the left and up. At the same time, ACARS reports a failure of the RTLU. Well, I would say, tail gone, RTLU gone. Logical response of ACARS to report it as failed

As BAE has not release exact coordinates of the flightpath, it makes it hard to overlay with the other position. fact is, they turned back before the decent and due to this the theory looks valid to me.

Opinions?
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