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Air France jet missing over the Atlantic

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Member
Registered: May 2009
Posts: 414
Location: Mumbai, India
Jeroen D wrote
.. it appears that the authorities are now considering it might be a terrorist attack after all. They base this on the very large area in which debris seems to have come down, and large patches of unburned fuel found on the ocean.


Jeroen


I don't understand. How do these factors point to a terrorist attack ?
Member
Registered: May 2009
Posts: 414
Location: Mumbai, India
Peter Lang wrote
What still confuses me is, that the debris they found is far south of the last report on the south side of the thunderstorm. The aircraft was northbound and about to leave the storm cell.


Today the german Spiegel ...says, the debris found is not from the missing Air France A 330. They had no wooden pallets on board.

Peter


Which makes me wonder, could it have been a mid-air collision ? And the debris is from the other aircraft? This might answer both of Peter's points.

Of course, this would mean that there would be two planes reported missing ...
unless ...
Member
Registered: May 2009
Posts: 269
Location: between EDDF and EDDN
Hi Shiv,

Yes and also the debris of both aircraft should be within a relative clear range.

A mid air collision occured several years ago, at the african coast with a German and an US military aircraft. What I remember is this: they said the weather satellites noticed a light flash of that explosion.

Perhaps this time a possible explosion (if there was one) could not be seen by satellites due to the heavy thunderstorm and lightnings around.

The problem now is we have very sparse facts:

- Crew did not send emergency calls.
- Automatic generated failure reports of aircraft systems.
- Other crew saw orange parts on the water surface which they could not identify
- Other crew reported white flash of light going down, no lighning (meteorite?)
- Other crews reported weather not worse than usual.
- Debris found far away from last automatic system report (which probably also transmitted the position) almost in opposite direction of their flight path.
- Debris turns out not to be from the missing plane.

I have to admit, that this informations leave a lot of questions and some space for speculation and conspiracy theories. But this seems not to be very useful. It does not clarify or solve anything. It only feeds emotions.

Hope they find the parts, we all want for an answer.

Peter
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Location: KTMB
More noises about failing airspeed indicators pop up, and reports about having received not less than 24 failure messages before everything stopped. Apparently the A/P was not engaged at the final failure moment.
Member
Registered: Jun 2009
Posts: 138
Location: Melton Mowbray. U.K.
Jeroen Hoppenbrouwers wrote
There is, they do. It is called ACARS.

Now, truly, it isn't ACARS as that is the transport network used to relay the messages. ....


So I don't want to appear stupid (that would be first!)

But would the ACARS message/ Do the ACARS messages always include a GPS position in the message, regardless of the nature of the message that is transmitting?

Thanks

Carl

edit: sorry I am being stupid - I see on AVHerald on the picture it does say Last ACARS position report.
Member
Registered: May 2009
Posts: 958
Location: Chicago
Assuming that we're moving closer to the day when bandwidth isn't an issue, why not send as much information as possible back home? You could basically create an off-site backup of the plane's black box back home in Toulouse or Seattle.

Will
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Bandwidth isn't an issue if you have copper or glass fibre lines, or nearby high-frequency network towers. In the middle of the Atlantic, bandwidth is surprisingly scarce. Satellite links can carry a lot, but each plane needs to share in the link capacity.

What probably is possible is to not have a continuous open channel with bulk data, but to allow for sudden data bursts the moment something breaks. Such a system would not catch a midair collision or explosion, but it could help with the reconstruction of a chain of events.
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CarlBB wrote
But would the ACARS message/ Do the ACARS messages always include a GPS position in the message, regardless of the nature of the message that is transmitting?

Not all, but the cost of doing that would be relatively low (just a few bytes). Don't forget that ACARS itself does not include many message format/content guidelines. It's nearly all up to the airlines themselves. Many will have included these position reports.

What is "an ACARS position report" in the Air France case is not clear. There are ATC-over-ACARS systems in regular use, but they are not necessarily continuous.
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Location: KTMB
I'm now reading reports that they picked up two bodies and material that could be nearly impossible NOT to come from the Airbus.
Member
Registered: May 2009
Posts: 146
Quote
Apparently the A/P was not engaged at the final failure moment.


If this turns out to be another one of the A340 inflight autopilot upsets, then Airbus could be in for a massive lawsuit !

I believe the other incidents happened in good vis and daylight, maybe if it happened at night in a thunderstorm it was a different story :(
Member
Registered: May 2009
Posts: 269
Location: between EDDF and EDDN
I read in some german news, that Airbus adviced Air France to change the pitot tubes. But AF only did change the change those from A320 series.

Another interesting article In found here (also in german):
http://www.welt.de/vermischtes/article3853525/Experte-beklagt-absurde-Zustaende-im-Cockpit.html

Here it is said, that 2001 an A 330 ran out of fuel, due to a detached fuel pipe. They lost their complete fuel in 13 minutes. After this both engines failed and the A 330 glided within 19 minutes into the azores and could land safely.

Experts have been very frustrated that they could not find any records for 21 minutes on the flight data recorder. The electrical power also failed.

What would have happenend, if the azores did not come across incidentally?

Peter
Member
Registered: May 2009
Posts: 944
Peter Lang wrote
I read in some german news, that Airbus adviced Air France to change the pitot tubes. But AF only did change the change those from A320 series.

Another interesting article In found here (also in german):
http://www.welt.de/vermischtes/article3853525/Experte-beklagt-absurde-Zustaende-im-Cockpit.html

Here it is said, that 2001 an A 330 ran out of fuel, due to a detached fuel pipe. They lost their complete fuel in 13 minutes. After this both engines failed and the A 330 glided within 19 minutes into the azores and could land safely.

Experts have been very frustrated that they could not find any records for 21 minutes on the flight data recorder. The electrical power also failed.

What would have happenend, if the azores did not come across incidentally?

Peter


Another update, supporting your post:

http://online.wsj.com/article/SB124428319732091447.html#printMode

Excerpt:

"Lost Plane Was Due for Change of Speed Sensors"

<snip>

"Air France said in a statement Saturday that starting in May 2008, some of its A330s and similar A340 models "experienced incidents involving a loss of airspeed data" while cruising at high altitude. Air France and Airbus concluded the problems arose because the probes briefly iced-over, the airline said."

"The airline said it had begun replacing the units on the Airbus models in April, following tests indicating that a newer-model sensors would give fewer faulty airspeed readings at high altitude due to icing. Air France said it has now accelerated the replacement program and also reminded its pilots how to handle a loss of airspeed data."
_______________
Best wishes,

Phil Bunch
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Location: KTMB
Somebody somewhere will now be thinking about a system that detects gross changes in indicated airspeed that do not match up with what the IRU says, and tries to work out a method to detect faulty pitot tube indications without endangering the stall warning system too much.
Member
Registered: May 2009
Posts: 269
Location: between EDDF and EDDN
Phil Bunch wrote
Air France said it has now accelerated the replacement program and also reminded its pilots how to handle a loss of airspeed data."


A question is in my mind since some days. We live in a time of INS and GPS. It should be possible to get altitude and groundspeed data from this. (Even the GPS in the cars can show groundspeed) The winds are also known. So why do all airspeed issues depend only from the pitot tubes? Ok, the pitot tubes are rather reliable, have haeting systems and are common use. But for safety or backup reasons it should be possible to get rather reliable data in case of pitot tube failure, at least to bring an airplane safely to an alternate. Especially at night time, where there is no visual reference.

It is not acceptable that computers get scared, when they have to handle different airspeed indications.

Just some thoughts
Peter
Member
Registered: May 2009
Posts: 125
Quote
The winds are also known.


How?
Member
Registered: Jun 2009
Posts: 20
Peter Lang wrote
It is not acceptable that computers get scared, when they have to handle different airspeed indications.


I agree, It is very difficult to get programmers to screen input data for errors such as impossibly rapid changes or to resolve conflicting data without producing undesirable outputs. Programers often miss screening out data format problems such as text data where numeric should be. Format screening should be mandatory in any software project but I've found it missing in even high reliability code!

I have 2 questions.

1. Dose anybody have the complete ACARS data steam annotated with time and plane text descriptors? Some of the media seam to have it.

2. The cabin pressure alarm was described as "Cabin Rate" out of spec and could be triggered by fast pressure decreases or increases. Is it possible to trigger the cabin rate warning by a steep dive with the pressurization working normally?


[JH: edited the word "pressure" for funny spelling error]
« Last edit by Jeroen Hoppenbrouwers on Mon, 08 Jun 2009 04:51:35 +0000. »
Moderator
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It is not just programmers that often don't screen everything.

The issue with software development is that if you do not trust your input data, you have to write programs that are 90% paranoid checking of everything, and 10% getting work done. If your company or manager is under pressure to deliver a complex system in time and on budget, and you have to struggle to meet the specs of 10% of the code, why spending nine times more on checking that "should never be necessary"?

Of course it should happen, but the question is whether it is affordable. In aviation and other safety-critical software, there already is much more paranoia going on than elsewhere, but there is always a statistical and economical limit.


Jeroen
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Posts: 269
Location: between EDDF and EDDN
Member
Registered: Jun 2009
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Jeroen Hoppenbrouwers wrote
It is not just programmers that often don't screen everything.

Of course it should happen, but the question is whether it is affordable. In aviation and other safety-critical software, there already is much more paranoia going on than elsewhere, but there is always a statistical and economical limit.


Jeroen, I agree, lots of things don't get checked during design, but the trick is to limit the system's reactions to failures and unanticipated events too something that can be worked with. Back in the days of analog electronics, data inputs were bandwidth and range restricted to limit the effect up stream failures had even-though this significantly increased the size and weight of the circuitry.

Affordability is an interesting and difficult problem. Most of my experience is with spacecraft, the combined cost of the spacecraft and launch vehicle often are in the 100 to 200 million dollar range. Operating cost for 10 or 20 years can double overall program cost. I'm not sure of the cost of a new A330 but it's probably close to 100 million but this pails in-comparison to the liability that a crash can incur, approaching 1 Billion, ($1,000,000.)

In a well organized software development program, basic input and consistency checking is very cheep and can be built into the software development environment software. As proof: the ACARS system had no problem detecting the inconsistent airspeed data. The very procedure that Airbus recommends the pilots use to correct for a failed airspeed indication can be directly implemented in software to at least keep the aircraft stable until a definitive resolution is made by the pilots. As designers, maintainers and users of high-tech systems we should not except that exhaustive checking of simple routine things is too expensive, the computers we use to design them are very good at ensuring that routine checks are performed as long as you implement a well thought-out policy at the beginning of a program.


It's beginning to look like they entered and were unable to recover from a Hi altitude stall. If the pilots were not able to determine correct airspeed stall recovery could be impossible. Imagine having an overspeed stall when you think you are flying too slow! You keep the nose down and apply power, the situation rapidly gets worse. Or an underspeed stall when airspeed looks OK. With the turbulence of the storm, mild disorientation from the storm or the aircraft CG off centerline, the aircraft could easily end up on it's back witch is nearly unrecoverable with even good wether and a good aircraft. (No Failures) This is why I'm looking for the timeline and details of the pressure warning, these will quickly narrow the range of possibilities.
Member
Registered: May 2009
Posts: 146
A Bit more information about Black Boxes as discussed in the first part of the thread.

http://www.boreme.com/boreme/funny-2009/flight-box-recorders-p1.php

Cheers PC
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Member
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http://online.wsj.com/article/SB124428319732091447.html#printMode

The above URL is the latest updated WSJ news story on the crash with some new details, etc.

A quote from the article follows:

"Modern jetliners have backup speed-measuring systems and pilots train for such situations, so damaged probes, by themselves, should not cause a plane to crash, industry officials say."

Is this true as a general statement for trans-oceanic airliners? I thought there were no backup air speed subsystems except for multiple pitot tubes and their associated components. Also,I thought that one's only indication of an air speed accuracy problem in the dark over an ocean at cruise altitude would be something like "air speed indicators disagree", or perhaps a grossly impossible speed indication, along with some alarms and error condition messages on the cockpit displays.

Finally, my aging memory tells me that the speed difference between nice stable cruise and a stall at cruise altitude is relatively small. Is this qualitatively correct? If so, then accurate air speed at cruise takes on special importance, of course. It wouldn't be enough to be "sort of working" or "working but with substantially reduced accuracy".

Along this line of thought, I recall an incident in which an Air China crew more or less dozed off during cruise and failed to notice that an engine of their 747 had stopped making much thrust (perhaps it completely stopped - can't recall). As a result, the other 3 engines and the autopilot tried to hold the requested cruise altitude as long as possible, but the airliner ultimately stalled out and went into a high-speed dive, finally waking up the crew. They managed to rescue the diving, possibly supersonic aircraft before it hit the ocean, but considerable damage was done to the aircraft by excessive airspeed and mechanical stresses as I vaguely recall. Fortunately, it was able to fly to the San Francisco airport destination. I think "Captain Tarmack" described this incident in one of his columns or online forum posts.

With their vulnerability to everything from icing to insects to protective tape covers being left on the pitot tube ports, one would like to have a backup system such as GPS-based speed available to the crew. This wishful thinking of course would only make sense if it is airworthy in a formal, strict sense through rigorous engineering analysis and testing, none of which I can contribute to even for informal discussion purposes.
_______________
Best wishes,

Phil Bunch
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Location: KTMB
If you max out your cruise altitude, you indeed are left with about 10 knots between overspeed buffet and stall speed. On the 744, the red/yellow bands would nearly touch.

This is one of the reasons that in case of expected or experienced turbulence, you should not be near your maximum altitude. One wind gust and off you go.

Air speed or Mach here is the absolute key. GPS or IRS speed does not tell you anything as your wings don't care at all about anything but (indicated) air speed/Mach. In stable conditions away from the Coffin Corner you may be able to fall back onto ground speed, but at the edge of the envelope it's useless.
Member
Registered: May 2009
Posts: 125
Quote
"Modern jetliners have backup speed-measuring systems and pilots train for such situations, so damaged probes, by themselves, should not cause a plane to crash, industry officials say."


They are probably talking about Standby Instruments (although these sometimes use the same pitot/static sensors). AOA & thrust coupling is another possibility for maintaining airspeed, but I get the impression that pilots don't often get the opportunity to practise this kind of thing.
There have been lots of instances where pilots haven't been able to identify the faulty component/s, so they use the wrong instruments.

Most aircraft these days have groundspeed displays based on IRS or GPS, but as Jeroen says, they don't tell you what your airspeed is.
Member
Registered: Jun 2009
Posts: 20
To understand how air data can be so disastrously wrong, one has to know why it is important and how the instruments work. I'll try to give a brief discussion of each, but brief is not easy.

Air speed is critical to most phases of flight. Take off rotation occurs just before stall speed. Best performance climb out occurs just above stall speed. G forces wile turning at lower speeds require nearly stall lift from the wings. High altitude flight is conducted in what is called the coffin corner of the flight envelope. Here stall speed increases due to the thinning air to nearly the speed of sound. Turns at high altitude increase the wing loading when there is little margin for increase. The only 2 phases of flight you don't need to worry about air speed are (1) mid altitude moderate speed straight and level flight and (2) parked on the tarmac.

Air speed can only be computed from measurements of the air being flown through. From memory, air data systems can provide 4 measurements of use to the pilot, barometric altitude, air speed, stall warning and angle of attack. Please let me know of I missed any. Most air data measurements are dependent on an accurate determination of the static (non-moving) pressure of the air the plane is flying through and is supplied by a static source.

The simplest static source is holes on the sides of the pitot tube that are perpendicular to the airflow. Clearly a pitot tube static source can be corrupted by the same problems as the pitot dynamic pressure (air speed), such as ice, blocked lines, insects and being covered. On most aircraft, If the static sources are corrupted, all the air data information is wrong. A few types of aircraft, use different forms of static sources and air data ports, such as carefully placed holes in the aircraft skin. These systems have to be carefully calibrated in flight test and are even more sensitive to contamination than pitot tubes. They are used mostly on military planes that have problems with pitot tubes, such as supersonic flight and stealth.

Barometric Altitude is the most fundamental air data presented to the pilot in the form of the altimeter. Barometric altitude is calculated by subtracting the static pressure from a reference pressure and multiplying by a constant to convert the pressure difference to feet of altitude. At low altitude, the reference pressure is the barometric pressure at the airport of interest. Taking off, the reference is set by adjusting the altimeter to the actual elevation of the runway. Landing, the pilot has to obtain a barometric pressure measured on the ground and manually input that pressure into the altimeter.

The Blue Angels once crashed four or five planes at once because they violated their air-show barometric altitude procedure. The acrobatic procedures are written in altitude above ground level (AGL) so the procedure dose not need to be rewritten (and relearned) for each airport. But this requires that the altimeter be set to sea level before takeoff. Most of their practices and air-shows are at airports close to sea level making altitude above sea level (ASL) and AGL nearly identical. Before takeoff, they set the altimeters to the altitude of the runway as you would for a normal flight instead of sea-level. Apparently this group of pilots had been making this mistake for sometime and got away with it because the error was less than the built in safety margin. They did a loop, and toped out 1000 feet to low because the ground was 1000 feet higher normal.

For high altitude flight the altimeter is set to "standard pressure" so that all aircraft will fly at the same altitude when commanded to a specific flight level. The actual distance above the ground of a specific flight level varies by several hundred feet with the wether from day to day but also is different at different places at the same time.

Air speed is calculated by subtracting the static pleasure from the pitot dynamic pressure then converting to velocity. Air speed is fundamental for nearly all phases of flight and most critical at landing and high altitudes. Before GPS and other radio navigation adds it was necessary to guess what the winds were to estimate ground speed for navigation. A friend was taking flying lessons and the instructor asked him what he thought their ground speed was. He knew the air speed was 75 knots and they had a 15 knot head wind at takeoff. Thinking the wind would be higher at 3000 feet he said 50 guessing the wind was 25. The instructor said, "Look down out the side window." They were over the Chesapeake bay bridge going backwards! The head wind was about 100 knots. The plane could not fly faster so they had to fly at low level to find lower winds to get back to the airport.

Stall warning is determined by a stall warning pitot that faces backwards on the upper rear wing surface. It looks for air recirculating (moving forward) over the wing as the stall vortex begins. It may use the primary static source or use it's own static source. At low speeds it measures the velocity the air is moving over the wing and produces the stall warning when the air flow reverses (moves forward) impinging on the dynamic port of the probe changing the dynamic pressure from lower than to higher than the static pressure. On most small planes air moves from the dynamic port through a reed buzzer and out the static port. The sound gets louder and higher pitched as the stall deepens. This systems requires a dedicated static source as the volume of airflow through the buzzer would corrupt the static reference for other uses. At high altitudes the calibration of the stall warning may need to be changed and could be different for both overspeed and underspeed. In high altitude stalls, the air flow still separates form the wing causing reduced lift, but the flow direction may not change. I don't know how stall warning is implemented on large jets and is probably dependent on the aerodynamics of the particular wing design. More information is welcome.

Angle of Attack (AOA) is not normally displayed to the pilot even in aircraft that are equipped with it. Test pilots who have used AOA love it and want it an all aircraft. It provides a better indication of stall than traditional stall warning, and can be useful in other phases of flight. Again, the stall AOA may be different for high altitude stalls than low altitude. The beauty of AOA is that stall is always at the same AOL regardless of airspeed, weight, air density or other variables. Angle of attack can be used as a proxy for air speed as the relationship with airspeed and weight is constant. The simplest way to measure angle of attack is with a horizontal wind vain in the airflow. But the sensor must be held a considerable distance from the airframe to get clean air and is thus not practical for operational aircraft. All modern flight control systems compute angle of attack (because it is such a good measure of performance) form traditional air data sources. So, if the air speed is corrupted so is the AOA computed from the same air data sources.


Other methods of determining airspeed. I can can only think of 2 that will work, Doppler radar and acoustic distance measurement. There may be one or two other methods but not many more.

Acoustic distance measurement. It is not obvious why this works, but it does. By placing acoustic transducers across a horizontal space open to air flow continuous measurements of the distance can be made. (Say between two engines). When stopped all this tells you is the distance between the engines, but when the air is moving relative to the plane, the air pushes the sound waves rearward relative to the aircraft. To be picked up by the receiving transducer the sound has to travel diagonally relative to the still air. This diagonal motion increases both the time and distance the sound travels between the two transducers (the receiving transducer has moved forward during the transit time of the sound.) This method works well and is in use for measuring fluid flows in pipes and ducts. A horizontal gap should work on aircraft up too about Mac 0.95. Reconfiguring to a longitudinal (length wise) gap will produce 2 different measurements, 1 for forward and 1 for rearward. Producing 2 different times for the same pair of transducers provides a nice consistency check. As speed increases, the forward measurement will take longer and signal strength will be reduced. But the rearward measurement will take less time and increase the signal strength as speed increases, taking 1/2 as long at the speed of sound.

Doppler radar. This method should already be available from Doppler wether radars all ready on the marked. Doppler radar not only measures the strength of reflected radar energy from rain and ice it also measures the velocity that the particles are moving relative to the aircraft by measuring the shift in frequency of the reflected energy. This is the same method used by police radar for traffic speed. In police moving radar (in car), the receiver uses the return energy from the stationary ground to calculate the speed the radar is moving and uses that speed to calculate the ground speed of other vehicles. Airborne Doppler wether radar has to do the same thing, measure the frequency of the ground return to determine the aircraft ground speed. The frequency shift of the wether return is the relative difference in wind speed and aircraft speed so the aircraft ground speed must be subtracted to produce a usable wind ground speed wether map. The raw wether return frequency shift is the airspeed of the aircraft when the return is from air immediately in-front of the plane. The raw relative speed map shows what the airspeed will be when the aircraft arrives at a particular point if current conditions persist. This is the only technology currently available that can give a true airspeed without using air pressure ports. The angle of attack can be read directly from the radar by looking for the angle of maximum airspeed.

A 3D Doppler Radar is capable of providing nearly all the information that aircrews use to fly. It can produce air speed, and AOA. The combination of air speed and AOA provides stall warning. The ground return provides altitude above ground level (AGL), rather than barometric altitude, also it is the AGL in-front of the aircraft, rather than under it. But when landing, this will produce the altitude above the runway, a more useable reading than above sea level.

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