Air France Jet Crash: Are Commercial Jets Safe Against Lightning?

In summary, the conversation revolved around the Air France jet that crashed in the Atlantic and the speculation that lightning may have been the cause. It was mentioned that lightning strikes on commercial jets are not uncommon and that they are designed to withstand them, but there is still a risk of structural damage and electromagnetic interference. There were also discussions about the accuracy of models for predicting damage from lightning strikes and the difficulty of locating the plane in the vast ocean. Some debris has been found, but it is still uncertain if it is from the crashed plane. There was also speculation that the lightning may have caused electrical problems on the plane, leading to its crash. Overall, more research and investigation is needed to determine the exact cause of the crash.
  • #71
Been following this here

http://www.pprune.org/rumours-news/376433-af447-6.html

Fair bit of fact, good read.

Most speculation at the moment as any number, or any single thing could have caused this.

There has been no confirmed wreckage found, its all floating junk that's always in the atlantic so far.

One can refer back to the near miss with the QF A330 flight not too long ago, such a failure combined with bad weather, lossing WX and flying into the heart of a CB could have brought this plane down.
 
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  • #72
herpamad said:
There has been no confirmed wreckage found, its all floating junk that's always in the atlantic so far.
Then there are conflicting reports. Some news articles are stating that some pieces of debris are confirmed to be from the Air France flight.
 
  • #73
Air France memo says it's replacing flight sensors
http://news.yahoo.com/s/ap/20090605/ap_on_re_la_am_ca/brazil_plane

Apparently there is concern that the pitot tubes iced up, and provided false information to the flight deck.
RECIFE, Brazil – An Air France memo to its pilots about the crash of Flight 447 says the airline is replacing flight-speed sensors in all its medium- and long-haul Airbus jets.

Air France declines to comment on the memo obtained by The Associated Press, saying it is for pilots only.

Airbus says the matter is part of the probe into the crash that killed 228 people flying from Rio de Janeiro to Paris.

The memo sent Friday says Air France has been replacing instruments known as pitot tubes and will finish in "coming weeks." It does not say when it started.

One theory of the crash is that the tubes feeding speed sensors may have iced over, confusing plane computers and causing the plane to fly too fast or slow in rough weather.

. . . .
 
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  • #74
One theory of the crash is that the tubes feeding speed sensors may have iced over, confusing plane computers and causing the plane to fly too fast or slow in rough weather.
All Pitot tubes have heaters. There was a spectacular crash of a stealth bomber on takeoff who forgot to turn the heater on (no idea why this should even be an option), there have also been a couple of crashes where tape was left over them after cleaning or a bird had stored nuts in the hole!

It's possible that the heaters failed or that icing was so bad it overcame them but the aircraft has multiple independant ASIs
 
  • #75
French nuclear sub was directed to the area.
 
  • #76
From the activities of Air France we might assume that either Airbus, Air France or both are concerned about possible pitot tube mis-performance--or clever misdirection, but people don't conspire, so nevermind that--however people do act in common cause :-p

http://www.auf.asn.au/groundschool/umodule2.html

(*The reason why CAS [calculated air speed] does not always correlate to aoa [angle of attack] is that when inertia and random displacement forces — atmospheric turbulence — come into play, aoa may change momentarily without a change in CAS.)

An ASI [air speed indicator] is an imperfect mechanical instrument which is subject to instrument errors. The associated pitot/static system is also prone to pressure sensing errors due to the positioning of the pitot head and the static vent relative to the airstream. That relative position changes as aoa changes. CAS is the airspeed after you have applied corrections to the IAS [international standard atmosphere] for those instrument and position errors occurring at that aoa in that particular aircraft. The measured corrections should be stated on a card placed near the ASI. You should also be aware that position errors may be quite significant, possibly 10 knots or so — particularly at high aoa or when the aircraft is slipping.

(My boldface and bracketed text.)
 
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  • #77
The problem with calculating airspeed is conflicting estimates. Available to the flight instuments are the the pressure reported by the pitot tubes, the vertical airspeed reported by variometers, angle of attack reported by the angle-of-attack sensors located on the leading edges of the wings, and the atitude and velocity reported by the inertial reference unit. This is agrevated by the possibility of failing instuments. On top of this there are distrubuted sensors on each wing.

Airbus has the algorithms in hand. They have the software, but not the hardware. They want the instuments in hand to see if they are damaged in any way. They can't obtain these from Air France 447, but they can examine samples from the fleet of Air France airliners. Air France has a monitary interest in reporting good news to their potential customers. Supplying pitot tube modules to Airbus for analysis should be in their best monitary interest. It is good for both parties should they be able to report: "problem solved". Corporate grubbers, you know, regardless of reality, if a happy ending in air saftey can stick in the public craw, go for it.
 
  • #78
Phrak said:
The problem with calculating airspeed is conflicting estimates. Available to the flight instuments are the the pressure reported by the pitot tubes, the vertical airspeed reported by variometers, angle of attack reported by the angle-of-attack sensors located on the leading edges of the wings, and the atitude and velocity reported by the inertial reference unit.
Why would these result in conflicting information? They don't measure the same thing. The only thing that measures airspeed is the pitostatic tube.
 
  • #79
russ_watters said:
Why would these result in conflicting information? They don't measure the same thing. The only thing that measures airspeed is the pitostatic tube.

There are several pitot tubes, each measuring/reporting different values. The pressure presented to the transducer in a pitot tube depends on on the air density as obtained from barometers or calculated from the inerital reference unit, and the direction of the airflow on both pitot head and the static vent.

The nominal airflow direction can be calculated from the inertial reference units (that calculate acceleration, velocity, displacement in space, and orientation with respect to a calculated horizon), angle of attack sensors, and variometers (for vertical airspeed).

To this, add GPS altitude data.
 
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  • #80
Phrak said:
There are several pitot tubes, each measuring/reporting different values.
Well, if one is damaged or coverd with ice, sure, but I would think the plane has the ability to compare and detect faults.
The pressure presented to the transducer in a pitot tube depends on on the air density as obtained from barometers or calculated from the inerital reference unit...
Yes, pressure depends on air density, but the critical "airspeed" for an airplane is indicated (uncorrected) airspeed. It doesn't then get corrected for local air density, because indicated airspeed, is what determines how much lift the wings produce. You wouldn't want it corrected, otherwise, you might find (for example) the plane would stall even though its equivalent airspeed (corrected for density) is well above stall speed.
...and the direction of the airflow on both pitot head and the static vent.
No, the pitostatic tube is mounted on its own little wing that ensures it is oriented with the correct angle of attack.

http://en.wikipedia.org/wiki/Airspeed

The nominal airflow direction can be calculated from the inertial reference units (that calculate acceleration, velocity, displacement in space, and orientation with respect to a calculated horizon), angle of attack sensors, and variometers (for vertical airspeed).

To this, add GPS altitude data.
No, they can't. The direction/speed of airflow can only be directly measured by the pitostatic tube. Those other sensors only tell you which way they plane is moving with respect to the earth. The key difference is they don't take into account wind. There is no conflict between these information sources because those other information sources aren't used in the way you are suggesting.
 
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  • #81
I don't know where to start. The pitot tubes don't measure wind direction. They do not read the same values under dynamic conditions, especially turbulence. There are triple redundant systems and algorithms at work. The flowchart for all these quickly grows into megabytes of code to consider the multiplicity of conditions from failures and faults.
 
  • #82
russ_watters said:
Well, if one is damaged or coverd with ice, sure, but I would think the plane has the ability to compare and detect faults.
Don't remember which one but I think one of the 757/767? crashes in S America was caused by a single blocked pitot tube, the crew saw conflicting readings but didn't know that the autopilot only took ata from one tube - unfortuantely in this case the blocked one.

Airbus issued an advisory basically just saying pay attention if you are in bad weather and the instruments give different readings.

It would be nice to have a way of measuring local airspeed that wasn't quite so dependant on the air conditions around the aircraft - but that might be a bit of a paradox!
 
  • #83
Phrak said:
I don't know where to start. The pitot tubes don't measure wind direction.
Have a look at the picture in the wiki. Notice that it is mounte on its own little wing on a swivel so it always points into the wind (at least in the pitch axis).
They do not read the same values under dynamic conditions, especially turbulence. There are triple redundant systems and algorithms at work. The flowchart for all these quickly grows into megabytes of code to consider the multiplicity of conditions from failures and faults.
I'm not sure what you are getting at here. What you seemed to be saying before is that if the pitostatic tube on its attitude swivel says the plane is flying at 200 kts with a 5 degree angle of attack but the gps says it is moving across the ground at 150 kts that that is a conflict that could be a problem in maintaining control of the plane. It isn't - that's a navigation problem (not a flight control problem) only.
 
  • #84
Have a look at the picture in the wiki. Notice that it is mounte on its own little wing on a swivel so it always points into the wind (at least in the pitch axis).

The wikipedia picture was not the best example of a pitot tube.
The picture in wiki is a pitot tube with an angle of attack sensor (the black "little wing" ) attached. The angle of attack sensor is a completely separate instrument and is only attached to the pitot tube (in that example) as a convenience for mounting.
 
  • #85
jgrenwod99 said:
Have a look at the picture in the wiki. Notice that it is mounte on its own little wing on a swivel so it always points into the wind (at least in the pitch axis).

The wikipedia picture was not the best example of a pitot tube.
The picture in wiki is a pitot tube with an angle of attack sensor (the black "little wing" ) attached. The angle of attack sensor is a completely separate instrument and is only attached to the pitot tube (in that example) as a convenience for mounting.
In the picture, though, it makes the pitot tube swivel to ensure that it points in the direction the plane is moving. They aren't separate devices.
 
  • #86
An airplane always moves forward (like an arrow) so the pitot tube is mounted so it points in a forward direction. Pitot tubes don't swivel. You may be assuming that the black disc at the base of the pitot tube mast swivels in some way, but it doesn't. What is movable on the pictured device is the black wedge shaped piece which is the angle of attack vane.
 
  • #87
I worked for an airline for ~10 years. Lightning strikes were common. Only once did I see an aircraft sustain actual damage from a lightning strike. It was a Dornier 328. A large chunk of the verical stabilizer was blown off at the tip. The fuselage was damaged along the entire length. It looked as if it had been hit with a spot welder. There were several holes in the aluminum, the largest about the size of a dime.

I've only ever seen fixed pitot tubes. Angle of attack sensors (obviously) swivel. In the wiki picture, the actual pitot tube (silver) is fixed.
 
  • #88
NateB said:
I've only ever seen fixed pitot tubes. Angle of attack sensors (obviously) swivel. In the wiki picture, the actual pitot tube (silver) is fixed.
Looks to me like it is part of the swivel, but if most are fixed, ok...
 
  • #89
Air France tail found; US helps hunt black boxes
http://news.yahoo.com/s/ap/brazil_plane

So hopefully they will recover the black boxes, as well as more of the craft, and well learn more details.
 
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  • #90
russ_watters said:
Have a look at the picture in the wiki. Notice that it is mounte on its own little wing on a swivel so it always points into the wind (at least in the pitch axis). I'm not sure what you are getting at here. What you seemed to be saying before is that if the pitostatic tube on its attitude swivel says the plane is flying at 200 kts with a 5 degree angle of attack but the gps says it is moving across the ground at 150 kts that that is a conflict that could be a problem in maintaining control of the plane. It isn't - that's a navigation problem (not a flight control problem) only.

I'm sure you're right. I'm sure the Airbus must use vaned pitot tubes. Three pieces of air data can be used to obtain corrected speed: the dynamic and static pressures, and angle of attack for off-axis corection--or the tubes might handle this on their own. The swivel is useful in negating the need for off-axis airflow around a verticle axis. I don't think yaw information is collected. I'll find out.
 
  • #91
Additionally, angular correction factors for the barometric pressure can be input to the ADIRU to quantify side slip. You would want this information because the area of the pitot tube normal to the airflow is proportional to cos theta. Pitot tubes can have static pressure inlets on horizontally disposed sides of the tube. The difference in measured barometric pressure between these two can be used to calculate yaw, or wind direction in the plane, as you have said. Or yaw angle could be obtained from transducers in the swivel. Either way should work with a fixed or swiveled pitot tube.
 
  • #92
How can one possibly ascertain speed by way of measuring an external, dynamic medium?

Regardless of algorithims, this is inherently flawed. There is NO WAY that anyone can tell me that algorithims are sufficient to compensate for, example, a sudden 100mph wind shear to accurately tell me how fast my plane is flying. Indeed, I have NO IDEA that the wind shear is actually 100mph other than a reference to the plane.

One needs a static reference point, independent of the dynamic medium the plane is flying through.
 
  • #93
pallidin said:
How can one possibly ascertain speed by way of measuring an external, dynamic medium?...One needs a static reference point, independent of the dynamic medium the plane is flying through.
But the dynamic medium is what you are interested in. Flying depends on the relative velocity of the wind over the aerofoil, the velocity of the plane relative to the ground is pretty irrelevant except to tell you how late you will be.
 
  • #94
mgb_phys said:
But the dynamic medium is what you are interested in. Flying depends on the relative velocity of the wind over the aerofoil, the velocity of the plane relative to the ground is pretty irrelevant except to tell you how late you will be.

OK. That makes sense. Sorry for my rant.
 
  • #95
Weather is a simpler explanation than lightning

Lighting strikes of air-craft are common and foreseeable. Though it is
quite likely the system will be disturbed its computers should reboot
quickly and enough come up to provide quorum in time. Some one I know
who flies Airbus has had some boot up anxiety when his aircraft was
struck coming into land. The system came up again and after having no
control the approach was no longer suitable for an instrument landing,
but still good enough for a manual landing. As the system was up he
wanted to get the aircraft down while it was still responding so he
performed a manual landing. It was then in the shop for lots of time
consuming diagnostics.

Aircraft used in Australia frequently cross the tropics so they are
fitted with radar that can detect inter-tropical convergence. The Air
France crash telemetry reported garbage which could mean that it may
have flown into this. The last burst of data could be from a fatally
damaged aircraft after it as flown into something that it could not
withstand.
 
  • #97
It sounds like aircraft flying in such conditions could do with a redundant GPS to determine speed, which could serve to alert the pilot/system that the pitot tubes may be giving erroneous data.

Aircraft used in Australia frequently cross the tropics so they are
fitted with radar that can detect inter-tropical convergence.
Perhaps such equipment (Doppler radar?) should be mandatory on ALL commercial aircraft flying through the topics.
 
  • #98
Astronuc said:
It sounds like aircraft flying in such conditions could do with a redundant GPS to determine speed, which could serve to alert the pilot/system that the pitot tubes may be giving erroneous data.
But the GPS gives you absolute speed whereas what you need is 'relative to the airflow' speed
 
  • #99
Yes - I understant that. I was thinking in terms of changes of speed and position. In theory the system would monitor for changes in air speed (assuming pitots are working properly) with changes in actual speed, and consistency in those trends.


Perhaps pitot tubes need so laser doppler anemometry as backup, or at least someway to determine of they are plugged or otherwise not operating properly.
 
  • #100
I think they already do a lot of filtering to ignore sudden changes in pitot readings.
the danger is if they gradually ice up and start reading low you don't know you aren't going into a headwind.
But you would have thought with enough of the units you could detect a trend, if 1 probe shows you slowing more than the other two then something is wrong.

Even a simple backup flow meter would be useful. I wonder if you could use the load on the engine fan? They are basically just 8ft diameter windmills !
 
  • #101
mgb_phys said:
Even a simple backup flow meter would be useful. I wonder if you could use the load on the engine fan? They are basically just 8ft diameter windmills !
They're not windmilling though. They are being driven. Each engine does have it's own inlet condition sensors usually a total inlet pressure. In a pinch they could be used to give a good estimate of aircraft speed via inlet velocity. This would mean simply pulling data from the FADECs. I really don't know how feasible that really is though.
 
  • #102
Astronuc said:
Doppler radar

Not any dopper radar.

They have altitude, ground speed and rate climb which sees the ground. This does not help keep it stable in the air, but you want to know where the ground is.

A Pitot tube is required to get actual air speed.

The radar to detect most cases of inter-tropical convergence is very expensive and was not the standard weather radar with Airbus. Radar can't see air itself.

Shorter wavelength radar is required to detect smaller particles moving with the air. There is a lot computing required to present something that relates to hazards to the flight crew.

Presentation of hazards is very important as there is information overload.

Heating the air speed sensors may be a simple fix for icing. (These have been taped over for paint jobs and not untaped with disasterous results.) It is worrying that air-speed sensor issues were known issue before the crash.

The last telemetry could be any thing including catastrophic aircraft failure. (Fly the heavies the wrong way and they fall apart. You can't fly into weather that is not what the aircraft was designed to fly in.) The recorders if found would have much more info.
 
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  • #103
zagam said:
(... You can't fly into weather that is not what the aircraft was designed to fly in.) ...
And what would weather could that possibly be?
 
  • #104
There is lots of weather you can't fly into. It's all about control.

Inter-tropical convergence is bad because you or radar may not see it.
Enhanced Turbulence Radar (ETR) can see much more.

Even a small bum steer from the many sensors could have lead to loss of control of the aircraft "coffin corner".

Australia has a similar directive to FAA
AD/A330/108 Thales Pitot Probes 11/2009
http://casa.gov.au/wcmswr/_assets/main/airworth/airwd/ADfiles/OVER/A330/A330-108.pdf"

None for ADIRUs (Air Data Inertial Reference Unit) yet, but Perth to Singapore has been known to get exciting at certain point. Pure speculation that squark ident (radar reply) may be missed so aircraft is lit up by targeting radar (which uses primary echo only). Could this powerful RF beam mess up electronics?

http://www.google.com.au/search?q=perth-singapore+base+adiru"

Not quite as bad as being shot down like the Iranian one. Dropped comms frames suck.

The naval comms is very low frequency and this frequency could be close to symbol rate used for comms by all those sensors. Knowing that lightning will cause systems to reboot. Is the aircraft a big enough antenna to pick up enough VLF to mess up sensors?
 
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  • #105
http://www.breakingtravelnews.com/news/article/debris-from-af-447-located-in-atlantic-ocean/
 

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