How safe are commercial jets against lightning strikes

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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.
 
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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.
 
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.
 
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.
 
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.
 
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.
 
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
 
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.
 
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 !
 
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.
 
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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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?
 
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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http://www.breakingtravelnews.com/news/article/debris-from-af-447-located-in-atlantic-ocean/
 
Hope they find the flight recorders; the data should be interesting to look over.

Edit: Here's an interesting http://pdf.aiaa.org/getfile.cfm?urlX=6%3A7I%276D%26X%5B%22G%2BR%40%5BNP4S%5EQ%2A%2B%225ZT%26%5EP%20%20%0A&urla=%25%2B2L%25%22PH%20%0A&urlb=%21%2A%20%20%20%0A&urlc=%21%2A0%20%20%0A&urld=%28%2A%22%40%20%23P%3EDT%21%2C%20%0A&urle=%27%28%22X%21%23%40NFU%40%20%20%0A on turbulence and creating a real-time system to predict turbulence.
 
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Wow, after all this time.

Will be interesting what they discover.
 
jarednjames said:
Wow, after all this time.

I just realized that it's been nearly two years since the crash occurred.

I don't recall how long the FDR and CVR transponders last, but given the amount of time that's passed I'm not optimistic they'll be found. We can still hope, though.
 
jhae2.718 said:
I don't recall how long the FDR and CVR transponders last, but given the amount of time that's passed I'm not optimistic they'll be found. We can still hope, though.
On the order of a few months. The only hope of finding them is to locate the part of the plane they were in when the plane crashed...with them still inside. But that may happen, since it would seem they found the main body of the airplane.

Also, a comment was made in an article I read that the oxygen masks were not deployed, indicating the plane did not break-up/depressurize prior to impact. Does anyone know if that is necessarily true? It would seem to me that they would require their own individual pressure sensors, power supply and oxygen source for that to be necessarily true. Otherwise, a rapid break-up of the plane could prevent them from deploying.
 
If I recall correctly, the flight control systems on Airbuses will override pilot inputs in certain cases. With the preface that this is speculative (if this isn't appropriate in this forum, let me know and I'll delete it.), one of the possible causes I heard was that the flight controls couldn't handle the failure of the pitot tubes, and ended up causing the a/c to crash while trying to correct. (Let's hope we get some real data to find out what actually happened.)

I don't remember hearing anything about a depressurization prior to impact. I believe that the oxygen masks deploy automatically.
 
russ_watters said:
Also, a comment was made in an article I read that the oxygen masks were not deployed, indicating the plane did not break-up/depressurize prior to impact. Does anyone know if that is necessarily true? It would seem to me that they would require their own individual pressure sensors, power supply and oxygen source for that to be necessarily true. Otherwise, a rapid break-up of the plane could prevent them from deploying.

I don't know for sure, but I think they are activated more by acceleration than pressure. Of course a sudden change of pressure would cause an impulsive force on them. I have heard of cases where masks were deployed with the aircraft on the ground in situations like landing gear collapsing, which clearly isn't going to cause a cabin pressure change.

They have their own (bottled) oxygen supply. For "normal" use the masks only need to provide O2 for long enough for the plane to descend to say 10,000 ft, which only takes a few minutes in an emergency situation where the plane is still controllable. Flying for 3 hours over water to the nearest airfield at 10,000ft in an unpressurised cabin isn't going to be fun for anybody, but it's unlikely to kill people, and there should be medical supplies available and cabin crew trained to administer them to the relatively few passengers who need them.

Those comments would suggest that the masks would deploy on impact anyway, if the plane was out of control. I don't know if the flight recorders have a channel for cabin pressure. If they do, that would give a definitive answer.

EDIT/UPDATE:

The above is not quite right. There are two things going on here. The system to drop the masks is pressure activated, but it can be incorrectly activated by impact etc.

However the masks do not start to deliver O2 until they have been "activated" by the user pulling them down to face level.

So in principle it is possible to tell from the wreckage whether the masks were actually used by the passengers, or if they just got shaken loose.
 
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jarednjames said:
Wow, after all this time.

Yup, the aviation industry takes safety seriously, even if it doesn't always get it right.

Reminds me of the time when I spent 6 months trying to figure out where something that fell off a plane 30,000 ft above the Amazon rainforest would have landed. We didn't succeed in funding that one, but if it ever turns up in a tree somewhere we will still be interested in it, even though we lost it 15 or 20 years ago.
 
Here's AvWeek's story: http://www.aviationweek.com/aw/generic/story.jsp?id=news/awx/2011/04/04/awx_04_04_2011_p0-305669.xml&headline=AF447%20Wreckage%20Found&channel=comm
 
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AlephZero said:
Reminds me of the time when I spent 6 months trying to figure out where something that fell off a plane 30,000 ft above the Amazon rainforest would have landed. We didn't succeed in funding that one, but if it ever turns up in a tree somewhere we will still be interested in it, even though we lost it 15 or 20 years ago.

Curioseur, curioseur.

You were working for Bond at the time?
 
Borek said:
Curioseur, curioseur.

You were working for Bond at the time?

Nope. It's usually easier to work out why something fell off when it wasn't supposed to, if you can actually look at what broke.

I didn't actually spend 6 months IN the Amazon rainforest (though there were people out there talking to the indigenous population). Most of my time was spent messing about with a wind tunnel, trying to estimate how far thing might have glided. And trying to find a meteorologist who would give a better estimate of the wind speeds at the time than "I don't know."
 
Things are looking up then.

Hopefully they'll get them out of the pond and they still work.
 
Good news!

It will be interesting to see what happened to AF447.
 
The cockpit voice recorder has been recovered as well. This apparently "completes" the search effort, now they have to see if they can extract the data and piece the events back together...

http://www.bbc.co.uk/news/world-europe-13264573
_52457957_011891456-1.jpg
 

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