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

[DaivdBender]

You have probally all heard about the Air France jet crashing in the Alantic.

Reports so far have suggested that lighting was the cause of failure.

Now I believe Commericial Air Crafts are struck by lightning at least once a year. Lightning is suppose to pass around the exterior of the plane causing only small distrubance.

From what I have read though lightning strikes can cause structural damage and electro-magnetic interference.

So the question is how safe are commercial jets against lighting strikes ?

How accurate are our models for predicting damage on a plane from lighting strikes ?

 

[russ_watters]

You have probally all heard about the Air France jet crashing in the Alantic.

Welcome to PF!

I was wondering when someone would post about this incident and I'm glad you did it in engineering instead of general discussion!

Reports so far have suggested that lighting was the cause of failure.

Now I believe Commericial Air Crafts are struck by lightning at least once a year. Lightning is suppose to pass around the exterior of the plane causing only small distrubance.

Correct, and since the initial reports, most news sources I've seen have backed off that speculation, noting that airplanes are designed to withstand lightning.

From what I have read though lightning strikes can cause structural damage and electro-magnetic interference.

So the question is how safe are commercial jets against lighting strikes ?

How accurate are our models for predicting damage on a plane from lighting strikes ?

The easy answer is that they are very safe, but nothing can be completely safe. More specific, I can't be because I don't have a lot of specific knowledge of the testing and modeling of this. We have plenty of members with more specific knowledge of this subject than me, though, who I'm sure will weigh in...

 

[DaivdBender]

Thanks for the response.

I just read that "The head of communication at Air France said the plane, an Airbus A330, had probably been struck by lightning" so I'm not too sure what the deal is.

If it had been struck by lightning I wonder how it damaged the plane?

If the report was false then I guess it could be almost anything. Have to wait until the black box is found.

 

[FredGarvin]

A lot of work and certification testing goes into an aircraft and its engines. A proper ground path between major components is a mandatory design feature. We just finished lightning strike testing on one of our engines.

That being said, there is no way to ever predict the worst case scenario when it comes to mother nature.

Personally, I don't buy the lightning strike theory. It may have had a contributing factor, but I doubt it was the main factor. Unfortunately, it looks like we may never know.

 

[Astronuc]

Here is some information on the research of lightning and aircraft interaction.

http://www.sae.org/aeromag/features/aircraftlightning/

http://oea.larc.nasa.gov/PAIS/Concept2Reality/lightning.html
I've seen a video of some of these experiments, but I can't find it on the internet.


Lightning might have been a factor. There is some speculation that aircraft with composite material might be more vulnerable to lightning strikes - but as of now, that's speculation.


Commercial aircraft have lightning wicks (basically lightning rods) or protusions with which to facilitate the conduction current in a more controlled process.

Lightning Strikes Airplane [Boeing 747] During Takeoff



As Fred mentioned, it will be difficult to find in the mid Atlantic. The craft seems to have gone missing somewhere near the mid-Atlantic Ridge.

. . .
"The research area overhangs an underwater mountain range as big as the Andes," Prazuck said. "The underwater landscape is very steep."

. . . .
With nothing more to go on than the last point where Flight 447 made contact — about 745 miles (1,200 kilometers) northeast of the Brazilian coastal city of Natal — search teams faced an immense area of open ocean, with depths as much as 15,000 feet (4,570 meters).

http://news.yahoo.com/s/ap/brazil_plane

 

[Borek]

So far they have not even approximately located the plane.

Anybody knows what is a range of underwater locator beacons?

Obviously the range will depend on the equipment used for detection so there can be no easy answer to that...

 

[Astronuc]

Update: Some possible aircraft debris found along path of AF447.

http://news.yahoo.com/s/ap/20090602/ap_on_re_la_am_ca/brazil_plane

Air Force spokesman Jorge Amaral says the seats were spotted by search planes early Tuesday morning but that authorities cannot immediately confirm they were from the plane.

Also spotted were small white pieces of debris, material that may be metallic and signs of oil and kerosene, which is used as jet fuel.

The debris was found about 390 miles (650 kilometers) northeast of the Brazilian archipelago of Fernando de Noronha.

 

[DaveC426913]

Thanks for the response.

I just read that "The head of communication at Air France said the plane, an Airbus A330, had probably been struck by lightning" so I'm not too sure what the deal is.

If it had been struck by lightning I wonder how it damaged the plane?

If the report was false then I guess it could be almost anything. Have to wait until the black box is found.

Did I not hear in the report that the plane sent out a warning complaint of electrical problems shortly prior to radio silence? Presumably the lightning fried some critical navigation or flight component(s).

 

[DaivdBender]

Here is some information on the research of lightning and aircraft interaction.

http://www.sae.org/aeromag/features/aircraftlightning/

http://oea.larc.nasa.gov/PAIS/Concept2Reality/lightning.html
I've seen a video of some of these experiments, but I can't find it on the internet.


Lightning might have been a factor. There is some speculation that aircraft with composite material might be more vulnerable to lightning strikes - but as of now, that's speculation.


Commercial aircraft have lightning wicks (basically lightning rods) or protusions with which to facilitate the conduction current in a more controlled process.

Lightning Strikes Airplane [Boeing 747] During Takeoff



As Fred mentioned, it will be difficult to find in the mid Atlantic. The craft seems to have gone missing somewhere near the mid-Atlantic Ridge.
http://news.yahoo.com/s/ap/brazil_plane

Thanks for the information. A very good read.

 

[russ_watters]

Did I not hear in the report that the plane sent out a warning complaint of electrical problems shortly prior to radio silence? Presumably the lightning fried some critical navigation or flight component(s).

It also reported a cabin pressure loss, so I was thinking about it from the other direction: that wind shear had caused a structural failure, leading to both the cabin pressure loss and electrical failures. But I haven't seen it reported what order the failures were reported in.

My gut reaction to the early news reports was to think about the last time this many people died in a plane crash: in 2001, when wake turbulence and possible pilot or computer overcorrection tore the tail off an A300 over New York. http://en.wikipedia.org/wiki/American_Airlines_Flight_587

We certainly can't rule out lightning completely, but it would be an exceedingly rare failure. Lightning hasn't taken down a commercial airliner in more thana 40 years and an average, every airliner is hit by lightning once a year, so there have been millions of lightning strikes since then.

 

[DaveC426913]

We certainly can't rule out lightning completely, but it would be an exceedingly rare failure. Lightning hasn't taken down a commercial airliner in more thana 40 years and an average, every airliner is hit by lightning once a year, so there have been millions of lightning strikes since then.

IIRC, often air accidents are a conflagration of events. Lightning in conjunction with some other element(s), such as the age of the plane may be the cause. I heard early reports mentioning how old the plane was, though I think they said it was only 4 years or something.

 

[Phrak]

I don't suggest this as the most plausible, or even likely cause, but not beyond some consideration. It's not unheard of that ball lightning can enter an aircraft.

http://www.straightdope.com/columns/read/2562/does-ball-lightning-really-exist"

Physicist R.C. Jennison claimed that he had personally witnessed ball lightning during an airplane flight. What's more, he'd reported the incident in a letter to Nature two years earlier. Here's the nub:

I was seated near the front of the passenger cabin of an all-metal airliner (Eastern Airlines Flight EA 539) on a late night flight from New York to Washington. The aircraft encountered an electrical storm during which it was enveloped in a sudden bright and loud electrical discharge (0005 h EST, March 19, 1963). Some seconds after this a glowing sphere a little more than 20 cm in diameter emerged from the pilot's cabin and passed down the aisle of the aircraft approximately 50 cm from me, maintaining the same height and course for the whole distance over which it could be observed.

 

[Phrak]

Here is a weather analysis in the vicinity of AF447.

http://www.weathergraphics.com/tim/af447/"

Wikipedia has the most comprehensive ACARS (Aircraft Communications Addressing and Reporting System) transission sequence I've seen so far. ACARS is the autonomous data broadcaste system the A330 utilized to report fault conditions directly prior to it's demise. It's about four screens down under "Incident".

 

[Borek]

Wikipedia has the most comprehensive ACARS (Aircraft Communications Addressing and Reporting System) transission sequence I've seen so far. ACARS is the autonomous data broadcaste system the A330 utilized to report fault conditions directly prior to it's demise. It's about four screens down under "Incident".

Can't find it - can you please give more detailed pointers?

 

[Borg]

And, there is already a Wikipedia page for this flight as well.

http://en.wikipedia.org/wiki/Air_France_Flight_447"

 

[LURCH]

Could have been positive lightning (BIG maybe).

 

[Vals509]

it was shown on the news that half an hour after last contact, weather satellites recorded extreme weather near where the plane was. could bad weather have crippled the plane.

also just as a guess. could the plane have suffered engine failure while in the storm. after all, there were electrical problems and i think the engines provide some power and also the engines i believe maintained presurisation and it is thought that there was a cabin loss of pressure

 

[Borek]

Pure speculation if you ask me.

 

[Mech_Engineer]

Whatever happened to the plane, it had to have been so chatastrophic that all communications and flight controls failed such that the pilots could not control the plane AND could not radio out a mayday. Possibly massive wind shear causing the airframe to break apart, but it seems to me that lightning is unlikely due to the number of double and triple redundant systems governing critical systems such as flight controls.

 

[mgb_phys]

also just as a guess. could the plane have suffered engine failure while in the storm. after all, there were electrical problems and i think the engines provide some power and also the engines i believe maintained presurisation and it is thought that there was a cabin loss of pressure

The engines normally provide all the electrical power, there is an emergency wind powered generator that deploys automatically if they fail. Losing both engines in cruise isn't a disaster - a 747 glided for 15minutes after losing all 4 engines when flying through a dust storm. Another A330 that ran out of fuel flew for 20 minutes before landing in the Azores.
The engines are used to pressurize the cabin and provide the heating and AC but the air doesn't suddenly rush out if they stop.

The sequence of events and debris look like it broke up at altitude but it's going to take the recovery of more evidence to work out why.

 

[Borg]

The engines normally provide all the electrical power, there is an emergency wind powered generator that deploys automatically if they fail. Losing both engines in cruise isn't a disaster - a 747 glided for 15minutes after losing all 4 engines when flying through a dust storm. Another A330 that ran out of fuel flew for 20 minutes before landing in the Azores.
The engines are used to pressurize the cabin and provide the heating and AC but the air doesn't suddenly rush out if they stop.

The sequence of events and debris look like it broke up at altitude but it's going to take the recovery of more evidence to work out why.

I agree. The plane that crashed into the Hudson in January lost both engines but that didn't stop them from performing a controlled crash landing and communicating with the control tower.

I've read reports that the automated messages from 447 were sent over a 4 minute time span. But, I've only read that the plane depressurized and had electrical failure - nothing about the order or timing. Has anyone heard anything more about the sequence, timing and content of the messages?

 

[Borek]

According to Polish media (they claim to quote some Brazilian media) pilot reported that they are going through thunderstorm. 10 minutes later plane systems reported that autopilot has been switched off, reserve power system has been engaged and systems required for plane stabilization have been damaged. Other reports followed. Three minutes later came report about pressure loss and electrical failures.

Note that this was first translated from Spanish to Polish, then from Polish to English, and neither translation was done by someone aware of proper terminology.

 

[Borg]

Note that this was first translated from Spanish to Polish, then from Polish to English, and neither translation was done by someone aware of proper terminology.

My wife is Russian. I definitely know how things get lost in translation...

 

[mgb_phys]

I've read reports that the automated messages from 447 were sent over a 4 minute time span. But, I've only read that the plane depressurized and had electrical failure - nothing about the order or timing

from http://aviation-safety.net/database/record.php?id=20090601-0

starting at 02:10 UTC, a series of ACARS messages were sent -automatically- from the plane. The first message indicated the disconnection of the autopilot followed and the airplane went into 'alternate law' flight control mode. This happens when multiple failures of redundant systems occur.
From 02:11 to 02:13, multiple faults regarding ADIRU (Air Data and Inertial Reference Unit) and ISIS (Integrated Standby Intsruments System) were reported. Then on 02:13 the system reported failures of PRIM 1, the primary flight control computers that receive inputs from the ADIRU and SEC 1 (secondary flight control computers). The last message at 02:14 was a 'Cabin vertical speed' advisory.

The ACARS is a SMS message like system that reports flight information and all sorts of diagnostic and system status messages. It let's the airline know of any technical problems that might need looking at when the plane lands. It's completely automatic and each short message only takes a fraction of a second to transmit so it could have managed to send messages as long as the systems had backup power and the antennae was connected - even if the plane was in pieces.

 

[Borg]

from http://aviation-safety.net/database/record.php?id=20090601-0

Thanks for the great link. This link from that page states that the final 'cabin vertical speed' message indicates that the plane was mostly intact at that time.
http://blogs.news.sky.com/foreignmatters/Post:0fc148fa-4542-4246-99e7-c0a8824562e6"

I found this page that describes what Alternate Law means:
http://www.airbusdriver.net/airbus_fltlaws.htm"

 

[Phrak]

Can't find it - can you please give more detailed pointers?

Sorry about that Borek. It's the same wikipedia article that borg has in post #34.

According to the article, which I've reformatted:

The last contact with the aircraft was at 02:14 UTC, four hours after take-off, when its avionics automatically transmitted several messages via ACARS indicating multiple systems failures.

1) The first of these messages, at 2:10 UTC, reportedly indicated that the autopilot had disengaged and the fly-by-wire computers had switched to an alternate program used in the event of multiple system failures.

2) Next, the aircraft transmitted several messages indicating failures of

A) the Air Data Inertial Reference Unit,

B) the Integrated Standby Instrument System (a backup system providing basic flight instruments), and

C) the master units of the primary and secondary flight control computers.

3) The final message received, at 02:14 UTC, indicated a possible cabin depressurization at location 3°34′40″N 30°22′28″W / 3.5777°N 30.3744°W / 3.5777; -30.3744.

 

[Phrak]

What elecrical failure?? The first fault transmitted by ACARS, according to the Wikipedia article, was multiple subsystems failures. This appears to have morphed into “electrical circuit malfunction.” For all we know the tail was ripped off along with it's remote sensors.

Edit: OK, nevermind the tail ripping off. These subsystems are probably located in the bays beneath the cockpit.

 

[FredGarvin]

It all fits pretty well into an extremely unlucky lightning strike scenario...except the cabin depressurization.

No one has mentioned the "B" word yet.

 

[mgb_phys]

It all fits pretty well into an extremely unlucky lightning strike scenario...except the cabin depressurization.

The message could mean the airframe had broken up .

No one has mentioned the "B" word yet.

Especially since it's about the only other cause of no-warning loss of an aircraft in cruise.

 

[russ_watters]

It all fits pretty well into an extremely unlucky lightning strike scenario...except the cabin depressurization.

What about the wind shear and breakup idea? Would the tail ripping off (like that one in 2001) cause such flight control failures? Are these flight control failures certain computer failures or could they be the computer's necessary reaction to a change in aircraft controllability or loss of sensors (whether electrical or physical)?

From what I understand, there are two debris fields, several miles apart. And 4 minutes to crash from 35,000 feet is pretty quick, about 100 mph. That's probably about the terminal velocity of a falling chunk of airplane. Could wind shear have torn off the tail or a wing (or two?)?

No one has mentioned the "B" word yet.

Due to the weather element, I don't know that it needs to be part of the discussion (yet). The media has shown unusual restraint.

 

[FredGarvin]

The storm causing a break up is a good idea considering what happened in the Rockaways to an A320. That happened due to rapid course corrections. I wonder what they think could happen with 100 mph shear winds hitting the tail section?

I don't know that aircraft's systems at all. I wonder what systems are routed through the tail end.

Ugh. What a way to go.

 

[russ_watters]

Especially since it's about the only other cause of no-warning loss of an aircraft in cruise.

Given that the lightning stike thing thing hasn't happened in 40+ years, any other resonable scenario must be considered. There are at least a couple of other reasons why a plane might suddenly plummet from a seemingly normal cruise:

-Fuel tank explosion, a la TWA 800
-Fire, a la ValuJet

 

[russ_watters]

The storm causing a break up is a good idea considering what happened in the Rockaways to an A320. That happened due to rapid course corrections.

...breaking off the vertical stabilizer.

I wonder what they think could happen with 100 mph shear winds hitting the tail section?

I'm also wondering if a microburst hitting a plane at cruising speed could cause enough of a vertical (negative) g-force to rip off the wings. That would have the effect of a sudden -20 degree angle of attack change.

I don't know that aircraft's systems at all. I wonder what systems are routed through the tail end.

Certainly sensors associated with rudder and elevator position at the very least. If the flight control computer doesn't see an input from one of them, could it revert to another operating mode?

 

[mheslep]

...No one has mentioned the "B" word yet.

I thought the fact that the flight avionics had the opportunity to radio home about several electrical problems made that somewhat unlikely.

 

[russ_watters]

I thought the fact that the flight avionics had the opportunity to radio home about several electrical problems made that somewhat unlikely.

Not really - the ones that have happened before haven't completely torn apart the plane, just damaged it enough to make it unflyable. Ie, Pan Am 103.

[edit] Just read up on TWA 800. That one was apparently, that catastrophic: the plane just abruptly disappeared, electronically. The flight data recorders were intact and simply stopped recording and the transponder stopped tranmitting.

For Pan Am 103, I was wrong, though: the wiki says that while the explosion only punched a 20 inch hole in the fuselage, but the secondary effects, structural damage and aerodynamic forces were enough to rapidly tear apart the plane... but not violent enough to kill the passengers. It's a little disturbing to think about, but in most such cases (and in the Shuttle Challenger!), the passengers were almost certainly killed by impact with the ground, not by the explosion/breakup of the aircraft.

[edit2] TWA 800 was particularly gruesome. Though the explosion was much bigger than Pan Am 103's, the damage was more localized and complete -and not huge, meaning the damage didn't affect the rest of the plane at all. Ironically, this led to a very similar crash scenario: the nose separated from the fuselage and fell intact and the body with the wings continued intact in a separate piece. Most of the passengers surely survived the explosion and those in the back 3/4 of the plane rode a burning but still flying piece of airplane until it pitched up enough to rip off the wings (probably only a few seconds), then fell, in flames. It must have been horrible.

 

[mgb_phys]

What about the wind shear and breakup idea? Would the tail ripping off (like that one in 2001) cause such flight control failures? Are these flight control failures certain computer failures or could they be the computer's necessary reaction to a change in aircraft controllability or loss of sensors (whether electrical or physical)?

Flight587 was an airbus A300. The pilot used full rudder in flight which you aren't supposed to do, the vertical stabilizer failed at about twice it's design load. After this Airbus fitted software to all it's fly by wire systems which stop the pilot breaking the aircraft. This is a little controversial as some traditionalist pilots claim it could stop them recovering in a very extreme situation.

From what I understand, there are two debris fields, several miles apart. And 4 minutes to crash from 35,000 feet is pretty quick, about 100 mph.

4 minutes is the time between error messages, ie between the autopilot disengaging and the assumed failure of the cabin. The time to impact is unkown

I thought the fact that the flight avionics had the opportunity to radio home about several electrical problems made that somewhat unlikely.

Not necessarily, if something ripped a hole in the body destroying major bits of the avionics+control system the system could have sent the error messages before the cabin lost pressure and the ACARS failed.

I'm also wondering if a microburst hitting a plane at cruising speed could cause enough of a vertical (negative) g-force to rip off the wings.

Microbursts don't rely stress the airframe like that. If a bunch of air the plane is sitting in suddenly accelrates downwards the airframe goes with it there is no net stress on the wings. Microbursts are only a danger when you are near the ground - where suddenly being thrown down 1000ft might be bad news if you are only 900ft up!

Wings can also take a lot of stress, 787 wing being loaded to 150% of it's maximum design load

 

[Phrak]

[edit] Just read up on TWA 800. That one was apparently, that catastrophic: the plane just abruptly disappeared, electronically. The flight data recorders were intact and simply stopped recording and the transponder stopped tranmitting.

[edit2] TWA 800 was particularly gruesome. Though the explosion was much bigger than Pan Am 103's, the damage was more localized and complete -and not huge, meaning the damage didn't affect the rest of the plane at all. Ironically, this led to a very similar crash scenario: the nose separated from the fuselage and fell intact and the body with the wings continued intact in a separate piece. Most of the passengers surely survived the explosion and those in the back 3/4 of the plane rode a burning but still flying piece of airplane until it pitched up enough to rip off the wings (probably only a few seconds), then fell, in flames. It must have been horrible.

I think the official report of TWA 800 is discountable.
The last I heard of it on public channels, it was aired on NBC with graphics supplied by the CIA involving the conclusion of a flame front chassing the plane then igniting the center tanks. The early official story evolved from plausible to ad hoc. It stinks of team spirit.

 

[Phrak]

Commerical oceanic airliners are required to have instruments in thriplets (two for over-land flights).

For instance, there are 3 ADIRUs (Air Data [and] Inertial Reference Units). There are three flight computers. If the first pair disagree, they are shut down, and the third assumes control.

The first indicated failures that, apparently, caused the autopilot program to relenquish control, were from the ADIRUs and the ISISs. These are located in instrument bays somewhere in the main airframe. Probably under the cockpit.

Concerning cabin pressure of the last transmission, in the goof lingo used in commercial aviation, I read "Cabin vertical speed" advisory to mean what you all have thought it to be: a drop in cabin pressure. Thanks for the link MGB...

But the initial failures reported occurred in the ADIRUs and the ISISs. These are equipped with redundant power sources: 120V/400Hz, 28V and 28V battery backup. They are equipped with lightning supression circuits. Can they protect against all overvoltage spikes producted by lightning? I don't see how.

 

[russ_watters]

Flight587 was an airbus A300. The pilot used full rudder in flight which you aren't supposed to do, the vertical stabilizer failed at about twice it's design load. After this Airbus fitted software to all it's fly by wire systems which stop the pilot breaking the aircraft.

I'm not suggesting the pilot caused it, what I'm suggesting is a scenario where even the flight control computer couldn't respond fast enough due to the extreme severety of the wind event. If a plane moving at 500mph hits an area where the wind is pointed downward at 150mph, geometry tells us that it now has an angle of attack of -17 degrees. An angle of attack of -17 degrees at such speeds would cause an enourmous aerodynamic stress.

4 minutes is the time between error messages, ie between the autopilot disengaging and the assumed failure of the cabin. The time to impact is unkown

Good point.

Microbursts don't rely stress the airframe like that. If a bunch of air the plane is sitting in suddenly accelrates downwards the airframe goes with it there is no net stress on the wings.

A rapid acceleration is a g-force. A microburst pushes the wings down quickly, and the wings pull the fuselage down. That's a lot of airframe stress.

Wings can also take a lot of stress, 787 wing being loaded to 150% of it's maximum design load

Define "a lot" and 150% of what?. Just about any plane other than a fighter is capable of destroying itself via aerodynamic forces. 3-4 g's (positive) is not a lot of strength compared to the potential magnitude of the aerodynamic forces.

 

[russ_watters]

I think the official report of TWA 800 is discountable.
The last I heard of it on public channels, it was aired on NBC with graphics supplied by the CIA involving the conclusion of a flame front chassing the plane then igniting the center tanks. The early official story evolved from plausible to ad hoc. It stinks of team spirit.

Conspiracy theory is not allowed here. The official report is the authority on the subject.

 

[Phrak]

Conspiracy theory is not allowed here. The official report is the authority on the subject.

Of course. People never, ever conspire. It is not out human nature. Not even when two are speaking in private. My bad.

 

[russ_watters]

Here's an interesting plane crash where a change of CG due to the pilot going to the bathroom (!), combined with wind shear caused the breakup of a small plane:

It appeared that the pilot's decision to go to the bathroom shifted the weight of the already unbalanced plane and caused it to become unstable and uncontrollable while in an area of strong turbulence. The nose of the plane slowly pitched up and then abruptly dropped just before the crash. In three seconds, the plane rose more than 100 feet with its nose down, and was then rocked by wind shear three times greater than what is defined as extreme turbulence. Within the first 12 seconds that they encountered problems, the G-force shifts rendered the crew and passengers incapacitated and unconscious and caused the breakup of the aircraft in flight.

http://aviation-safety.net/database/record.php?id=20010303-0
Relevant fresh news story:

Ten minutes later, a cascade of problems began: Automatic messages indicate the autopilot had disengaged, a key computer system switched to alternative power, and controls needed to keep the plane stable had been damaged. An alarm sounded indicating the deterioration of flight systems.

Three minutes after that, more automatic messages reported the failure of systems to monitor air speed, altitude and direction. Control of the main flight computer and wing spoilers failed as well.

The last automatic message, at 11:14 p.m., signaled loss of cabin pressure and complete electrical failure — catastrophic events in a plane that was likely already plunging toward the ocean.

"This clearly looks like the story of the airplane coming apart," the airline industry official told The Associated Press. "We just don't know why it did, but that is what the investigation will show."

Now that's a long time from first failure to the likely time of break-up, so my idea of a microburst basically just snapping the plane in half is unlikely. It doesn't mean it couldn't have caused damage that led to a later break up, though.

One fear — terrorism — was dismissed Wednesday by all three countries involved in the search and recovery effort. France's defense minister and the Pentagon said there were no signs that terrorism was involved, and Jobim said "that possibility hasn't even been considered."

So there that one is, Fred.

http://news.yahoo.com/s/ap/brazil_plane

 

[russ_watters]

Interesting article about this crash and a "brutal freak turbulence" theory:

Brutal freak turbulence is the most plausible cause of the crash of Air France Flight 447. If lightning alone caused the crash questions would be asked about the design of the A330, a medium-sized long-range airliner that enjoys a high reputation with the world's airlines...

The best-known case of turbulence causing a commercial airliner crash was when a BOAC flight from Tokyo to Hong Kong went down near Mount Fuji in 1966 after encountering a storm.

All 113 passengers and 11 crew on board were killed and the subsequent inquiry found the probable cause of the disaster was that “the aircraft suddenly encountered abnormally severe turbulence which imposed a gust load considerably in excess of the design limit.”

http://www.blnz.com/news/2009/06/01/Analysis_turbulence_lightning_most_likely_r_Fr.html

From the wiki on that crash:

A U.S. Navy A-4 Skyhawk that was sent up shortly after the accident to search for the wreckage encountered extreme turbulence in the accident area. The cockpit accelerometer display registered peak acceleration values of +9 and -4 g-units, causing temporary loss of control, and leading the Navy pilot to believe his aircraft would also break-up in the turbulence. The pilot regained control and landed safely, but the aircraft was grounded for post-flight inspection by maintenance personnel. Many other aircraft that passed near Mount Fuji that day also reported moderate to severe turbulence.

http://en.wikipedia.org/wiki/BOAC_Flight_911

So that example is of exactly the type of thing I was speculating about. But it also is 40 years old.

 

[Phrak]

Here's my scenario.

I presume Airbus builds it's nose cones from carbon fiber. Why? because of the compound curvature of the surface and Airbus's dedication to reducing fuel costs from any quarter. If they don't build it from carbon, nevermind, I'm up the wrong tree.

Carbon composite has far greater bulk resistivity than aluminum. Electical damage to semiconductors was once identificed as coming from both electrostatic discharge and induced electromagnetic induction (ESD-EMI). Lighning has a great capability for induction. Changing fields on one side of a carbon fiber barrier can transmit to the other side. Simply put, carbon fiber makes a poor Faraday cage. On the other side of the nose cone resides the main avionics systems, as far as I can tell.

I surmise that lightning penatrated the nose and took out the main avionics.

 

[Borek]

Anybody knows if navy submarines are used to help localize black box? They are equipped with the state of the art hydrophones, they can be at the site in a blink (well, much faster than surface vessels) and they are not limited by the weather.

Could be it is not as easy - their hydrophons can be optimized for other frequencies and for other directions, but the idea seems plausible to me.

 

[Borek]

They say pilot slowed down - perhaps too much - before flying into the thunderstorm area.

I wonder where this information came from.

 

[Mech_Engineer]

Anybody knows if navy submarines are used to help localize black box? They are equipped with the state of the art hydrophones, they can be at the site in a blink (well, much faster than surface vessels) and they are not limited by the weather.

Could be it is not as easy - their hydrophons can be optimized for other frequencies and for other directions, but the idea seems plausible to me.

I don't hydrophones will be very useful in finding a black box under water, unless it sending out a sonic signal. What they need is a very sensitive RF scanning setup (assuming the black box is transmitting an RF signal), and possibly side-scanning sonar (although that assumes there are large pieces of the plane sitting at the bottom of the ocean, rather than small debris fields).

 

[mgb_phys]

I'm not suggesting the pilot caused it,

I meant that it wasn't the wind that blew the stabilzer off, the pilot turned it full to the sie while flying along at several hundred mph.

what I'm suggesting is a scenario where even the flight control computer couldn't respond fast enough due to the extreme severety of the wind event.

It doesn't try, the software detects very rapid movements and let's them happen - it's better to be moved off course or off altitude briefly than waste fuel and stress the airframe by fighting every gust.

If a plane moving at 500mph hits an area where the wind is pointed downward at 150mph, geometry tells us that it now has an angle of attack of -17 degrees. An angle of attack of -17 degrees at such speeds would cause an enourmous aerodynamic stress.

It's possible to have damage caused by very localised win shear, where one wing is being pushed up and one being pushed down. Small planes have been flipped over by this in say wake turbulence. But generally the change in pressure happens on scales larger than the wing chord so the entire lifting surface is being pushed down - which is much lower stress.

The 150% wing test always struck me as a slightly silly figure. It's 150% of the intended operating maximum - of course if you really design the operating maximum to be the worst conditions it could encounter then there is no need for 150%. But if you consider the maximum to be the maximum for normal use then 150% is too small a margin for some of the situations it could get into.

 

[mgb_phys]

I don't hydrophones will be very useful in finding a black box under water, unless it sending out a sonic signal. What they need is a very sensitive RF scanning setup (assuming the black box is transmitting an RF signal), and possibly side-scanning sonar (although that assumes there are large pieces of the plane sitting at the bottom of the ocean, rather than small debris fields).

It sends out a sonar signal - the designers did consider that aircraft will fall into the sea, RF doesn't go through miles of seawater very well.
The problem is that the sea is 4km deep with a rocky bottom, at that depth sidescan will tell you nothing.

 

[mgb_phys]

I presume Airbus builds it's nose cones from carbon fiber. Why? because of the compound curvature of the surface and Airbus's dedication to reducing fuel costs from any quarter. If they don't build it from carbon, nevermind, I'm up the wrong tree.

Almost all nosecones are made from some sort of composite. They house the weather radar and putting your radar antennae inside a faraday cage has performance issues.

Changing fields on one side of a carbon fiber barrier can transmit to the other side. Simply put, carbon fiber makes a poor Faraday cage.

True but irrelevant, the individual avionics and the wiring is very well shielded.
The main issue with composite airframes and lightning is electrically bonding panels together, if there is a break in electrical continuity between a panel that is hit and an adjacent one you get arcing which leads to damage.

On the other side of the nose cone resides the main avionics systems, as far as I can tell.

The avionics racks are under and behind the cockpit as on most planes. This was the cause of a loss of a 737 a few years ago where a blocked coffee machine had been dripping coffee onto them for years unnoticed until they shorted out. The original 737 also had a problem with toilet cleaner leaking into them. They are better protected on later models.