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

[Astronuc]

They are also saying some pilots reported seeing something consistent with a plane exploding and dropping to earth.

Perhaps that could have been lightning. Out there, the flights are at 34000+ feet.

I've flown in puddle jumpers past lines of thunderhead and at the base, it looked like blasts of light. There was also lighting above us, to the side and below us.


I think there was a Spanish flight in the vicinity.


It also reminds of the flight in South or Central America where a Boeing 737 encountered severe turbulence. The storm apparently caused the plane to roll sharply, and the crew overcompensated and rolled the plane upside down, or well beyond design. The plane ultimately nose-dived into the ground.

 

[Phrak]

: backs very carefully away from Phrak, deletes all correspondence linking us :

Ha! It took some good amount of time for me to figure what you were talking about.

 

[mgb_phys]

Entering a localized 100 mph up or downdraft hitting the wings causes a very rapid acceleration, whether the pilot/computer reacts to it or not. Sure, the wings can withstand such a distributed load and rapid acceleration - but they are connected to an airplane. The wings cannot accelerate the airplane up/down that fast without ripping the wings off at the root.

Yes I think I was missing your point.
Severe turbulance can do serious damage to a plane, although large planes aren't accelerated as violently as the small skyhawk.
The china airlines flight where the crew stalled and rolled a 747 had most of the tail ripped off - it's easily possible that severe turbulence tore a control surface or part of a wing off. Generally turbulence isn't a problem because planes avoid it - if they couldn't because there was no way around the storm, or the storm was much more violent than they thought then it is a very likely cause.

I used to fly to S America frequently and it does get very 'interesting' over the equator even without storms

 

[Phrak]

I can't find the maxium G loading, nevermind + or - , for the A330-200. How do you search for it anywho?

 

[russ_watters]

Yes I think I was missing your point.

Bizarre, you keep ignoring the example I gave. Maybe the third time's the charm:

While flying into the wind, approaching Mount Fuji from the downwind side, the aircraft encountered severe clear-air turbulence associated with lee waves, causing a sudden structural failure that initiated the in-flight breakup sequence. At the time of the accident, winds at the summit of Mount Fuji were measured at 60 to 70 knots from the northwest. Lenticular clouds associated with lee waves were observed on weather satellite photos taken 30 minutes before the accident some 240 km (150 mi) to the south, but were not visible in the vicinity of the accident where the skies were clear.

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

This is exactly what I am suggesting may have happened to the Air France flight. The plane in the incident above was literally ripped apart by a vertical wind event.

although large planes aren't accelerated as violently as the small skyhawk.

True, but given the magnitude of the acceleration the Skyhawk felt, it would only need to be about half as much to break up an airliner. In any case, there is no need to argue that point or this issue of whether it can happen at all: it actually happened. We know it is possible for a vertical wind event to rip apart a large airliner because it has happened before.

 

[russ_watters]

I can't find the maxium G loading, nevermind + or - , for the A330-200. How do you search for it anywho?

According to this article, it is 2.5*150%=3.8g

http://www.aviationtoday.com/av/categories/atc/13015.html

 

[Phrak]

According to this article, it is 2.5*150%=3.8g

http://www.aviationtoday.com/av/categories/atc/13015.html

Well done! I don't know how I managed to pick the wrong keywords.

"For example, the pilot is not allowed to exceed the airplane’s 2.5-G design load, even though a 50% safety factor is built into the structure, suggesting that the airplane is strong enough to pull 3.8 Gs."

This hints that the airframe was distructively tested and failed at 3.8 Gs positive when spanking new, and Airbus decided to limit, via software, the pilot's ability to pull more than 2/3's of this, and perhaps quotes the 2.5G value as their specifications to purchasers.

From various insudry sources I've noted, the pilot shoud reduce airspeed by about 25 knots on the expectatation of turbulent atmospheric conditions. This is little compared to the cruise speed. The dynamic forces are recduced by 10%.

3.8 is a very nice number and should be encountered not far from stall angle of attack. This means that the wings won't ever encounter more than 3.8 Gs before stalling, or very little above it.

What this means is that they could still rupture on a 4 year old airframe with the right amount of shear.

 

[Borek]

That's not enough - they also need to find their way out of the plane.

I recall reading somewhere that there are planes where black box is mounted in such a way that it gets ejected by inertia on impact. Doesn't sound difficult to manage.

 

[Samj008]

I think it was mentioned earlier, but one pilot saw an intense white flash, extending vertically to the ground and lasting around 6 seconds, at the time the plane disappeared. Positive Lightning?

 

[Astronuc]

Interesting discussion here - http://en.wikipedia.org/wiki/Coffin_corner_(aviation ). The plane could have stalled, dropped precipitously, and perhaps achieved beyond design load conditions.

http://en.wikipedia.org/wiki/Lee_waves#Aviation


With cumulonimbus clouds, there can be significant up and down drafts.


Then there is this: Could a Computer Glitch Have Brought Down Air France 447?
http://news.yahoo.com/s/time/20090604/wl_time/08599190290700

Could the lightning have caused ADIRU failure or failure of multiple systems while the aircraft simultaneously encountered severe turbulence?

 

[herpamad]

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.

 

[DaveC426913]

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.

 

[Astronuc]

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.

. . . .

 

[mgb_phys]

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

 

[Borek]

French nuclear sub was directed to the area.

 

[Phrak]

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

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.)

 

[Phrak]

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.

 

[russ_watters]

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.

 

[Phrak]

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.

 

[russ_watters]

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.

 

[Phrak]

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.

 

[mgb_phys]

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!

 

[russ_watters]

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.

 

[jgrenwod99]

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.

 

[russ_watters]

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.

 

[jgrenwod99]

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.

 

[NateB]

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.

 

[russ_watters]

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...

 

[Astronuc]

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.

 

[Phrak]

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.