AA77 FDR Data, Explained

[George 152]

I concur. This is starting to get rather plausible, in my opinion:

• The aircraft is at extreme speed and low altitude, stressing the aircraft
• The terrorists have the throttles firewalled, hitting max EGT and losing power
• They further entered a mild PIO, around a moderate pull-up of roughly 1.5 to 2 g's
• They may have struck ground obstacles or birds further out than is known
• The combined aerodynamic and other stresses shake the exterior, either enough to fail door sensors or actually pop doors open
• The engines may also experience mild compressor stall at this time
• All of this combines to create a glitch on the power bus, either by upsetting the engines, popping cables, or arcing somewhere in the aircraft
• Power failure on the main bus is also indicated by failure of avionics such as TCAS, as reported on the last valid FDR frame
• As the FDR data appears to be fully valid and uncorrupted, we accept this final report as plausible evidence of power failures on the aircraft
• The suspected power failure kills repeaters or the DFDAU, either leaving them unpowered or forced into a recycle
• Data stops arriving at the FDR, approximately six seconds before impact
• The FDR writes two empty frame markers after the last packet is transcribed, and then goes silent

Anything else? Again, there are of course other possibilities, but the above seems pretty darn reasonable to me.

This is how you know this is science, and not pseudo-science. We may never prove the answer, but the more we work on it, the more we know.

Looks pretty much as I'd reckon it happened.
A dollar that our quarrelsome one will ignore it ?

 

[wstutt]

Well, I thought I would take another crack at obtaining the compression algorithm. I spent some time with L3 Communications tech support to see if I could glean a little insight into the compression algorithm. He did tell me that they did not make a Model F-2100, but did make a FA-2100.

Unfortunately, he really did not give me much insight beyond what I already know and was tight-lipped about the algorithm. He did however say that he could sell me a copy of the ROSE software which would uncompress the file for me. I just did not have $7,000 to spare today for a licensed copy

Thanks for trying John.

Another possibility would be to give them a copy of the compressed file and get them to decompress it for us in to the ARINC 575/717 format mentioned in the NTSB report.

Warren.

 

[wstutt]

I asked Rob Balsamo the following question posed by beachnut:

The impact time from the report on the FDR is based on what?

His answer to that was:

That question is already answered by the NTSB. Tell beachy to read the pdf's.

I believe he is referring to Section II of the "Recorded Radar Data Study--all four aircraft.pdf" document and the information above it.

I asked him about the Time Correlation Report on this Pft thread that covers the topic of the recent posts here on this thread.
ETA: I didn't choose the name of that thread. Rob gave it that name when he split it.

Warren.

 

[jaydeehess]

Typical non-reply from Cappy Robby.

I see TF attributes bird strike hypothesis to me. Odd, it must be because its a long thread and he is reading every 3rd post.

Even more odd is that there is no mention of the loss of TCAS or the door open warnings in the thread Warren links to.

eta: I see Robby says the thread was split

 

[BCR]

Thanks for trying John.

Another possibility would be to give them a copy of the compressed file and get them to decompress it for us in to the ARINC 575/717 format mentioned in the NTSB report.

Warren.

They charge for that too

 

[apathoid]

Typical non-reply from Cappy Robby.

I see TF attributes bird strike hypothesis to me. Odd, it must be because its a long thread and he is reading every 3rd post.

Even more odd is that there is no mention of the loss of TCAS or the door open warnings in the thread Warren links to.

eta: I see Robby says the thread was split

Could they be any more pathetic? They have a couple of geniuses there as well.....I guess we'll have to start using smaller words.

"Should we also tell them the electronics take that A/C voltage and rectify it using well filtered electronics and convert to DC?"

Great insight Skippy. I had absoluetely no idea that AC could be converted to DC. Next you're gonna tell me that DC can be converted to AC...sheesh. I suspect beachnut, Mackey, jaydee and Warren had no idea either. Oh, and was there a point to that statement? The FDAU is powered by AC unless on standby power...

"Yes there is some mild voltage variation, and different (a whopping approx 1.08 VAC difference BTW) mean bus voltages between the 2 engines, but HINT: S.D.= [0.27544 VAC, 0.35797 VAC for the pair for the final time interval that I sampled]"

And which phase(s) are being sampled? You mean, there might be some voltage values that aren't recorded? What about frequency? What about phase to phase values? What about load percentage? Why bother troubleshooting electrical problems, when all I have to do is just interrogate the FDR. Oh and you'll never see less than 112 or more than 117-118, otherwise the GCU would trip the bus.

"Sorry to say (Mackey), but the design of the FDR does not allow for more than 500 milliseconds to pass before the next write event. Even if they want to cry about buffer content, they're up to one second of "missing data".

I don't think this genius realizes what we are actually hypothesizing. And all of them are still saying the FDR data doesn't support our assertions and that no data was lost. How can it record anything, if suddenly powered down. The AA587 and AA1400 examples just sailed right over their heads. grr

 

[wstutt]

Thanks for trying John.

Another possibility would be to give them a copy of the compressed file and get them to decompress it for us in to the ARINC 575/717 format mentioned in the NTSB report.

Warren.

I just wanted to add that there would appear to be some way of obtaining a decompressed file, since Snowygrouch mentioned having one in post #351 of this thread:

<snip>

...I have obtained ALL the data nessesary to complely dismember the origional .fdr file which I have in both compressed and uncompressed format.

<snip>

Also Undertow discusses one on this Pft thread.

Warren.

ETA: I hadn't seen John's reply that the file can be decoded for a fee when I posted this.

 

[R.Mackey]

I don't think this genius realizes what we are actually hypothesizing. And all of them are still saying the FDR data doesn't support our assertions and that no data was lost. How can it record anything, if suddenly powered down. The AA587 and AA1400 examples just sailed right over their heads. grr

Doesn't sound like they get it at all. Or perhaps they're just trying to muddy the waters, as usual...

One interesting thing to check would be just how the FDR is configured for power. It sounds like it runs off the mains, and can be switched to emergency power, but this takes time. Which makes sense if you think about it -- if the mains go down, you're not going to have most of your sensors powered anyway, and maybe not the instrumentation bus either, so what would be the point? You can't run the whole plane on the emergency bus, that's why there is such a thing.

The CVR, on the other hand, I'm beginning to suspect always runs off emergency power. It only records off a microphone, and that is fed to it on a dedicated line, not over the instrumentation bus. One could run this off the emergency power bus without much difficulty.

I bring this up because in several other cases, the FDR drops out while the CVR keeps on trucking, which is how we can figure out just where the FDR dropped out in the first place. I had been ascribing this to digital vs. analogue operation, and perhaps better brown-out performance in the CVR, but maybe there's a simpler explanation. Maybe the CVR never has to switch power sources, but the FDR does, when things start going haywire. And if this is true, then it makes our hypothesis above (the real one) even more plausible.

Anybody got a 757 handbook?

 

[BCR]

I just wanted to add that there would appear to be some way of obtaining a decompressed file, since Snowygrouch mentioned having one in post #351 of this thread:


Also Undertow discusses one on this Pft thread.

Warren.

ETA: I hadn't seen John's reply that the file can be decoded for a fee when I posted this.

If they have a decompressed version, then they should share the wealth. I have one of the best FDR specialists in the world (Warren, you know who he is now, but please keep him confidential for the time being) waiting to get his hands on it. A lot can be determined by the actual voltage transitions (waveform) which can be reconstructed with the uncompressed data. So if Snowy has it, why is he keeping it so secret?

 

[apathoid]

Doesn't sound like they get it at all. Or perhaps they're just trying to muddy the waters, as usual...

One interesting thing to check would be just how the FDR is configured for power. It sounds like it runs off the mains, and can be switched to emergency power, but this takes time. Which makes sense if you think about it -- if the mains go down, you're not going to have most of your sensors powered anyway, and maybe not the instrumentation bus either, so what would be the point? You can't run the whole plane on the emergency bus, that's why there is such a thing.

The CVR, on the other hand, I'm beginning to suspect always runs off emergency power. It only records off a microphone, and that is fed to it on a dedicated line, not over the instrumentation bus. One could run this off the emergency power bus without much difficulty.

I bring this up because in several other cases, the FDR drops out while the CVR keeps on trucking, which is how we can figure out just where the FDR dropped out in the first place. I had been ascribing this to digital vs. analogue operation, and perhaps better brown-out performance in the CVR, but maybe there's a simpler explanation. Maybe the CVR never has to switch power sources, but the FDR does, when things start going haywire. And if this is true, then it makes our hypothesis above (the real one) even more plausible.

Anybody got a 757 handbook?

It could also be a Left/Right Issue, The Left AC bus powering FDR system components, while the Right AC bus powers the CVR. I'll have something definite tomorrow.

 

[jaydeehess]

Yeah, AC converted to DC, what a concept. The fact that other than AC motors all electronics run on DC would explain why the very first cct that one gets to work on in college electronics courses are half wave AC rectifiers. You get to add components, first a capacitor then another diode, then two more diodes, it was fun.

 

[apathoid]

It could also be a Left/Right Issue, The Left AC bus powering FDR system components, while the Right AC bus powers the CVR. I'll have something definite tomorrow.

That is indeed the case.The CVR gets its power from the Right 115VAC Utility Bus, and the FDR/FDAU get their power from the Left 115 VAC Main Bus. I'm also looking at the schematic its apparent that FDAU and CVR only operate off AC, while the FDR has an additional 28VDC input right off the L 28VDC Bus, so it's always there. The AC is supplied by either having the FDR mode switch ON(NORM is the usual position), or when the plane is in the air through the #2 Air/Ground Relay, or on the ground with either engine running through the FDR Control Relays. I'll upload the schematics later.

eta: Also worth noting that the neither the FDAU nor the CVR can work off of standby power. That shouldn't really be a surprise, considering the only time the aircraft is running off standby power is when all power sources are dead, I'd rather have an ADI for 5 more minutes than an CVR recording of my final words. I'll have to look more closely at the DC Bus that the FDR is on to see whether or not it will run off the Battery Bus when in standby power mode, but I'm pretty sure it doesn't.

 

[beachnut]

Are the GEN control panel on the overhead?

 

[apathoid]

Are the GEN control panel on the overhead?

Yes. This is the overhead panel on a 767; pay no attention the chemtrail switch.

 

[Grimstad]

Not blown, stalled. Holy cow are those high EGTs.

You'd lose N1 just because of crap efficiency. High EGT means either a fire or (more likely) high inlet temperature, which means less air mass through the core and therefore less thrust and less cooling. Couple that with the high speeds and you are begging for compressor stall.

At those temperatures the engine's control laws would probably try to compensate by running rich, blowing excess fuel to cool off the core, and that could also create a smoke trail. Of course, I don't know exactly how that particular aircraft behaves, so it might not -- you can also cool EGT by leaning out the mixture, but that's a bit more dangerous.

But is this enough to cause havoc on the power bus? Could be...

The fan speed rollback coupled with increased EGT is interesting, especially considering the throttle position remained constant. On a typical GE or PW, there are only a couple of throttle settings where the relationships are inverse(bleed shift/flight to ground idle). Not normal at all otherwise IMO. You're spot on about the control settings. I believe that these motors are fly-by-wire and computer controlled. Even though you may exceed normal operational parameters, the Electronic Engine Control will sequence variable stators and and schedule fuel and air accordingly.

I got to watch this Boeing 777 ( mynorthwest.com/?nid=11&sid=162193 ) return to Sea Tac airport. I saw it at roughly 15:20 (an hour after take off) and had a perfect view of it. Right across my windshield 2.5 miles out at roughly my altitude (it was flying low over Puget Sound. It looked like 4000 – 5000 ft.). I posted a brief account in the comments section of that site.

It had a thick white cloud coming out of the left engine. It almost couldn’t be seen in front of the clouds but as soon as it got past it was a clear as day. I wish I had thought of taking a picture. I just thought I’d share. Since it was probably less than 10 miles from touch down and an hour after take off, I would assume the majority of fuel had been dumped.

 

[JoeyDonuts]

Yes. This is the overhead panel on a 767; pay no attention the chemtrail switch.

[qimg]http://www.internationalskeptics.com/forums/imagehosting/9902470641c092a41.jpg[/qimg]

It's got a "population control" switch! I knew it! Alex Jones was right! AAAAAAAAAaaaaaaa.....

*runs out into the street flailing arms wildly, then buys gold, bullets, and MRE's for a year*

 

[beachnut]

Yes. This is the overhead panel on a 767; pay no attention the chemtrail switch.

Hani just put in a big down stick, any terrorist in the cockpit could hit the overhead panel. Think the gen switches are guarded. If you hit some of those controls hard you could mess up the setting; turning off buss ties isolating a bus, etc. Not sure how they all work, but some of the controls look easy to use. Need some sim time to bump the buttons and see what happens.

The FDR data and on the animation the column had the biggest down stick when the data stopped.

In a KC-135 our generators could trip off in light or negative G, but after seeing flight 93 vertical acceleration extremes I think the Generators are not very sensitive to low G or negative G.

 

[apathoid]

I got to watch this Boeing 777 ( mynorthwest.com/?nid=11&sid=162193 ) return to Sea Tac airport. I saw it at roughly 15:20 (an hour after take off) and had a perfect view of it. Right across my windshield 2.5 miles out at roughly my altitude (it was flying low over Puget Sound. It looked like 4000 – 5000 ft.). I posted a brief account in the comments section of that site.

It had a thick white cloud coming out of the left engine. It almost couldn’t be seen in front of the clouds but as soon as it got past it was a clear as day. I wish I had thought of taking a picture. I just thought I’d share. Since it was probably less than 10 miles from touch down and an hour after take off, I would assume the majority of fuel had been dumped.

First of all to the JREF forum!

Looks like a Rolls Royce powered model there. They've been having lotsa trouble lately. If it was any other type besides a 777, I'd suspect a bird injestion. But I'm told, and I've seen a supporting video, 777 engines are frozen chicken proof!

Hani just put in a big down stick, any terrorist in the cockpit could hit the overhead panel. Think the gen switches are guarded. If you hit some of those controls hard you could mess up the setting; turning off buss ties isolating a bus, etc. Not sure how they all work, but some of the controls look easy to use. Need some sim time to bump the buttons and see what happens.

I suppose that's possible, and its the Generator Drive Disconnect Switches that are guarded, the control and isolation switches are not(the drives have to be reset on the ground by maintenance after being disconnected). They are rarely used.

 

[R.Mackey]

That is indeed the case.The CVR gets its power from the Right 115VAC Utility Bus, and the FDR/FDAU get their power from the Left 115 VAC Main Bus. I'm also looking at the schematic its apparent that FDAU and CVR only operate off AC, while the FDR has an additional 28VDC input right off the L 28VDC Bus, so it's always there. [...]

eta: Also worth noting that the neither the FDAU nor the CVR can work off of standby power.

Well, then I'd say that tears it. We have a valid mechanism for FDR drop-out common to several flights, including AA 77.

Both FDR and CVR also have some energy storage internal to their own boxes, but in the case of FDR, it can only power itself. It can't drive external sensors, probably can't drive A/D either. The CVR might, though, running the cockpit microphone on phantom power. Need an expert on CVRs to confirm this. But I think we've got an excellent candidate.

After all, the question isn't if AA 77's FDR is missing six seconds -- the radar data leaves no doubt. It's why. The fact that the very last data the FDR receives include glitches all over the place, some from structure (doors) and some from other avionics (TCAS and EICAS) is quite a coincidence.

Not proof, of course, just a theory, one that happens to make sense. And for darn sure it's better than the only alternative yet proposed...

 

[BCR]

Darn you guys are good

I've gone back to work on the FDR (Warren has inspired me) decode. Right now I'm converting his Hamming code over to VB. A little tough because the bitwise operators are not exactly as functional in VB as C# (I found a work-around though). I'm not sure I'll find anything that will add to what Warren has already found, but curiosity is getting the better of me. I'm thinking that even without the Huffman compression algorithm we should be able to learn something from the file structure related to the power issue.