Mr. Snuggles offered:
I know what a jackscrew is, and I'm wondering about this aircraft's jackscrew. After all, many have said in this space that this rapid climb is not something a pro pilot would do on purpose.

Quote... The NTSB also repeated recommendations for a crash-protected image recording system that would record the cockpit environment during the last two hours of a flight.


They will not have to call it a 'Cockpit Video Recorder'.....

CVR Details
 

The speakers are in the forward console, one each for the Capt and F/O.

There are no "panel mounted mics" that activate when the speaker switch is selected. There is a single "area mic" mounted in the CVR panel itself that is continuously active and recorded on a separate track on the CVR.

'boofhead' I believe you..
 

Back on 12 Jan 14:54 boofhead said the old radars were ok. I second the motion. My background is 25 years of military flying, back in the 60ties and 70ties. Even though I always had the luxury of a good navigator, between the two of them it got me through quite a few squall lines. No I did not penetrate any cells, I was vectored around them.[with that old radar].

The reason for my post is actually to express my surprise, how readily commercial pilots request max altitude for their aircraft, not knowing if it will put them 'on top'. Having flown the B-47 I am well aware of the coffin corner and how sloppy the controls feel up there. I would not penetrate any wx up there. Maybe more commercial pilots should find out how their ac will feel manually at max altitude. We also queried opposite traffic as to wx en route. Later when I flew the C-130 and encountered turbulence, I would kick off the autopilot and fly it manually. This way I could tell what forces were exerted on my aircraft. But then, I guess, I am ancient...

Someone said that would be nice to overlay the weather over the trajectory plot before crash.
See in link below an approximate, the time is 23:00 UTC and the flight path is the small yellow curve
http://www.mediafire.com/view/xxaocp...5e/weather.jpg

phoeniks...

you are not ancient...you are good.


about 25 years ago I started seeing people fly at max altitude close to T storms...I knew we were close on the margins you are talking about.

when I became captain I always flew lower (other things considered too)> In fact I routinely flew 4000' lower than the canned flight plans...fuel burn came out the same and I had a bit better margin for the unexpected turbulence.

I asked my friends about their take on G load margins and they were all flying at the max...why I asked ...they didn't even know what the G margins meant.

I respect you and your candor...I just hope the new guys start to think and get some perspective from our posts!

Phoeniks...B-47 eh? Respect. :ok:

Glendale...add me to the list of non-believers in the max altitude cruise near CBs or the upper shear zone of a jetstream. Or most places, really.

You can add me to the list of non-believers too. As I recall, the max certificated altitude of a VC10 was 43,000ft. When I was a young pilot, the training captain I was flying with, took us up to a little over 46,000ft on a training flight at a reasonably light weight in smooth air and with a good horizon, to demonstrate the high and low speed buffets. There was a margin of only a few knots between the two and one had to be very delicate on the controls when edging towards each limit.
It was a non-standard exercise but taught me never to go there in rough weather. Limitations are there for a reason. Adding a margin in bad conditions is good airmanship.

Are these statements still true for modern, digital CVR? For the analogue recording I believe that you can filter a lot, because "it is all there" but buried, in a digital recording there is nothing between the bits. It is a bit like all the higher frequency events not recorded on the FDR with 1 second sampling rate. An oscillation at 1.1 Hz is recorded as an oscillation at .1 Hz as the real frequency is masked by the sampling rate.
What is the sampling rate for digital CVR? How does it match with computer generated sounds (alarms, chimes, cavallery fanfare...) which are also having their own sampling rate or rectangular waveforms. I never worked with digital audio, do you also have some frequency changes similar to my FRD example, so a sound of 42 kHz sampled at 41 kHz is recorded as a 1 kHz sound?

Humans Can't hear ultrasound
 

I think you'll find that even young human ears can't hear anything above 20 kHz. CDs are sampled at 44.1 kHz, over twice the highest perceptible frequency to humans. This ensures lossless recording. This is shown by the Nyqvist-Shannon sampling theorem.

I'd imagine CVRs would use the same principle.

Volume
The Nyquist theorem says that with a sampling rate of F Hz you can faithfully reproduce signals with a frequency up to F/2 Hz. So for example a CD is sampled at 44 kHz and it reproduces sounds up to 22 KHz. This is hi-fi sound quality.

I found a Honeywell CVR/FDR manual which states that the CVR inputs are sampled at 8 or 16 KHz and thus can record sounds up to 3.5 or 6 kHz. (This gives some margin to the "Nyquist limit"). This is "telephone line" sound quality. I was slightly surprised that the sampling rate is so low. Probably a legacy from times when solid state memory was much more expensive.

Edit: I might add that in order to avoid sampling errors like you describe (aliasing), almost all digital systems use techniques such as a low-pass anti-aliasing filter before the digital sampler, or use oversampling i.e. a sampling rate several times the signal frequency.

You don't need to be a pilot to read the regs ;):

FAR 121.359 (g):

14 CFR 121.359 - Cockpit voice recorders. | LII / Legal Information Institute

Maybe your boom mike doesn't have a headset attached. :)

These are the U.S. requirements, they often filter down to other countries over time.

Yep, I think I commented earlier on this thread that many FO's try to look like they are doing everything but flying the plane while they are in the seat. I guess it's a generational thing. :(

Snow
 

This is "telephone line" sound quality


these are usually sampled at 8 k/c/s :}

You get excellent quality sound at 8 kHz sampling (300 Hz to 3kHz, not 3.5 kHz). 8 kHz 8 bit uLaw or aLaw is the standard for landline telephones and as very reader knows that's more than acceptable (NB mobile calls are far lower quality). Going to 16 kHz gives a higher upper frequency ( 7 kHz ) but in general that's only useful for engineering analysis rather than voice clarity.

Where there is a big difference is the number of bits in the sample. This affects dynamic range and so say with 16 bits you can hear clearly the slightest whisper as well as the loudest bangs. 16 bit 44.1 kHz sampling is also well beyond the usual human dynamic range which is why it's used in CD recordings (fake golden-ear pedants not withstanding).

All of these figures are pretty irrelevant these days. 8 bit 8kHz sampling is 64 kilobits per second. CD quality is 705 kbps - a factor of about 10. This is compared to the storage increases over the past few years of factors of thousands to millions.

May help
 

@FlightDream111 thanks for that link - also useful is the FAA upset recovery link at FAA TV: Airplane Upset Recovery, Part 2

HarryMann


At the time I read your post re equal opportunity I did think to myself that I may be entering a bear trap considering your usually erudite posts. I suppose the image I had in my mind of 8501 being in a tight high speed spiral at FL240 with perhaps a disoriented crew attempting to make sense of it all and the debris pics to date.

Unless this position means the actuator is fully extended (no idea which way it is installed) and the piston rod is bent and hence the rudder fixed in that position, I do not think that the current position of the rudder tells us anything else than the direction of gravity.

THS
 

I see they recovered the tail section, no doubt the THS screw or assembly should give some indication last position.


Something like this:


http://i337.photobucket.com/albums/n...aftBHtail1.jpg

Nice overlay but that's a false-colour infra-red satellite picture rather than a radar plot. The satellite picture will tell you the temperature of the cloud tops, which corresponds roughly to their altitude but it won’t show areas of precipitation or strong air movement.

The area where the Air Asia went down, purely looking at that picture, could be an active cell going from 1,000’ up towards the tropopause or it could be the remains of an old CB anvil/blow-off at 45,000' with nothing underneath. Given the gyrations of the aircraft, it’s probably going to turn out to be the former but you couldn’t say from that picture.

Yes, the audio bandpass doesn't greatly affect the ability to forensically extract speech from a cluttered audio environment. The technician visually edits audio spectrograms using software designed to identify and remove unwanted noises. It is vastly beyond tweaking an equalizer.

It is very sophisticated -- usually a cell phone ringing during speech can be removed so perfectly there is no significant artifact remaining.

The software already exists so it's not like they have to engineer something from scratch. In both music/video production and advanced audio forensics for law enforcement, audio technicians are highly trained using this software and accomplish amazing results.

Satellite images can give reasonable estimates of precipitation. This one, however, can't ;)
But looking at the raw data from that time there was quite a lot of heavy precipitation in the area - particularly to the Upper-Left of the crash site.

It's the former - and in some places the cell had busted several thousand feet above the tropopause.

Is it correct on an A320 that you only have 2 ELACs and 3 SECs? Which set contains the normal law intelligence?

There is a comment on another forum that uncommanded rudder is suspected. But even if the rudder was at full deflection could this not be counteracted and control maintained through engine power and aileron input?

Just a speculation then from information I have read about the flight computers, if there were multiple sensor failures, say the pitots iced up, you might expect automatic computer failover and ELAC 1 would fail over to ELAC 2, if there was a fault with ELAC 2 as has been suggested may be a possibility with the maintenance log, would you then be left with 3 SEC computers which have no aileron authority?

I don't have an argument with the tech talk about CVR audio freq analysis and filtering. It could be useful to decide if an alarm or other continuous noise has occurred.

However the real challenge is interpreting the words of the crew as spoken in their language and/or dialect. It's not just a fixed frequency question but a combination of sounds. Mess with that an you may never agree on the words in spite of the best guesses of "it sounds like"

Aaah, so that's why some posters ([3, 5[) have mumbled about rudder trim and stuff like that.

Well, I have been following this discussion here and no, only for those rudder trim guys noone have mentioned such gossip. But sure, this is for rumours too, as it says in the title.

Uncommanded rudder scenarios happened on a few Boeing 737's many many years ago. Hydraulic parts froze at altitude and when hot hydraulic fluid entered the part it jammed and caused a rudder hardover and even rudder reversal.

However all the scenarios where this happened were uneventful flights where the rudder all of a sudden slammed to one side and the plane nosedived straight into the ground. We are not looking at that kind of scenario here.

McWho
 

A320 roll control is provided on each wing by one aileron, augmented by four roll spoilers.

There is a comment on the same forum that a loss of flight computers can result in the uncommanded rudder deflection on the Airbus.

Thanks for the comment about the spoilers, I had not realised they could be used for roll control which would imply that the SECs can provide this control in the event of ELAC failure? I did read however that the ELACs were the only source of aileron control on the Airbus.

I fly the A320, and recently received guidance that when Sparky (the mysterious French brain that protects us from screwing things up) is directing unsustainable nose up or down auto commands, you press off two of the three ADIR push-buttons.

My bible is to turn off all the automation when things start to spin out of control. It will fly like an airplane if you allow it.

With experience (now about 10 years on Airbus), I've found, less and less do I question, 'Why is Sparky doing that?', as I know as soon as I ask myself the question.

One thing I inwardly shudder about, though, is that under the seniority system of the major airlines flying the A320, you can have the situation of a brand new Captain coming from an old Boeing with no Airbus experience, and a new FO who knows next to nothing, dealing with the surprises Airbus will throw at you.

Full rudder deflection at cruise speed can cause vertical fin separation. The rudder is sized to provide sufficient rudder power to overcome a worst case yaw deflection at or near stall speed. At cruise speed the rudder has enough power to fail the vertical fin. The rudder damper system is (usually) designed to prevent excessive rudder deflection at high speeds in a mechanical flight control system. In a fly by wire system that is taken care of in software. If something went wrong to cause a full rudder deflection at cruise, or worse yet rudder couplets (swinging the rudder at high deflection from one direction to the other) at cruise, the vertical fin will fail. That was the cause of the loss of AA flight 587.

YAW on A320
 

Yaw damper is designed to "damper" yaw movements not to limit rudder deflection. RTLU (Rudder Travel Limiting Unit) is there to limit mechanically the rudder deflection depending of A/C speed, this units (double) are driven by FAC's fonction of speed information from ADR's.

YAW
 

In fact, rudder is sized to cope with VMCG / VMCA. Easy to find what's VMCG/VMCA on the net.

Doesn't fit this scenario.
At all.
Uncommanded rudder trim would cause a nose down dive and a sharp turn. (Or possibly a fin separation again with a dive and sharp turn)
Here we have a massive climb and at a very wide turn until very late in the event.
So: You can probably scrap rudder trim runaway in this case. Doesn't seem to fit to what we know so far.

If boom mics are worn and designed to stay on during severe turbulance! they remain the best solution.
The overhead mounted ambient mics with an omnidirectional pickup pattern cant be expected to recieve the pilots voice clearly when pilot is looking at instruments and when the warning speakers are direct line of sight to the mic.

A couple of panel mounted directional mics each aimed directly at where the pilot and FO is looking could be considered if boom mics cant be relied upon.
This will reduce background level relative to voice level. These mics and the ambient mic could be fitted with wind gags to eliminate the sound of air moving over the surface of the mic, so called "wind noise" that would otherwise greatly reduce the fidelity of the recording during a decompression or other event.

Cameras that show the crew mouths will help with deciphering what was spoken.
I guess that cvr use compression? Use of high rates of compression when there is lack of control over mic placement and background sound and when level control is "auto" is to be avoided. Compression trys to keep every hum and background noise (there is considerable background noise of air over the fuselage) at the expense of reducing amount of data to record the good stuff.

As with images, the less control of the subject the more beneficial it is to have a high fidelity equipment, in this case microphones and a recording strategy which allows far more detail to be extracted post event.

A camera looking into passenger cabin would be very useful to evaluate passenger response to emergencies including evacuation.

Yes I agree with you it seems most likely that the sharp turn was induced as a result of the stall. However the bus is supposed to be spin tolerant when stalled even in gusts or asymetric thrust. At least they have the FDR to analyse fully on this occasion.

Nose dive
 

I am not an A man, so hardly dare to comment on the rudder behaviour. However, many years ago, in the early days of the 757, a slow L HYD leak required the system to be switched off until required for the approach. For some reason all our aircraft required a great deal of rudder trim in the cruise (later corrected). Having such a leak and following the QRH, the result was an immediate 30 to 40 degree wing down. The aircraft, though, maintained straight and level (altitude but not wings!) flight with us hanging in our straps until the L HYD was quickly switched back on again. There was no immediate nose dive at all. This was due to a full rudder deflection. Mr B informed us later that the ratio of rudder deflection reduces with speed by 15 times due to the RUDDER RATIO which, of course, was switched off by selecting L HYD OFF.

One of the best techniques to keep an undesired FBW pitch up from bleeding off all your airspeed is to immediately drop a wing and convert pitch-up into turn. The little bus will let you get 67 degrees bank if you hold the stick over, right?
It may be that QZ8501 was doing that but got started too late and bled off too much speed and fell off onto the low wing in a stall.

For someone who flies the little 'bus:
How long do you think it would take to turn off two of the 3 computers if you were surprised by an undesired maneuver? I'm betting that it would be about 15 seconds from initial startle to Alternate Law-and that only if you were really on top of your game.

The equivalent deflection ratio exists on the airbus apparently, the AP can command +/- 3 degrees of rudder deflection at high speed to +/- 30 degrees at low speed. When actuated any deviation from the track is compensated with opposing elevator and aileron but AP aileron authority is limited and under the fault conditions the craft cannot maintain track, manual control is required.

At first it seems surprising that the AP can command a rudder deflection that would defeat lateral navigation, but if you consider normal operation would be to compensate for weathercock due to high winds not compensation for a software anomaly.

Human performance in stress / startle
 

The sad but interesting parts of the CVR / DFR data analysis will be the human response to some of the alarms.

If, as in , say Colgan style, or AF, the PF response to stall was NOT nose down, due to startle or whatever, does there need to be in the alarm aural sequence, the loud and repetitive message "pitch nose down" announced ?

Although it it obvious and basic, it is clear in recent years that it is not automatically done. And if there are already aural warnings with ground prox saying "pull up" (mind you not helpful if aircraft in stall), by which stage the a/c is 3 - 5 seconds from impact, why not a message such as above which would be helpful, while the a/c may still be at salvageable altitude.

Of course avoiding getting into the stall is preferable in the first place.

Just my 2c worth as a pax with frequent interaction of stress situations.

mcloaked, you are welcome, hope it helps.

Its on tube as well : https://www.youtube.com/watch?v=gHf5XPO9wAA

The video shows what looks like a an A320 and cautions that air brake deployment may cause pitch up - is this true on the A 320?

aussiepax

I understand what you are getting at, but, believe it or not, if you are in a spin, in some planes, the nose is already down.

so, instead of saying: pitch nose down...it would be better if we all just PUSHED FORWARD ON THE STICK (control wheel or sidestick).

AND we should have learned this in our first lesson in a plane.

And Wolfgang Langweische, a great author of "stick and rudder" wrote about this over 70 years ago.

But you see, some smart ass somewhere said: oh, just ''relax back pressure"...and sometimes that is not enough.


So...here we are, 70 years AFTER
"STICK AND RUDDER" was published and we still don't get out of stalls right.

There is a good chance you will never have a problem...just ask your pilot : have you read, "stick and rudder"?