Air France crash? 2

[Higgler]

Now that pitot tube icing has been confirmed, were the pilots pulling up to slow their speed?

Why don't pilots carry an aircraft capable GPS with them in the cockpit to see their ground speed? I say aircraft capable because one pilot I knew bought a $120 GPS that had a software load which would not display speeds above 100 mph, just to make you buy the much more expensive $400 aircraft GPS.

 

[rb1957]

"Wings level, nose on the horizon and cruise thrust shouldn't get you in too much trouble"

but when your attitude indicator is telling you garbage, and you're trained to believe the instrument over your personal "attitude indicator", and you're flying at night over the ocean in a storm ...

what chance do you have to level the wings or point the nose at the horizon ? "old" planes had "stick free" stability ... do fly-by-wire ? and how does a flight control computer behave when it's getting zero input ? or inputs that are highly different (if it senses both pitots, and only one froze) ?

there was an accident out of Cuba, a B757 i think, where the pilot's pitot was malfunctioning ('cause a spider had made a nest in it ... you can't dream this stuff up !). i thought one of the conclusions of the investigation was the flight control computer should sense both pitots ... i think it was sensing only one. similarly why record only one ??

 

[thruthefence]

And while we are discussing occluded air data sensors, let's not forget the Air Florida Crash flt 90, January 1982 in Washington, DC.

In this case it was the EPR probes that iced up, making the pilots believe they were at takeoff power settings.

 

[LionelHutz]

It seems odd that they kept the plane nose up, especially after the speed indicators temporarily returned and indicated a substantial loss of air speed. The pilot must have pitch attitude and/or angle of attack indicators?

But then it also seems odd to me that applying power would be used to recover from a stall at those flying conditions.

The #1 rule in flying is: fly the aircraft.

I've always thought following this rule was a major factor in how Captain Sullenberger was able to successfully ditch 1549 in the Hudson.

 

[Higgler]

I read that all those (easily iced over)pitot tubes were replaced by improved units for all Airbus aircraft.

I know that GPS can be used for attitude sensing (<1 degree accuracy in pitch roll and yaw), maybe one should be added to aircraft as a simple backup system. GPS can be jammed electrically, so that is a hazard.

 

[MintJulep]

but when your attitude indicator is telling you garbage, and you're trained to believe the instrument over your personal "attitude indicator", and you're flying at night over the ocean in a storm ...

But I haven't seen anything that suggests that the attitude indicator was malfunctioning. To the best of my knowledge an attitude indicator does not have any connection to the pitot system, so it would be unaffected by pitot icing. But if I'm wrong here please correct me.

They seemed to be able to keep the wings level. With no visible references it's likely that they were using the attitude indicator for that. Or does the Airbus also have an old-fashioned turn and bank indicator too?

So why did they believe the attitude indicator for roll, but not for pitch?

 

[WKTaylor]

MintJulep ... see rule #1

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[thruthefence]

Correct me, anyone, but I believe transport category aircraft are required to have a stand-by attitude indicator system, as well as a stand by air data system. And I believe the anti-ice provisions of the stand by air data, (heated pitot & static ports) is on a separate circuit.

 

[moon161]

Continental/colgan 3407 was a case of the autopilot kicking out due to icing and aircrew failure to fly a flyable airplane.

http://en.wikipedia.org/wiki/Colgan_Air_Flight_3407

One thing that came out in the papers is that commercial/civil pilots are not trained to fly by AOA (military pilots are), nor are commercial aircraft IIRC equipped w/ AOA instrumentation. In aero class at least, it's all about alpha which tells you so much. Dunno how it's justified not to give pilots something so useful.

 

[CoryPad]

Here is an excellent thread that has lots of technical information regarding the questions raised here regarding conditions, equipment, procedures, etc.

http://www.pprune.org/rumours-news/447730-af447-wreckage-found-22.html

The link is for page 22, which is around the release date of the BEA report so the discussion is more about the known data rather than wild speculation from the past three years.

 

[Higgler]

After reading all the links, seems like automation is both great and deadly since people aren't ready for sudden failures in electronics.

Interesting that reacting to a stall has changed from priority of Increased Power to new priority of Nose Down. Although if you don't know your altitude, that can be scary (carry two personal GPS's, at least you'll have your altitude handy).

thanks for the links.

 

[thruthefence]

The point I was alluding to, eg Colganair 3407 was this:

(from the NTSB report)

"Unfortunately, instead of following the established stall recovery procedure of adding full power and lowering the nose to prevent the stall, the captain only added about 75% power and continued applying nose-up inputs. As the aircraft came even closer to stalling the stick pusher activated. The stick pusher is designed as a last ditch effort to lower the airplane's attitude to fly out of the stall. The captain overrode the pusher and continued pulling on the control yoke resulting in the upset and subsequent loss of control"

Which at first glance by a rank amateur, seems like is what was happening on the Air France accident.

 

[thruthefence]

A correction to my previous post; the quote was not from the official NTSB report, but from a comment the an NTSB spokesperson made to the media.

 

[debodine]

Just a bit of information that comes to mind after reading the latest set of posts:

Transport category aircraft do have a third attitude indicator to allow the flight crew to choose "best two out of three" on the theory that two of the three won't die at the same time.

Attitude indicating systems are not connected to the air data systems in any manner that should allow the air data system outputs to influence the attitude displays. Generally the attitude indicators link directly to the inertial platforms and any air data information in the attitude indicator system is normally only data passed to the indicator for display and cannot modify the basic attitude indication.

That being said, the Airbus series of aircraft do not have control cables where as a last resort the flight crew can ignore all system inputs and place the flight controls exactly where their trained instinct tells them to set the controls. What I mean byt that is while I am NOT a software expert, i believe in any fly by wire system somewhere, somehow an electronic circuit passes judgment on the pilot input and decides whether to allow, modify or deny that control movement.

So one possible scenario could be: probes ice over and air data inputs begin to change, causing flght control software to make decisions on what to believe and what not to believe, causing flight controls systems to accept/modify/deny pilot inputs based on the software laws.

Note that I am not speaking of the autopilot and autothrottle systems as those systems disengaged, presumably as intended by design when the inputs became unbelievable. I am speaking of the electronic systems that interpret the signals from the side yoke, rudder pedals and throttles to develop and send signals to the flight control actuators.

Note that I am neither involved in the investigation nor am I a trained investigator. Consequently feel free to take my input with a grain of salt, and you would not be out of line to tell me I am full of it if your knowledge of Airbus systems is greater than mine (which would not take much).

The biggest flaw in my scenario from the available data is that the recorded data shows the pilot flying deliberately applied nose up input, and there was no indication that what the pilot was commanding was refused or modified by the fly-by-wire system. I only present my scenario to note that (in my opinion) we have taken the flight crew too far out of the control loop and if I were a pilot I would feel much better if there were mechanical cables between my controls and the flight control surfaces. And I think that mindset is reflected in flight crews that don't seem to go back to basic stick and rudder with complex failures.

I would think that basic stick and rudder skills would dictate the Attitude + Power = Performance could have helped, but I don't know that flight crews today pay that much attention to it with all the eletronic systems doing the monitoring. Flight crews from olden days could normally recite "at this weight at this altitude I use this throttle setting and this attitude." In these new electronic aircraft I don't know if the flight crews do that nowadays.

Also keep in mind that I have hundreds of hours on the flight deck observing and interacting with flight crews, but that has not occurred for at least 15 years. Thus I have NO flight deck time on a fly by wire aircraft from which to draw conclusions. Just one more reason to write off my comments if they don't apply to today's flight deck environment. I confess I am rapidly reaching dinosaur status in aviation. )

 

[IRstuff]

"Attitude + Power = Performance"

Only when you're not stalled, which is what they were. Not that they were applying full power, though. They were falling at 10,000 ft/min for a solid 3 minutes because they were stalled out.

TTFN

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[SAITAETGrad]

wkTaylor, the AeroPeru accident came to mind as well. In that case, it was the static ports that were in error but in both cases you can imagine the number of simultaneous errors and warnings that would be going off. Unless the crew recognizes that they have an ADC issue, they would easily become bewildered. One could speculate that they were looking to do what they thought the systems were asking of them instead of troubleshooting the systems to take the correct action.

Watch the Mayday/Air Crash Investigation episode on AeroPeru 603:

http://youtu.be/pXTbseOEFdQ

 

[debodine]

IRStuff, you are correct. I should have indicated my belief that Attitude + Power = Performance may have assisted in keeping them OUT OF a stalled condition by not letting them GET INTO a stalled condition. The assumption there is that the flight crew would have known the aircraft to be flying fine just prior to all the confusing warnings, and thus would be loathe to start shifting the attitude and power until they could confirm departure from the previous conditions.

The B-52 crews I used to work with had a saying, "When you have multiple emergency warnings, break out the flight lunches". In other words, don't start making changes without thinking things through to confirm a genuine emergency.

But your point is very well taken that once they were in the stall, the equation Atitude + Power = Performance no longer had any validity at all.

 

[debodine]

SAITAETGrad I agree with your premise. From the perspective of the flight crew, the AeroPeru inicident where the static ports were still taped would have meant that the flight crew never at any time after the outside air pressure began to change (as the aircraft gained altitude) did they receive accurate information. Until they were able to troubleshoot and determine what was bad information and what was good information they probably tried to comply with the guidance the systems were providing.

I would see the major difference here as the AF crew had several hours of an airworthy, operational aircraft before the confusing warnings, and thus I would have expected the most experienced crew member at the moment (in this case the Pilot Not Flying as the Captain was off the flight deck) would have said, "Don't change anything until we sort this out". Obviously since the autopilot and autothrottle disengaged, the admonition "Don't change anything" should be interpreted to mean "grab the controls but maintain attitude, throttle position and wings level until we can verify a problem." The AeroPeru crew effectively NEVER had reliable information after liftoff.

But of course I am not sitting in a thunderstorm at night with a flight deck full of jangling alarms and the responsibility for several hundred people riding on my shoulders, so what may sound reasonable now was obviously hidden for the real players during their emergency. Otherwise they would be going about their daily lives today and remembering their close call.

 

[thruthefence]

" From the perspective of the flight crew, the AeroPeru inicident where the static ports were still taped would have meant that the flight crew never at any time after the outside air pressure began to change "

I disagree.

I wouldn't think the airspeed indication would respond in ANY normal fashion with the static ports sealed. I really don't see how how they would have known where V1 was on the roll (or any of the other takeoff critical "V speeds" published in the POH) in this condition.

 

[rb1957]

wouldn't the tape over the static ports retain the SL pressure ?

 

[KENAT]

That's what I was thinking. Then I started thinking about how static ports don't read true local pressure because of aerodynamic effects and how that might mess things up as you got faster.

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