THS
 

OK, I stand corrected that the THS wasn't "stuck up". I recall a number of posts trying to figure out why it was up, and whether it was stuck, broken, etc. But it seems to have been up (for whatever reason) and stayed up. Has the BEA explained why?

RWA-

Amongst all the hot air generated on this topic, I think your analysis may pretty well hit the nail on the head. Unfortunately, a lot of people may not be seeing things in quite the same light. Quite a few posts ago, I made the comment that a very small pull on the stick at high altitude, if you were heavy and close to max altitude, (should'nt be there in the first place, especially if turbulence is present, as the FCTM clearly states), could put you in stick shaker very quickly, together with a zoom up into "coffin corner" territory, (don' t hear much talk about that phrase these days, do we!)

Combine that startle factor (for the unprepared/untrained) with a full up THS and you can see why a certain element of confusion may have arisen. I think we will eventually find there is more to this than simple pilot error. Not bashing Airbus, (they build great aircraft, and I speak from experience of operating the type as well as Boeing), but nevertheless Toulouse will have some explaining to do here.

Regrettably, over the years, Airbus have usually blamed the pilots in most accidents ("they did not understand the systems"), but then they quietly go ahead and change some bit of software/hardware.

The reason is simple. The pilot's nose-down inputs only reduced the elevator deflection a little - the elevator still stayed "up".

He didn't keep the stick forward far enough or long enough to move the elevator back to neutral, and then into the "down" position. The THS would only have started moving "down" again once the elevators were pushed beyond neutral.

The THS behaved exactly as designed.

Not wishing to sound facetious, but would you care to provide examples of where this has been the case any later than, say, 1994 (when the death of senior test pilot Nick Warner on a demonstration flight caused them to re-examine their priorites)?

Neither, importantly, did he exercise the option to re-trim the aircraft manually using the trim wheels, which would have taken significantly less time - presumably because he was not taught how.

Hi,

One from head is Mount St Odile (some changes after .. despite pilots made some mistake about descent rate settings if remember well) about interface

That might be how the system is designed to work but is it how a human "naturally" expects a system to work? Hasn't it been proven over the years that in an emergency we revert to how we expect things to work regardless of how they actually work or how we're trained to use them?

If I turn the thermostat up on my heating system I wouldn't expect the temperature to get hottor and hotter indefinitely.

If I turn the steering wheel of my car I wouldn't expect the turn to get tighter and tighter until the steering rack is on full lock.

Even the accelerator pedal on my car mostly behaves like a speed control rather than an accelerator. Once I have reached the desired speed I don't lift off the pedal to maintain that speed. I have to keep it pressed.

What other familiar systems have a "runaway" behavior like the auto trim?

puzzling...
 

One thing that is puzzling me is the speed of PF's hand on his movements aft and forward on the sidestick.
From 02:10:13 to 02:10:16 (only three seconds) he moved his sidestick 9 times. That's three times a second...
And with significant amplitude also.

What was he chasing?

The answer can be speculated from the BEA report.
When AP disconnected the a/c was pointed down slightly (Pitch=0 deg) and it was descending. Also altimeter might have jumped down a few hundred feet because of impared pitots and air temperature sensors due to a possible ice build up from the strom they were in.
Pilots are trained to maintain altitude in cruise so he correctly pulls the stick back to keep at FL350. It appears he was in a down draft because it took a large stick deflection to maintain altitude for a few seconds. At high altitude and speed his strong stick input has dangerous effects and a stall warning is triggered. He then notices airspeed is broken. We can speculate that he was distracted, took his attention away from altitude and tried to process what was happening. More errors occur further distracting him. Finally the a/c has risen to FL375 before he figures out he has climbed, he had exited the downdraft and had held the nose up attitude.

Climbing the aircraft without adding power results in a drop in speed. Same as a pendulum swing up. Now a/c was in a dangerous high altitude and low speed condition with impared flight controls (ALT LAW).

It didn't runaway. The pilot made such high nose-up demands via the SS for such a long time that to satisfy his demands the system gradually trimmed to full nose-up. If he'd relaxed the back pressure for long enough (ie. taken "standard" stall recovery actions) the trim would've moved back towards the nose down position. It just trimmed to try to satisfy what the pilot what was asking of it - a high nose up attitude.

No, but if you set the thermostat to a temperature that was higher than the heating system could achieve the temperature would rise to that limit. Similarly, the pilot was requesting a nose-up attitude that the aircraft, with it's low speed, couldn't achieve and the trim ended up moving to the nose-up limit.

Agreed. Look at the accelerations too.
Looks to me like he was over sticking then having to correct for each input.
Instead i imagine he should have used smooth gentle deflections.
Ever seen a nervous person drive a car like this? Constantly twitching the wheel having to correct over steer in each direction. A smooth small input is all that is required. I have also seen people use accelerator and brake in the same way, constantly pressing one peddle then the other. Instead of just calmly pressing accelerator to desired speed. You are pulled back and forwards in your seat. Can't say i've seen that behaviour much in pilots.
Totally speculative - is this consistent with anxious/un-trained behaviour from the onset.

In alternate law we are still in load factor demand correct?

Could be a passenger was flying it while waiting for the toilet? Or could be an instrumentation or recording error ;)

Flickering Flight Display
 

xcitation, it looks to me that he is "chasing" a flickering PFD.

It was an attitude indicator, because he is correcting roll also.

But anyway, at least to my knowledge, the normal is to be "quick" on ailerons and "easy" on elevators.

The graphics show the opposite.

According to the docs ALT1 / ALT2 have Load Factor.

That was in 1992 (2 years before the cutoff date I specified), and interestingly was the occasion on which the BEA invited the NTSB over to perform a co-operative investigation in order to prove they weren't trying t oprotect Air Inter or Airbus.

(The fact that Air Inter specifically ordered A320s with GPWS deleted didn't help in that case either)

One thing that is puzzling me is the speed of PF's hand on his movements aft and forward on the sidestick.
From 02:10:13 to 02:10:16 (only three seconds) he moved his sidestick 9 times. That's three times a second...
And with significant amplitude also.

What was he chasing?

__

I've flown with a few FO's that did that all the time hand flying. They have plenty of experience but don't seem to trust themselves hand flying so keep doing PIO's to touchdown. You would think some hands on flying would stop this but a lot of airlines discourage hand flying these days. The PF in the AF447 crash didn't seem to have a clue when the automatics failed. They need to look at the Bob Hoover you tube flick where he pours an iced tea pitcher into a glass while inverted in a roll in a Shrike on page 83 of the tech forum. I know Bob and he knows how to fly an airplane. He will be at Reno at the air races in mid Sept.But he has retired from demo flying.

Dozy
So what are you implying?That there was conspiracy to deceive and obfuscate prior 1994 but everything 's been above board since?

Would you say there are any latent dangers in this autotrim design in abnormal ops or that the pilots always instantly and intuitively recognize the transition from auto to manual?

Would you say that the stall inhibit below 60 is excusable in design terms as its outside the realms of probability?

Would you say that the SS is ideal in a multi crew environment especially when considering scenarios where stick input must be timely and CORRECT(stall/x-wind/sev turb etc)?They have the stick in fighters but thats one man.Why did AIrbus employ it in commercial airliners?To be NEW?You seem to be an avid Airbus apologist so I'd like to know.

Do you have an opinion on why BEA withdrew the stall logic recommendation(factors affecting safety can and must be included in initial/interim reports but maybe theres a valid reason)?

Do you have an opinion on why no mention was made of the Captain's decision to leave the cockpit even though he now appears to have known that weather was up ahead?

Hi Rananim, long time no see... :)

Not at all. They were overconfident in the abilites of their systems prior to 1994, that's for certain - and as such predisposed to put things down to pilot error when interface issues should have been looked at (the dual-mode Vertical Speed and Flight Path Angle in the Honeywell FMC being a major case in point, but the same computers were used in other manufacturer's aircraft). Airbus weren't alone in trying to point the finger at pilots in the '90s - Aircraft manufacturers are billion-dollar corporations open to massive liabilities claims and as such their legal departments will tend to demand it - look at how Boeing tried to pass the 737 rudder PCU issue off as pilot error until the NTSB had the "eureka" moment and tried a thermal shock test.

My honest answer is I don't know, but the fact is that the inputs made to the system were way in excess of any input that should have been applied at cruise level. As (I think) PJ2 says, manually controlling the Airbus via sidestick at altitude requires light thumb pressure in pitch, and gentle lateral movements. This guy wasn't taught how to handle the thing, so he's bashing it on the stops.

I wouldn't say anything other than that design tends to happen at the limits of what is known. I definitely think the logic needs looking at, but I find it difficult to be too hard on the aircraft and systems designers for not contemplating what would happen if the aircraft lost all speed data and ended up in a mushy stall due to overcontrolling. For all we know the stall warning on other modern airliners has similar inhibit modes, and I'm sure Airbus will share whatever information they have in that regard.

For a start, I am an apologist for no-one, see my earlier post for further details there (should only be a page or two back [EDIT - http://www.pprune.org/rumours-news/4...ml#post6622053]). Secondly, if you're going to start an airliner design from a fresh sheet, why not? Yokes can be a pain in the ar*e, and have noticeably been used as a crutch in certain situations (some of which happened after the A320 was well off the drawing board) when they had been effectively rendered completely useless. Sidesticks are smaller, lighter, de-clutter the flight-deck, allow more freedom of movement and the lack of backdrive makes the system less complex (technophobes don't even want to *think* about the numbers of lines of code required to make the B777 yoke behave like the old-school ones). It would also appear that the majority of people on here who have an issue with the sidestick have never used one. Neil Armstrong certainly didn't have a problem with them...

Presumably to clarify what the situation regarding stall warning actually is. This is an interim report after all, so let's wait and see what the final report says. I have a strong suspicion that stall warning logic is a complex beast that's going to need to be looked into by all manufacturers. Stall warnings and pilot's responses to them have been a prickly issue since at least 1972 and the BEA548 Trident accident.

Not at all, other than from a layman's perspective (in airline pilot terms) it appears that AF has a few CRM issues it needs to address if it hasn't already done so, but primarily, I believe that placing two F/Os in the flight deck - in the ITCZ at night notwithstanding - when neither of them has had any high-altitude manual flight training is frankly inexcusable.

From the BEA site (french)
communiqué 3 août 2011

Google site translation:
Google Vertaling

Transcrypt of press meeting is also now available (english)
Transcript de la conférence de presse du 29 juillet 2011

If the PNF had a yoke in front of him flailing all over the place mostly in his lap don't you think he would have responded and put it where it was required to be for the no airspeed situation? I know the yoke costs money and weight but isn't it a wonderful way to see what your fellow pilot is doing? Maybe Airbus should put yokes back in their aircraft.

What the lawyers lawsuits are going to cost them negates all the years of SS controls to reduce weight and cost.

This could happen again.

Recovering a Cessna 152 from a students stall is easy with dual yokes. It would be more problematic with a side stick of Airbus design.