Posts about: "FBW" [Posts: 34 Pages: 2]

Full suite of typical FBW flight envelope warnings and protections from initial "Airspeed Low" EICAS caution to inability to trim to autothrottle activation and pitch down, stick-shaker at onset of stall etc.

But nothing can protect against laws of physics that apply when there isn't just enough energy for a (possibly) shortened takeoff distance and misconfigured aircraft.

Very sad, and bewildering.

Airbus FBW will give you alpha lock where the slats won't retract if the AoA is too high or the airspeed too low.

​​​​​​​You do understand that the B787 is FBW right? You understand what that means..

what does that mean? Can still stall any Boeing. But don\x92t need to be in a full stall to lose lift and crash. Look at Asiana. Not much point pulling through the stick shaker! That\x92s max lift. And it\x92s hard to do as out of trim.

Many years ago when Fly By Wire was first being installed into aircraft they would show these amazing test flights where a pilot would pull back the throttles, raise the nose to try and stall the aircraft and the FBW system would lower the nose, add back in the power and keep the aircraft in controlled flight. That for me (an uneducated layman) was the point in FBW. It was safer than a pilot alone.
How is it then that a modern FBW aircraft can allow itself to be placed into a low, slow and high AOA profile which inevitably leads to a crash and appears to to nothing? I would have expected that the systems would have deployed anything needed, retract anything not needed or at least push the nose down?

1. Boeing FBW is different to Airbus FBW
2. No FBW can overcome the laws of physics.

My understanding is that Boeing believes that it\x92s better to allow the PF to fly right to the edge of a stall and provide ample warning that a stall is imminent. Airbus believes that it\x92s safer to never allow a stall, even at the price of limiting the PF\x92s ability to maneuver right to the ragged edge. Obviously (AF 447) that doesn\x92t always prevent stalls either.

Intriguing: agree it doesn't look like an inadvertent flap-less take-off, but having watched the video several times, I can’t see any sign of a pitch-down input (ie, less pitch up) that would surely be evident following a dual engine failure. Even if the loss of almost full power from underslung engines didn't naturally cause a change of pitch (FBW), surely the first instinctive control input following such a large loss of thrust would be to lower the nose a little.

Conversely, the rapid sinking feeling induced by the inadvertent Flap retraction at the Gear-up point could confuse the senses and be interpreted as a loss of thrust?

Tragic whatever the cause; I’m sure we'll have the answer fairly soon.

Trust that you are refeering to the A320 Hasbsheim crash (not Paris) that occured as part of an air show at the early days of the A320. If the case then likelyhood is that the cause was due to the Pilot willing to impress the attendance with a low pass / low speed manouever above the airfield (thus disabling the Alpha Floor protection) but not being used to / taking into account the FBW delay brought between moving the throttle and gaining effective thrust. 136 people were onboard. 3 died and 36 were injurred. No computer glitch there.

Can I just clarify: the 787 has FBW and certain flight envelope protections. If the pilots suffered a dual engine failure after takeoff, they would pull back to stretch the glide as the computers will not allow the aircraft to stall. This is effectively what Sully did when he kissed it into the Hudson like a pro.

In any other aircraft, if you lose thrust in all your engines, you would be pushing the nose down immediately!

I'm really trying to resist engaging here, but anyone who states what pilots, 'would', do in a given situation, simply hasn't grasped the most elementary, 1.01, fundamentals of human behaviour.

Again and again, I've listened to CVRs, or looked at FDR plots, or sat next to people in a flight deck or crew room, or restaurant, or anywhere (but especially in the back of a simulator)... and pondered what on earth led competent individuals to do what I had just witnessed. Of course, if the individuals aren't competent to start with (and that is NOT directed at this crew, but embellishes my point) there may be less mystery.

Also worth remembering, for those of us who do, the ludicrous training delivered by Airbus on the A320 family at the start, when they told people that, (a) pulling the stick back and holding it there will save you, and, (b) you don't need unusual attitude training in an FBW aircraft. I think we know how that played out. I'll add an element of my briefing for a departure in a single-engined aircraft, if a forced landing was not an option (eg Rochester, Biggin Hill), which also covers what I have always thought I would do faced with total power loss in a bigger machine, 'I will manoeuvre the aircraft to hit the softest thing I can, as slowly as possible'. Very glad I never had to see that through.

Regardless of FBW on the Boeings the pilot can stall the aircraft. The 787 and 777 don't have hard protection like the Airbus. You will get force feedback as you approach the stall, but keep pulling on the yoke and the plane will stall.

Which is why the aircraft flew a very sweet descent, nose up, increasing pitch until the Stall.

I still don\x92t understand the flap retraction theory

It happens- in every airline in the world, ask any of their training/FDM departments. There are reported incidents of it from almost
Every major airline I can think of. Humans are incredibly fallible, I\x92ve spoken to a captain who did this on the 737 back in the day (now flies Airbus) and on that day he caught himself. He said in the debrief after the flight he could not explain why he did it, absolutely no clue.

The issue I have is why one of the most modern aircraft in the world, a thoroughly 21st century clean sheet design with every protection under the sun would not have the adequate protections or performance to deal with this scenario. Surely the 787 has high AOA and low speed protections- those engines should\x92ve been screaming at TOGA LK (or the Boeing equivalent) and the pitch should have been limited regardless of the weight, density altitude etc

Airlines and manufacturers will always try and blame the pilots but I would be truly shocked to learn a FBW aircraft (Boeing or not) designed this century could get itself into such a catastrophic state so innocently. We KNOW many crashes have been prevented by Airbus FBW protections (a few Wizz examples come to mind

I’m not a 787 driver so for fear of looking dumb in front of those that are this still confuses me. Even IF they’ve mis-selected the flap setting (I still don’t think it’s been cemented on here that there is in fact a FMS/flap setting disagreement warning but i believe there is), had the wrong de-rated take off settings, selected flaps instead of gear up the 787 with massive high bypass engines, FBW and full envelope protections surely cannot let itself be put in such a low energy/high alpha regime as we saw in the videos IF it has both fans functioning normally, surely?

the pilots may have messed up royally and numerous times so those holes lined up but the plane is the final block in the chain and a 21st century all digital entirely clean sheet design was sold as being immune to such catastrophic outcomes from a few minor (consequential yes) and fairly common errors- aren’t all the protections and our procedures designed after decades of mistakes?

im having a hard time squaring how a fully functioning modern bird like this could allow for this outcome and almost whatever the pilots did outside of unbelievable inputs and the pilots are are a bit of a red herring IMO

also to add, if it turns out that this was triggered by some procedural slips from the crew, if I was an airline I\x92d seriously consider my fleet choices going forward. I\x92ve never been on the anti-Boeing bandwagon, that has been the refuge of many ignorant people over the years, but I struggle to believe an Airbus would\x92ve got itself into that situation and we know for a fact they with their protections (narrow bodies mostly) have saved multiple crews (and their pax) in recent memory. The most modern Boeing around was meant to be as safe as possible and redundant

I don\x92t agree with either of those assessments at all. One strongly pushing the flap scenario and the other a software fault. The flap one has been done ad nauseam, I won\x92t repeat it. A sudden software glitch on a decade plus old model is a stretch and likewise a call to ground the entire fleet immediately.

of course like everyone else I have absolutely no idea what actually happened but I am willing to bet the explanation will be simpler than everyone is expecting.

I am not going to speculate further as I believe it is a waste of time without further information.

For the record I am not b787 rated but I do have Boeing and airbus narrow body and wide body time and i struggle to forsee a situation where the aircraft falls out of the sky at 200ft without a very serious error of some description.

Are you thinking of a B787 which does not have FBW? Admittedly C* is not quite as tidy as C*U when it is working normally, but B777 and B787 systems do a darn good job of removing thrust-pitch couples (well, adequate).

Dont follow that logic at all\x85 this flare in the last second or three wasn\x92t IMHO to stretch the glide but reduce vertical impact speed.
sully flared almost perfectly, nothing to do with \x91stretching\x92 the glide.

The video is suitably clear to show that one engine DID NOT lose thrust before the other engine. The yaw rate authority in the FCS is going to input rudder immediately a failure of an engine occurs, (the 787 asymmetry architecture is quite different to the TAC on the B777) and so a rudder deflection would be evident. The video from the rear is ideally positioned to show a rudder deflection, and one would have been required, or a roll would have eventuated. Being FBW, the ailerons and asymmetric roll spoilers would be actuated to maintain the aircrafts attitude without any input by the crew if there is no roll rate command given by the control column (this is slightly different to the B777 as well).

The Thrust Control Malfunction Accommodation TCMA shuts down an engine when an idle asymmetry is detected . On the ground . With thrust levers at idle . The engine in question triggers the condition when it is above idle and not decelerating normally . That is multiple failure conditions that need to have occurred in the system to allow that to occur. It is nearly as wild a circumstance as the QFA 072 suspected cosmic bit flip, except that these are supposed to be independent systems. This does have the authority when the conditions exist to turn off the noise. That is the only reason it is a subject of interest.

The Thrust Asymmetry Protection gives a limited authority to reduce thrust on the surviving engine to maintain control. It would not trigger the conditions that the engines have gone silent, and hydraulics/electrics have been mussed up. That puts a spotlight on what has to go wrong on TCMA to get it to trigger outside of the conditions that it is intended to.

No yaw input, no roll input, no asymmetry. That leaves either both engines running at normal TO thrust or both having a simultaneous bad day out. Giving car keys to HAL 9000 can have some issues, and cosmic radiation is around a lot.