Having no experience on this type or indeed any FBW aircraft I have no idea of the relative "feel" of the controls A/P engaged or disengaged. Given the situation they found themselves in , I don't find it too surprising that they could have missed this, assuming the control feel is similar. On something like a B737 it would be fairly self evident , as the controls (even in CWS) do not feel the same, and anyhow the aircraft would have wandered off on a tangent, but with FBW, gust alleviation, and all these other boxes of tricks between you & the hardware ? perhaps someone experienced on type can tell us.
Well if you for some reason are trying to manhandle the controls on a triple with the A/P in you'd certainly notice, in the same way as if you tried to manhandle a 747 with the A/P in ( the 777 I fly doesn't have CWS, is it even an opton?). In my experience you only really notice the fact that the 777 is FBW if you get close to the edge of the envelope ( in the sim I hasten to add), when the various protection features start to kick in. Otherwise it behaves and feels like a conventional aircraft...then again of course it does, it's a Boeing
I cannot help feeling that the greatest omission from the accident report was the failure to thank our contributers for their selfless and assiduous devotion to providing the investigators with the detailed advice borne of PPRuNe experience without which the document would doubtless be short and lacking in substance, which oversight will, I am sure, be corrected in any future publication of the report.
Can someone give me an idea of the inside diameters of the fuel piping in question here? Having read the entire thread as well as the accident report, I don't see where it's mentioned (though I'm ill at the moment and may have missed it).
on a MD-11 for example, if you are on a 2 Engine approach and loose a second engine on short final, one of the Memory Items is to raise the flaps from 35 to 28. In my experience, changing the flaps from a intermediate approach setting to the final landing flaps, has more to do with stabilizing speed and power by increasing drag, whereas lift changes not that much.
So IMHO the BA did absolutely the right thing by raising the flaps one notch. Lift (and induced drag) would have changed relatively little - rather the parasite drag reduced.
The crew were being faced with something they were not really trained or prepared for - especially at the end of a tiring long haul flight. Everybody walked away. I have the deepest respect for the BA crew, ATC and the rescue services.
BT
Last edited by Burger Thing; 9th Feb 2010 at 17:41.
The lift drag benefit can be examined by checking stall speeds. On every airliner I've checked(6 types), the first notch of flaps reduces stall speed by 50-60%.
Obviously the greater the deflection the more drag vs lift is created.
Any old school fighter pilot can tell you about the value of leading edge devices. "Hard wing" wasn't your friend in a turning(ie high AOA) fight.
The flap retraction was done 115-118 kts(I've seen/recall different numbers). If the 777 would allow it there's a chance that a retraction to Flaps 20 at those speeds could have triggered a stall. I have to believe, based on Vso multipliers, that the AOA would have been mucher and I'm guessing it would outweight any configuration drag reduction.
I'd believe that an immediate retraction to Flaps 20 at Vref might be the best plan. Sadly, the AAIB report doesn't give the next guys any knowledge.
How quickly can guys be expected to react? With training and awareness it could be done fairly quickly. How quick does a trained pilot apply rudder with an engine failure?
For non pilots the difference for most Boeing a/c(that I know of) and I'm assuming Airbus' Flaps 2 is that the leading edge slats are in the mid, or takeoff, configuration. Most single engine configurations are based on mid/takeoff slats to reduce the drag associated with greater flap extensions.
My previous post explained how the largest stall speed reduction occurs in the first flap position(Flaps 1, Flaps 2, Slats EXT, etc). The last flap settings are just the opposite, mostly drag, with little stall speed reduction.
That is also why, as Basil mentioned, Flaps 20 is an important step in reducing drag, with a relatively small stall speed increase, to allow the a/c to accelerate rapidly during a go-around.
Ah, brings a smile to my face. Learned his concepts, didn't all G pullers, before I read his book.
I love telling Marines that I have great respect for their branch of the service, especially since they so willing put a statue of a USAF fighter pilot in front of their leadership school. "B.S.!" is often the internal, and sometimes external, reaction.
How quickly can guys be expected to react? With training and awareness it could be done fairly quickly. How quick does a trained pilot apply rudder with an engine failure?
This is certainly why Boeing issued recommendations on monitoring automated approaches which insists on mandatory manual override as soon as an automatism default is identified.
Retracting flaps from 30 to 25 improves the aircraft L/D "global" configuration, but you still need to fly the right speed to get the best of this new configuration. Flying best L/D speed at flaps 30 will take you further than flying minimum speed with flaps 25.
It's exactly like on a go-around: retracting flaps is improving the aircraft global aircraft config but you still need to fly the right speed to get the best GA performances.
In this particular case the captain's decision to retract flaps reduced the poor gliding performances resulting from flying at minimum speed.
The report clearly demonstrate that it was better than doing nothing, but it sadly fails to show what would have been the benefits of controlling the airspeed.
Safety Recommendation 2008-047 It is recommended that the Federal Aviation Administration and the European Aviation Safety Agency, in conjunction with Boeing and Rolls‑Royce, introduce interim measures for the Boeing 777, powered by Trent 800 engines, to reduce the risk of ice formed from water in aviation turbine fuel causing a restriction in the fuel feed system.
it goes onto say...
In addition, an engine response non-normal procedure was added to provide a procedure should the engine fail to respond to a thrust application. The procedure called for the thrust levers to be set to idle for 30 seconds, after which each engine thrust lever is moved to max thrust to ensure the restriction has cleared.
oh.... 30 seconds....? erm like you have 30 seconds to wait when your are 450' AGL at 108 kts and both engines no longer have any ooomph in them and the staff car park badges in the windscreens are easy to read hmmmm...
phil gollin
I'm amazed. I find the report extremely annoying.
I'm not and I don't. I believe the AAIB's report to be well researched, well written and comprehensive in scope. I believe that they have reached the right conclusions and have provided sufficient analysis to justify those conclusions. For those of us with more than a passing interest in fluid dynamics, more detail would have been gratefully read. But one has to draw the line somewhere, and I think that they have got the balance of the report just right. It is a QED report in my view.
Concerning the flap retraction, some would do well to read Capt P Burkhill's thorough explanation of his feel for the 777. Non believers can do the numbers or get someone to do them for you. Or just believe the AAIB. A difference of 51 metres is significant, and life saving in this situation. He obviously had no time to do the numbers; he knew from experience and instinct. A good man.
Anyone baying for the CVR, forget it. The crew probably swore, said good-bye to their loved ones, before they knew they were going to make it. What do you expect?
About the fuel restriction, I can understand that some might be surprised by this and may have a preference for other theories; others may accept it, but doubt the AAIB’s reasoning. This too is entirely understandable and normal. Water occurs naturally in fuel (from the atmosphere), on the ground and at 30,000ft. There is nothing new about that. But fluids can be tricky, especially water, and get trickier with changes in temperature and when ‘piped’. Anyone with an intimate knowledge of Fluid Dynamics knows that. That is why the AAIB were able to focus on this, and why myself and others suspected the fuel delivery architecture some time ago. AAIB, Boeing and Rolls Royce all accepted that a modification of the FOHE was needed, and I understand the all Trent 777 have now been fitted with modified FOHEs. So that's it.
That report will prolly be read by a wider audience than the official version and of course it is an interpretation. It has pics and good precis and is objective.
For people like me it is wunnerful because I can see the parts and understand what went on. It makes sense.
I don't think this will happen again due to the modifications made as result of this accident. That is all I seek. The outcome is postive and the world is safer..whatmore could anyone want?
Anyone baying for the CVR, forget it. The crew probably swore, said good-bye to their loved ones, before they knew they were going to make it. What do you expect?
Instead of swearing some crew communication could have helped to detect that the AP failed to be disconnected as it was believed.
I'd believe that an immediate retraction to Flaps 20 at Vref might be the best plan. Sadly, the AAIB report doesn't give the next guys any knowledge.
Aerodynamic basics would state that there is no set "rule" you can derive. The higher you are, the lower the optimum flap setting would be. As you get lower the lower stall speed with more flap outweighs the drag.
It is not the AAIB's job to (re)write handling manuals:
Quote:
The purpose of the AAIB is:
"To improve aviation safety by determining the causes of air accidents and serious incidents and making safety recommendations intended to prevent recurrence"
...It is not to apportion blame or liability.
Chief Inspector
They went as far in this report to analyse the FC actions as were relevant to the accident - in short, a no notice untrained for emergency, and their actions pretty much resulted in an optimal outcome:
Quote:
...they kept the aircraft flying and under control so that, at impact, it was wings level and at a moderate pitch attitude
Fundamentally this is a design/engineering accident, and little to learn from the FC pov - IMHO it is impractical to expect "drills" to be produced for every eventuality - especially since in this type of accident they would need to be "memory"...
There is basically no difference when this happen during an approach, there is no need for a "special" procedure. I regret that the AAIB didn't consider including few lines about it.
Instead of swearing some crew communication could have helped to detect that the AP failed to be disconnected as it was believed.
which will, no doubt, bring down the wrath yet again of the god-like pilots on poor old sfly. But, people, she has a point. Throughout my reading of this thread I've been amazed by the pure coolness displayed by these guys in leaving the a/p engaged until it tripped at stick-shaker. What faith in automation!
and now it turns out the F/O "omitted" to disengage it. That doesn't sound like a deliberate (and oh so cool) action.
And surely you guys out there see the point. Might it have been better to hand-fly from the moment the problem was identified? Perhaps not. Certainly the outcome could hardly have been better. But I think we'd all like to know.
SFLY 95% of pilots will follow the flight director if flying manually. The flight director will be trying to keep the aircraft on the ILS, exactly what the AP was tryting to do. So why increase the workload, when trying to faultfind an emergency for which there is no drill. For the 15-20 seconds that elapsed between when the FO intended to take out the AP, and when he did, the difference in flight path is hardly worth talkingabout, if you want something pointless to contemplate, why not have a heated debate about whether they should have asked all the passengers to move to the back of the aircraft, in an attempt to reduce control drag!
