BA038 (B777) Thread
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DO NOT keep F30
There has been a recent fresh rumour regarding new procedures issued from Boeing, I find that to quench a rumour in its' early days is vital to preventing it spreading and gathering momentum.
I was bewildered as to what was being said so checked it with a 777 trainer friend that I know to question its' authenticity. He flatly informs me that Boeing definitely DO NOT recommend maintaining F30 in this incident on the777..
'Cloud Bunny', I am sorry that I felt I had to question your post #2757'; but I know from what I've read and seen from Boeing that this shouldn't be the case on the 777. Of course I have no knowledge as to what would or would not be right on other aircraft (so I will not make the assumption that what is right on 777 is right on an alternative Boeing) as I only asked 777 trainers.
I was bewildered as to what was being said so checked it with a 777 trainer friend that I know to question its' authenticity. He flatly informs me that Boeing definitely DO NOT recommend maintaining F30 in this incident on the777..
'Cloud Bunny', I am sorry that I felt I had to question your post #2757'; but I know from what I've read and seen from Boeing that this shouldn't be the case on the 777. Of course I have no knowledge as to what would or would not be right on other aircraft (so I will not make the assumption that what is right on 777 is right on an alternative Boeing) as I only asked 777 trainers.
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That's an interesting point but it's just a part of a whole situation. Boeing might recommend to retract flaps from 30 to 25 but I'm quite sure IAS control and initiating a best-glide speed recovery will be the priority once the lack of thrust is being confirmed.
To understand this simply imagine that you're already configured flaps 25 when the failure occurs: speed control is obviously the most important task to perform.
Once again I'd be very interested to know what prevented the PF to revert to best glide speed earlier, at least once flaps 25 were selected. The fact that manual speed control was only initiated when the stick-shaker got activated looks like a passive and not an active decision. Why? Retracting flaps was one thing but speed monitoring and control should have remained the priority. What interfered?
To understand this simply imagine that you're already configured flaps 25 when the failure occurs: speed control is obviously the most important task to perform.
Once again I'd be very interested to know what prevented the PF to revert to best glide speed earlier, at least once flaps 25 were selected. The fact that manual speed control was only initiated when the stick-shaker got activated looks like a passive and not an active decision. Why? Retracting flaps was one thing but speed monitoring and control should have remained the priority. What interfered?
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Anybody have a picture from the cabin of the 777 flaps in landing configuration. While riding as a pax, I was amazed at how near vertical the inboard flaps appeared to be on final. Looks like huge amounts of drag to me. Wonder if a flap 15 position would have helped even more(if it exists). Hopefully will be examined in the report. Woder what the difference in ref speeds is between the various larger flap settings?
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SFLY
i do not like to repeat myself but pls see my post #2743 and mmm's explanation:
the reason to act manual ONLY AFTER the stick shaker was activated was to fly level as long as was safely possible to get closer to the airport area. Flying low angle approach and faced with double engine failure one have two options:
would you rather hard-land inside or outside of the airport perimeter? in case of fire what would be the time to get help from airport firemen in both these cases?
seems to be a no brainer to me - but what do i know
Once again I'd be very interested to know what prevented the PF to revert to best glide speed earlier, at least once flaps 25 were selected. The fact that manual speed control was only initiated when the stick-shaker got activated looks like a passive and not an active decision. Why? Retracting flaps was one thing but speed monitoring and control should have remained the priority. What interfered?
the reason to act manual ONLY AFTER the stick shaker was activated was to fly level as long as was safely possible to get closer to the airport area. Flying low angle approach and faced with double engine failure one have two options:
- fly quicker and land shorter - possibly long way before the runway and in this case higher speed would mean more fatalities
- try to fly as level as possible untill the last moment (stall alarm) and only then go for speed just enough to flare before touch down
would you rather hard-land inside or outside of the airport perimeter? in case of fire what would be the time to get help from airport firemen in both these cases?
seems to be a no brainer to me - but what do i know
Controversial, moi?
...the reason to act manual ONLY AFTER the stick shaker was activated was to fly level as long as was safely possible to get closer to the airport area.
They did not have the luxury of unhurried, logical analysis. They may or may not have been able to do things differently with better results but, given my guess they were overwhelmed by an impossible situation, the instinctive flap retraction was a gut feeling and saved the day, the late AP disconnect was a reaction not a planned action.
Why can't this pointless speculation cease and people just wait for the definitive account and analysis which will be published sooner rather than later?
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WojtekSz,
the conception you have on what's going on in flight is biased, try to fly as level as possible won't bring you anywhere, but keeping the speed is your best bet to reach somewhere, especially in case of headwind.
the conception you have on what's going on in flight is biased, try to fly as level as possible won't bring you anywhere, but keeping the speed is your best bet to reach somewhere, especially in case of headwind.
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CONF iture,
maybe i have been unclear of what i see as flying as level as possible - my fault since flying level flight was simply not possible without power!
i used the term 'flying level' as a short version of saying: to stay as close to level flight as possible with the existing plane configuration and airspeed, in order to achieve best horizontal progress with lowest loss of flight height.
It would mean most efficient use of whatever energy was available to get closest to the airport without stalling or loosing too much height.
The AP is surely not designed for such flying but looking at the data from Interim Report it was pretty close to optimum.
We are talking about possible optimization for the dirty configuration plane flying close-to-stall at some 300ft. Hardly possible to solve analytically. Not so easy to replicate in sim. The crew has successfully solved it empirically. What we are doing is analyzing what they did in order to identify possibilities for any realistic improvement.
maybe i have been unclear of what i see as flying as level as possible
- my fault since flying level flight was simply not possible without power!i used the term 'flying level' as a short version of saying: to stay as close to level flight as possible with the existing plane configuration and airspeed, in order to achieve best horizontal progress with lowest loss of flight height.
It would mean most efficient use of whatever energy was available to get closest to the airport without stalling or loosing too much height.
The AP is surely not designed for such flying
but looking at the data from Interim Report it was pretty close to optimum. We are talking about possible optimization for the dirty configuration plane flying close-to-stall at some 300ft. Hardly possible to solve analytically. Not so easy to replicate in sim. The crew has successfully solved it empirically. What we are doing is analyzing what they did in order to identify possibilities for any realistic improvement.
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Since the 777 has many different configurations, each one will have it's own best l/d and speed to fly, STF that will always be faster than the min/sink for that configuration.
I did find a nice animation on the Internet once which illustrating the differences between flying too slowly, at the right speed and too fast, but can't find it now.
There are a couple of Wikipedia articles which explain the theory:
http://en.wikipedia.org/wiki/Polar_curve_(aviation)
http://en.wikipedia.org/wiki/Lift-to-drag_ratio
However, my own view is that whatever the theory, MMM managed the situation well enough that everyone survivied and nearly everyone was (physically) unhurt. Will be very interested to see the final outcomes of the work going on at Boeing about handling this thankfully very rare occurence.
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Come on WojtekSz, achieving the best gliding distance is done by flying at best glide speed in the cleanest configuration (no flaps or ld gear) and certainly not by pulling on the nose till the minimum speed. When you have headwind you even need to increase speed over best glide speed. I don't know the best glide speed of the 777 in flaps 25, but it's usually very close to Vref.on many aircraft. The more you deviate from that speed, the more you shorten your gliding distance.
There are certainly many explanations for the late AP disconnection, but you can't seriously pretend it was intentional in order to extend the gliding distance as it's clearly achieving the opposite. Retracting flaps was not all as some people seems to believe, speed control is much more important in such situations.
There are certainly many explanations for the late AP disconnection, but you can't seriously pretend it was intentional in order to extend the gliding distance as it's clearly achieving the opposite. Retracting flaps was not all as some people seems to believe, speed control is much more important in such situations.
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Great reply Woodpecker...
..I developed senses and reactions which enabled me to pre-empt changing conditions on the 733, very much in the way you describe.
I know from mutual friends that Pete was a loyal BA employee, a pleasure to fly with and a true professional. Job done!
I know from mutual friends that Pete was a loyal BA employee, a pleasure to fly with and a true professional. Job done!
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I have always wondered whether bringing up the flaps to G/A configuration would have significantly changed the outcome, Vref 30 +5 being roughly the same as V2 flap 20.
( I write this as a retd 767 Capt with no experience of the 777). Has anyone done an in-depth analysis of various scenarios in the sim? If not it should have been done as the situation was outside any QRH action so walking away was a success whatever they did.
( I write this as a retd 767 Capt with no experience of the 777). Has anyone done an in-depth analysis of various scenarios in the sim? If not it should have been done as the situation was outside any QRH action so walking away was a success whatever they did.
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SFLY - i like your perseverance - so lets follow your suggested way and imagine we would like to fly best gliding speed ie closer to Vref
How could it be achieved (let us know if you see any other way):
I understand that we are talking about last 20 seconds of flight, right from the moment when the crew has realized that there is really no thrust available (some 3..4 secs after second attempt to add full thrust), with the speed already well below Vref (currently 115kt=59m/sec) and the nose quite high (8deg), clearly below intended GP (300ft=91m above ground), F30, gear down, ac weight about 200tons, with current vertical speed of 600ft/min(=3m/sec) - with this speed our max time in the air would be less than 30 sec:
so to reach Vref we need to accelerate the plane, the best way is to use some existing potential energy to gain vertical speed and than use wings to change it into horizontal speed: not to get into too much teory lets look how long it took and much speed was gained when finaly PF lowered the nose: within 8 sec the plain gained 1kt (sic) and the vertical speed has doubled ! If he would have lowered the nose more he would have gained more speed - but would he have time to get back to level flight?
SFLY be reasonable - would you really like to fly the plane using this strategy?
And look what the crew did: they used whatever kinetic energy was there to stay as high and for as long as possible. At the last moment they went for speed to regain ac maneuverability and just landed (not crashed).
Actually it is the same trick all young pilots instinctively try to do when get below ILS and forget to use the engine throttle
- so lets follow your suggested way and imagine we would like to fly best gliding speed ie closer to VrefHow could it be achieved (let us know if you see any other way):
I understand that we are talking about last 20 seconds of flight, right from the moment when the crew has realized that there is really no thrust available (some 3..4 secs after second attempt to add full thrust), with the speed already well below Vref (currently 115kt=59m/sec) and the nose quite high (8deg), clearly below intended GP (300ft=91m above ground), F30, gear down, ac weight about 200tons, with current vertical speed of 600ft/min(=3m/sec) - with this speed our max time in the air would be less than 30 sec:
so to reach Vref we need to accelerate the plane, the best way is to use some existing potential energy to gain vertical speed and than use wings to change it into horizontal speed: not to get into too much teory lets look how long it took and much speed was gained when finaly PF lowered the nose: within 8 sec the plain gained 1kt (sic) and the vertical speed has doubled ! If he would have lowered the nose more he would have gained more speed - but would he have time to get back to level flight?
SFLY be reasonable - would you really like to fly the plane using this strategy?
And look what the crew did: they used whatever kinetic energy was there to stay as high and for as long as possible. At the last moment they went for speed to regain ac maneuverability and just landed (not crashed).
Actually it is the same trick all young pilots instinctively try to do when get below ILS and forget to use the engine throttle
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WojtekSz, the funny thing between us is that we never understand each other. I'm sorry to say that you're conception of gliding and dead stick landing is wrong and dangerous.
Was you quoted was more a general/theory remark and I didn't say they should have dived to get back to Vref. My point was to say that speed control is crucial and if not increasing speed by diving, they certainly shouldn't have let it drop too low.
Maintaining best glide speed and retracting flaps is only the first step of a dead stick lading. When you get closer to the ground flaps can be selected (and speed finally reduced) to stretch the path in a long flare. But if you're not touching down at the end of this flare you just fall like a stone...
You said they were below intended GP, which is wrong, they were on the ILS GP which is above the best glide path.
Flaps were selected 25 some 20 s before AP disconnection, at 118 kts. I'm not saying they had time to accelerate to 135 kts and subsequently flare. I'm wondering prevented the AP to be disconnected at the same time flaps were selected 25, which would have given 20 more seconds to control a more reasonable speed (118 kts instead of 100 kts) at a much lower AoA.
Should the AP had been disconnected earlier the PF wouldn't had to make the nose down input you've mentioned. This was achieved because the aircraft was stalling. Keeping away from stick-shaker wouldn't require such actions. While I'm saying speed is essential it doesn't mean you have to accelerate when you don't have time, but disconnecting the AP simultaneously with the selection of flaps 25 would allow you to fly around 120 kts which is definitely increasing the gliding distance and giving a lot more of flare energy to control the impact Vz.
To me both actions on flaps and AP should come together, and I'm wondering why 20 seconds and 18 kts were lost.
By the way, lowering the nose by 1 degrees at 118 kts will give you much more acceleration and less Vz increase than at 100 kts... you just can't use this example to quantify the benefits of such inputs at different speeds.
Was you quoted was more a general/theory remark and I didn't say they should have dived to get back to Vref. My point was to say that speed control is crucial and if not increasing speed by diving, they certainly shouldn't have let it drop too low.
Maintaining best glide speed and retracting flaps is only the first step of a dead stick lading. When you get closer to the ground flaps can be selected (and speed finally reduced) to stretch the path in a long flare. But if you're not touching down at the end of this flare you just fall like a stone...
You said they were below intended GP, which is wrong, they were on the ILS GP which is above the best glide path.
Flaps were selected 25 some 20 s before AP disconnection, at 118 kts. I'm not saying they had time to accelerate to 135 kts and subsequently flare. I'm wondering prevented the AP to be disconnected at the same time flaps were selected 25, which would have given 20 more seconds to control a more reasonable speed (118 kts instead of 100 kts) at a much lower AoA.
Should the AP had been disconnected earlier the PF wouldn't had to make the nose down input you've mentioned. This was achieved because the aircraft was stalling. Keeping away from stick-shaker wouldn't require such actions. While I'm saying speed is essential it doesn't mean you have to accelerate when you don't have time, but disconnecting the AP simultaneously with the selection of flaps 25 would allow you to fly around 120 kts which is definitely increasing the gliding distance and giving a lot more of flare energy to control the impact Vz.
To me both actions on flaps and AP should come together, and I'm wondering why 20 seconds and 18 kts were lost.
By the way, lowering the nose by 1 degrees at 118 kts will give you much more acceleration and less Vz increase than at 100 kts... you just can't use this example to quantify the benefits of such inputs at different speeds.
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wilyflier:
your instructor was absolutely right!
the same applied possibly to your chemistry teacher who used to tell you: remember to pour acid into the water!
these are the golden rules which should be generally obeyed - especially by people who do not have the deep knowledge and experience.
As you would probably agree there are always exceptions to general rules, and these exceptions are being sometimes used to the user advantage.
And i am not talking here about speed limit being sometimes overstreched by all of us being experienced drivers
even if we all know that dangerous speed kills.
your instructor was absolutely right!
the same applied possibly to your chemistry teacher who used to tell you: remember to pour acid into the water!
these are the golden rules which should be generally obeyed - especially by people who do not have the deep knowledge and experience.
As you would probably agree there are always exceptions to general rules, and these exceptions are being sometimes used to the user advantage.
And i am not talking here about speed limit being sometimes overstreched by all of us being experienced drivers
even if we all know that dangerous speed kills.
Per Ardua ad Astraeus
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Originally Posted by wily
Pardon me, I still hear my instructor saying "Dont stretch the Glide"
It takes us back to the eternal 'Habsheim' argument as to whether an 'iron' a/c such as 737 would have had enough energy to just clear the trees without stalling unlike the AB with its alpha-floor protection which limited its climb = no trees, no crash..
There never will be an answer to that conundrum (and I am certainly not intending we should open this again!) nor to whether to trade speed for distance at some lower height. It all comes back to what I and Woodpecker described as that 'sixth sense or 'seat of the pants' which can only come with experience.
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i tried to compile my own answer to the problem presented by SFLY and when searching for B77 stall speed numbers i have found all the answers already there.
an executive summary:
some formal source to consider:
short thread just on the same subject can be found here http://www.pprune.org/tech-log/30928...st3852210.html
SFLY's problem was also discussed after D O Guerrero asked http://www.pprune.org/rumours-news/3...ll#post3845436
and got the answers among others from
Mad (Flt) Scientist:
eyeinthesky:
and moosp:
an executive summary:
FullWings: I think this discussion shows that you can't write SOPs for every conceivable occurrence and that Airmanship is thankfully still alive and well in some quarters.
Boeing 744 QRH: Procedures Beyond the Scope of the QRH
Introduction:
It is rare to encounter inflight events which are beyond the scope of
established non-normal procedures. These events can arise as a result of
unusual occurrences such as a mid-air collision, bomb explosion or other
major malfunction. In these situations the flight crew may be required to
accomplish multiple non-normal checklists, selected elements of several
different checklists (applied as necessary to fit the situation) or find little
or no specific guidance and need to rely on their own judgement and
experience. Because of the highly infrequent nature of these occurrences,
it is not practical or possible to create definitive flight crew procedures to
cover all events. (the bolding is mine)
Introduction:
It is rare to encounter inflight events which are beyond the scope of
established non-normal procedures. These events can arise as a result of
unusual occurrences such as a mid-air collision, bomb explosion or other
major malfunction. In these situations the flight crew may be required to
accomplish multiple non-normal checklists, selected elements of several
different checklists (applied as necessary to fit the situation) or find little
or no specific guidance and need to rely on their own judgement and
experience. Because of the highly infrequent nature of these occurrences,
it is not practical or possible to create definitive flight crew procedures to
cover all events. (the bolding is mine)
SFLY's problem was also discussed after D O Guerrero asked http://www.pprune.org/rumours-news/3...ll#post3845436
how does landing at very low speed or at the stall speed increase the glide? I thought the maximum glide distance would be achieved at best glide speed which is presumably quite a lot greater than the stall speed on a 777? And therefore that any speed either greater or lesser would only have the effect of reducing the glide distance. I don't dispute that the crew would have wanted to slow the aircraft as much as possible just prior to touching down - but I would have thought that slowing to stall speed in order to try and make the perimeter would be an extraordinarily bad idea....
Mad (Flt) Scientist:
You are correct that best glide speed is not stall speed, and an indefinite glide is best achieved at best glide speed.
However, gliding involves exchanging potential energy for kinetic energy (or, using a gravity component along the flight path to combat drag). If you were trying to extend a glide, and were, say, 500ft AGL, at say 1.3vs, you might be better off trying to use up some of the stored KE represented by the speed rather than simply use up that 500ft. Exactly what the best energy management would be is dependent on a lot of aircraft dependent factors, but hitting the ground at your lowest possible flying speed does ensure there was no wasted energy left which might have been used to extend the glide.
However, gliding involves exchanging potential energy for kinetic energy (or, using a gravity component along the flight path to combat drag). If you were trying to extend a glide, and were, say, 500ft AGL, at say 1.3vs, you might be better off trying to use up some of the stored KE represented by the speed rather than simply use up that 500ft. Exactly what the best energy management would be is dependent on a lot of aircraft dependent factors, but hitting the ground at your lowest possible flying speed does ensure there was no wasted energy left which might have been used to extend the glide.
Aircraft approach at a speed which gives them a margin above the stall speed (usually around 30% higher). In an emergency such as this, this 30% extra speed can be traded for height and therefore 'stretch' the flight path compared to that which would result from flying 30% above Vs with no power. It is a measure which has only a limited life, since once the stall speed is close the nose must be lowered again to prevent the stall. Then the aircraft is committed to where it will end up. It needs fine judgement and the failure to occur not before a certain point for it to work and the aircraft to reach the field. it would appear that in this case it worked, so well done to the teams aboard!
Unfortunately, there are too many crash sites in history where an attempt to 'stretch the glide' had insufficient energy (potential or kinetic) for it to work and the result was a wreck.
Unfortunately, there are too many crash sites in history where an attempt to 'stretch the glide' had insufficient energy (potential or kinetic) for it to work and the result was a wreck.
A colleague of mine flew several profiles on the 777-200 sim this morning (the real one, please, not the MS version) failing various engines at 500 and 300 ft on the LHR 27L model. A failure of 2 engines between 500 and 300 feet, with an attempt to stretch the glide towards stall speed produced a touchdown at a similar point on the visual model as the BA aircraft.
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A colleague of mine flew several profiles on the 777-200 sim this morning (the real one, please, not the MS version) failing various engines at 500 and 300 ft on the LHR 27L model. A failure of 2 engines between 500 and 300 feet, with an attempt to stretch the glide towards stall speed produced a touchdown at a similar point on the visual model as the BA aircraft.
- Attempting to stretch the glide won’t be obtained by bringing the speed towards stall speed, but by keeping the speed.
- Both engines were not failed but still producing some minimal thrust above flight idle.
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S.F.L.Y. - I'll say it again, you get it.
OK, for the sake of this argument let's presume that selecting Flaps 25 was the correct decision.
Who thinks slowing by from 118 kts Flaps 25 that they're INCREASING their gliding distance by slowing to 108 kts Flaps 25???
You're going from (approx.) Vref -20 to Vref -30. That's going to INCREASE your performance???
So, if you're on the back side of the power curve(lift curve/drag curve, whatever you want to call it in pilot terms) and slowing an additional 10 kts will INCREASE your gliding performance?
Another issue is that by slowing to AOA limits there is no excess energy(ie airspeed) to try and flare. That woud allow for a slightly decreased sink rate at impact.
OK, for the sake of this argument let's presume that selecting Flaps 25 was the correct decision.
Who thinks slowing by from 118 kts Flaps 25 that they're INCREASING their gliding distance by slowing to 108 kts Flaps 25???
You're going from (approx.) Vref -20 to Vref -30. That's going to INCREASE your performance???So, if you're on the back side of the power curve(lift curve/drag curve, whatever you want to call it in pilot terms) and slowing an additional 10 kts will INCREASE your gliding performance?
Another issue is that by slowing to AOA limits there is no excess energy(ie airspeed) to try and flare. That woud allow for a slightly decreased sink rate at impact.
Last edited by misd-agin; 10th Jan 2010 at 15:26. Reason: added sentence
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