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BA038 (B777) Thread

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BA038 (B777) Thread

Old 7th Jan 2010, 08:18
  #2721 (permalink)  
 
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Repeat Scenario

Mmmayday38

First of from an SLF thank you!

Secondly as I browse various scenarios and analogies of what is being said in various posts I would as a non technical person (humble SLF in awe)... ask this question.

Given your real life unique experience from which all walked away and god forbid it were to play out exactly the same, some day again in the future is there anything you would do different (as learned from this experience) which would have resulted in the outcome being even better than it already was?
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Old 7th Jan 2010, 08:50
  #2722 (permalink)  
 
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Fascinating discussion

We are very fortunate indeed to have Mmmayday38 contributing here - and it's very gutsy of him to actually spell out what happened and how he felt so frankly and in such detail. It's a real privilege to read his comments. Hats off to him.

We know that when the flap settings were changed by Mmmayday38 (at 240 feet) the autopilot was still engaged - so perhaps the move to Flaps 25 prompted the system to just tweak something somewhere to give the 777 just that tiny bit less drag to stretch the glide and gain those crucial extra yards.

Once the AP was disconnected though it was all down to human skill. ...But phew - it was right on the margin!
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Old 7th Jan 2010, 09:51
  #2723 (permalink)  
 
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Mmmayday38 thanks for your comments and I'm glad that you understand my point is not to blame anyone but to understand the mechanisms that lead the sequence of actions, wrong or not. We all are subjects to these mechanisms and understanding how and why we do things is very important.

I found this very interesting point in your comment:

I chose to leave my First Officer handling the aircraft to allow me to attempt to diagnose and fix the problem.
This is definitely how tasks should be split, my next question is why the manual aircraft handling happened so late (or what processed contributed to delay the AP disconnection).

WojtekSz's analysis is very interesting, but it is not totally correct to compare flaps 25 and 30 with constant AoA. However, the interesting point is to see how much of drag is added by deviating from the best glide AoA.

Provided that his numbers are correct, we see that between 3 and 14 degrees of AoA the drag difference is around 4.37. Maintaining the best glide AoA would not only save 3 times more of drag than the simple flap retraction, but also produce more lift (thus significantly increase the gliding distance and Vz control).
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Old 7th Jan 2010, 10:28
  #2724 (permalink)  
 
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Having done a few double engine failure on final scenarios in the sim,I think the reality is you are doing well if you get out a Mayday call and Brace Brace to the cabin.

Don't stall the aeroplane and keep energy for a flare.

I'm surprised at the Boeing recommendation to keep leave the flap alone too although I know that's the case.

If you are flying at Vref +5 the speed drops below Vref before the failure is even recognised in most cases. (B737-800 F30)

Better lucky than good and so much the better if you are both!
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Old 7th Jan 2010, 12:20
  #2725 (permalink)  
 
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Mmmayday38,
Just to say thank you for your post, I don't want to enter into the what ifs; flap settings, AP etc etc etc full stop.

On the day that this happened which I remember so well (living on the flightpath for ten years) knowing what 480 ft is when the problem occurred, and it was a 777 my thoughts recall the same words until this day, Those guys in the cockpit did a great job!
Sir, next time I have to SLF I hope you are in the left seat!

To quote again a PILOTS PILOT
By Rainboe: Those pilots saved that planeload with their quick thinking actions.
Yep they sure did!

Last edited by TIMA9X; 8th Jan 2010 at 06:53.
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Old 7th Jan 2010, 12:36
  #2726 (permalink)  
 
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What's the recommendation?

Quality Time; I am interested to know what Boeing are now recommending pilots/airlines to do if this scenario happened again please? If, for instance, on finals, with gear down and F30, final approach speed at 1500 ft and a double rollback occurred, or similar double engine failure; what are they saying to do? This would be twice the height of the BA38 incident. Are they saying the same for all wind conditions/runway clearways?

Wannabe Flyer; In answer to your question... We had the best outcome on the day, and I wouldn't change the decisions. I would, however, have appreciated more time; both to deal with communications, options and the fact that more time would have meant more height! I have seen the figures, and wouldn't want to end up anywhere other than the BA38s' impact point... no further forward, no further back! I'm not saying we briefed to put it down where we did, but, at the time it appeared to be the closest 'safe and unobstructed area' to aim for. With hindsight, my impact point appears to be the location that would result in the least number of fatalities.
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Old 7th Jan 2010, 16:52
  #2727 (permalink)  
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Excellent idea. It would save fuel as well. Had 038's GS been even slightly higher, with a 'below' figured in, no need for thrust to make the field. It seems to me a low GS is a margin that doesn't allow for minor drift below it. It is a hard deck. It also led the AP to seek a higher AoA. A long 3 degree is asking for fuel/waste.
 
Old 8th Jan 2010, 01:35
  #2728 (permalink)  
 
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Exactly the point, at some point allowing the aircraft to slow to 108 kts probably resulted in worse performance than maintaining Vref Flaps 30.

Quoting Boeing's recommendations probably has to be clarified or expanded. I doubt they recommend maintaining Flaps 30 if you're at 2000' AGL. At some point there's a tradeoff. Again, that's experience, experimenting in the sim, and a smattering of luck if you'd ever have to make that decision quickly.

Everyone's familiar with the drag increase at greater than Flaps 20. Getting to mid slats is key.

You can verify stall information for your a/c's stall speeds. First notch of leading edge slats typically is 50-60% of the total stall speed reduction. Additional flaps have a lot of drag vs. amount of stall speed reduction.
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Old 8th Jan 2010, 02:52
  #2729 (permalink)  
 
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As you increase flaps from zero, the L/D ratio decreases; i.e. you fly a steeper approach or you need more power to maintain the glideslope.

When there's no more power available and you're coming up short, you need to increase L/D.

Decreasing flaps does that, but you are also increasing stall speed; so, in a low energy situation with very few seconds to weigh alternatives, not decreasing flaps further once a survivable impact point has been achieved sure looks like the best way to minimise the risk of something else going wrong.

Mmmayday38 had to negotiate a tight squeeze between landing too short and increasing the stall speed too much; he looked out the window and did exactly what was needed
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Old 8th Jan 2010, 13:01
  #2730 (permalink)  
 
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These type of incidents are self evidently extremely rare. Therefore any change in aircraft or airfield operations to mitigate the risk must have pretty much zero downside in terms of safety.
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Old 8th Jan 2010, 19:26
  #2731 (permalink)  
 
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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.
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Old 8th Jan 2010, 22:42
  #2732 (permalink)  
 
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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?
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Old 8th Jan 2010, 23:04
  #2733 (permalink)  
 
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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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Old 8th Jan 2010, 23:35
  #2734 (permalink)  
 
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SFLY
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?
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:
  • 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
which method would get you closer to the airport flat grounds?
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
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Old 9th Jan 2010, 00:28
  #2735 (permalink)  

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...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.
You surmise.

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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Old 9th Jan 2010, 01:33
  #2736 (permalink)  
 
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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.
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Old 9th Jan 2010, 02:54
  #2737 (permalink)  
 
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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.
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Old 9th Jan 2010, 09:11
  #2738 (permalink)  
 
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Originally Posted by WojtekSz View Post
<snip>
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.
<snip>
The two are incompatible - losing height as slowly as possible and making best forwards progress. What you need is the second one - getting the best forwards progress. You fly at best L/D for that, and what that is will depend on the configuration of the plane and it's wing loading. However, it is faster than min/sink - losing height as slowly as possible.

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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Old 9th Jan 2010, 15:00
  #2739 (permalink)  
 
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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.
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Old 9th Jan 2010, 16:50
  #2740 (permalink)  
 
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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!
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