Yes, slats do appear (visibly) to increase wing camber as flaps do.

However, their predominant effect is (and always has been) to re-energise top-surface flow at high incidences due to the slot effect (when otherwise it would be breaking down)

It goes back to basics in the heat of the moment, ie.

Stick Shaker = Stall recovery = full power, lower attitude

Its not a scenario that I have ever had thrown at me in a sim at that phase of flight ....

I would imagine initial reaction of crew is that they have used the wrong figures as a mass of red appears on the speed strip.

Out on a limb, no problem. The LE slats accomplish an extension and droop of the leading edge of the a/c wing. The extension widens the chord, the droop increases the camber. This is obvious, what seems to be at issue is the function of the "holes in the area left open by the slats". Wiki tells us the holes are the critical gain of the mechanism. I disagree. An aside: Wiki is bollocks in many ways, sit on it with caution.

Further, I'll introduce the concept of the "Blown" wing, to illustrate why the holes are not the deal, this time it is the cheese. See NASA's QRSA, an interesting experiment in short field performance. After reading up on the QRSA, think of the slats leaking underside airflow upward and see if you think the concept is what applies to slats. As air flows into the leading edge of the slatted wing, more will flow over the top than the unslatted config. this is a way of holding back the Stall, surely, but Stall isn't the consideration, foremost, lift is. A wider chord and increased camber airfoil produces more lift at any speed than the standard wing. Once slow speed lift augmentation is accomplished, they are retracted. The ribs that extend the device do just that, they are not there to allow airflow to change its mind and swap sides after passing the leading edge. At 100 knots, how much airflow will change direction by nearly 90 degrees to passively "Blow" (supercharge) the top surface?

Wiki indeed.

Will

I suppose they were also having an advantage from still being in the ground effect. at 32.8 feet.:eek:

The 747-400 does not have Slats (whatever Wiki says). It has a mixture of Kreugar Flaps (inboard) and Variable Camber Leading Edge Flaps.

Dave

All very hard to understand.

I guess Boeing will review the DFDR and various reports they have, may be they will remove the L/E/H/L/D from the 747/44 to save weight, but a I have feeling may be they won't.

To knock the same old nail, well done to all involved, lets hope we don't have a repete act with the 747/44 L/E.

Still baffled
 

I've read this thread again from start to finish and I still don't understand exactly what the crew did and why. Given that the amber rev unlocked lights were on for 2 & 3, and given that that the stick shaker deployed before they realized that the L/E devices were retracting, did the crew advance thrust on all 4 engines (the right course of action in this case) or just 1 & 4 (which you might say was a more intuitive action if the inboard reversers were in fact starting to unlock).

Or did they just say "well, if both inboard reversers are unlocking, the aircraft isnt going anywhere anyway so we've nothing to lose by assuming it's two false indications and taking it to the max on all four".

In fact it's more than that, because without knowledge of the L/E slat retraction surely the intuitive assumption would be that the activation of the stick shaker was due to a degradation of performance caused by the inboard reversers starting to unlock?

The thing that I cant understand is that they appear, on the basis of the admittedly shaky info on this thread, to have done the right thing based on illogic...

Much respect, whatever the reason.

Pinkman

The simplest technique is always to put all thrust levers to Full thrust - when things have calmed down you can decide where the problem lies. In the heat of the moment being selective may equal being wrong.

Pinkman,

in summary:

the handling pilot flew the jet by feel into a dark hole at night with the jet at aroun 10'-20´ for what must have seemed like forever. 10deg pitch its hits the ground, 11.5deg it stalls. thank god he had the talent and experience to operate so far beyond the scope of our scenario driven training.

the skipper faced with no way of knowing what was happening on the wing made 2 decisions which it would appear, in tandem with the outstanding efforts of his co, got everything moving back into the right way.

Im not spock but I think it´s harsh to imply it was illogic thinking that saved the day here. what saved the day was a great deal of talent backed by an ability to make decisions under huge levels of stresss and uncertainty.

Im biased. I know both individuals and will consider it my privilage to buy them both a bottle of whatever they like when next in the bar. they saved a jet full of lives and possibly, but less importantly, my company and therfore my job.

Bravo gentleman.

In answer to Dave's reply to reprogramming the FCUs to not have the autoflap function at flaps 25 and 30.

I would guess it would be possible to reprogram the FCUs so they could work in the sense you describe but without knowing the internal workings of the FCU I wouldn't like to speculate on what could be possible.

I have looked at the wiring diagrams for the T/R and Flap Systems and it is fairly simple in that when either T/R1+4 or 2+3 are detected unstowed(not deployed) and aircraft on the ground the Group A flaps retract. The input to the FCU from the T/R position system is a ground that is switched by a relay so I would imagine that Boeing would look at interlock circuit involving relays with some input from another source such as the throttle lever as previously suggested.

Hope this is of interest.

Slat function carried out on ground which involved T/R function not enough air because of sea level of jnb.T/r did not go back all the way but looked alright on ground.This did not show up until T/o roll.Expect to see changes to MM after Slat and T/R functions by Boeing.

Heavy Heavy
 

You're reading harshness where none was intended. What I was trying to understand is what led them to make the choices that they did when so many scenarios presented themselves in a few seconds. Thats all. If you PM me your address I will happily send you the cost of a second round in the pub for your colleagues. When I lived in RSA I flew that service often, either directly or via a Comair feeder when the CPT-LHR service was full. As I said in my post...much respect.

[Edit] Now we begin to get answers: SkyBoeingEngineer indicates that there was mtce carried out. I assume that would have been briefed in the handover. So that more or less answers my question about why they did what they did. The Rev Unlocked lights didn't 'just come on'. They came on during the t/o roll following prior operation of the T/R on the ground by mtce. The crew made the choices they did, not illogically, but with the knowledge that it was likely to be spurious and that it would have caused the inboard L/E devices to retract. Thats all I wanted to know.

Air Ground
 

I did not take the time to read trough the whole story.

I seems to me that the air/ground logic must be in ground mode for the LE Flaps to retract.

How can this happen in the Air?

Bitburger

It didn't happen in the air. It happened on the ground after V1 but before Vr. It pays to go trough the whole story.

"The ribs that extend the device do just that, they are not there to allow airflow to change its mind and swap sides after passing the leading edge. At 100 knots, how much airflow will change direction by nearly 90 degrees to passively "Blow" (supercharge) the top surface?

Wiki indeed."

Will Fraser, surely that is exactly why it happens....the higher pressure underneath creates the lift and if there is a hole anywhere then the higher pressure will bleed to the lower, regardless of speed of Aircraft or airflow.

JSP

Will, I use Wiki a lot, but not for basic aerodynamics. 5 years studying for an Aero Eng Degree and practicing a wee bit afterwards means I don't need to...

The predominant effect of le devices is to extend the lift curve slope,
The predominant effect of flaps is to give a Delta Cl increment (with varying degrees of Delea Cd, becoming very significant at full flap positions)

I was indeed talking slotted le devices, but even if not slotted on the 747, the le camber has a similar effect, the predominant one (Wiki has it right) to extend lift curve slope (to higher alphas), since without the le camber, flow breakdown will occur earlier - but yes, an extension and camber will give a delta Cl increment as well.
So in actual fact for the 747 we're both right :)

As pointed out above, the pilot flying was doing a great job right on the edge of a cliff, between the devil and the dep blue sea, having a very narrow margin of operational alpha until he could dump some drag and pickup a few knots here and a few there...

Another Sully, making simple, basic, and most importantly quick decisions! He won't get to retire and write a book though... :rolleyes:

"he 747-400 does not have Slats (whatever Wiki says). It has a mixture of Kreugar Flaps (inboard) and Variable Camber Leading Edge Flaps."

The variable camber flaps on the 747-400 do have an air gap between the flap and the wing, so probably exhibit slat-like behaviour.

Rollers on the 400 have a poorly designed proximity switch which has a long history, the fix by some airlines has been to check the rigging more frequently to prevent unwanted reverser messages, air load and/or thrust loads can cause a slight shift of the reverser as you could expect as components wear which sets off the proximity switch. Locking out the reverser doesn't fix the problem always either as the wear and or rigging won't be fixed by a locked out reverser, so you lock it because of the faulty message taxi out set thrust get the same message. Delay flight to re rig reverser? You can't change the reverser either as it requires the entire engine to be changed.

Experienced RR guys have probably seen all this before so know or try to do what they can to prevent unwanted reverser messages.

Was any work carried out on any of the reversers while in JNB?

The 'air gap' will also be a feature of the new 747-8 I/B Kreuger flap it's being redesigned for this purpose.

A tribute to basic flying skills indeed and another weight to chuck into the on-going debate about the on-going erosion of those skills.

For my benefit (assuming I have this right), can anyone give me an idea of the time scale for all this? I. E. typical V1/Vr in Jo, how long retraction would take on the faulty signal and how long again to re-extend on the a/g switching? Do the L/Es have to complete retraction before they will re-extend or can they be instantly 'reversed'?

7 seconds rings a bell for some reason and they would not need to complete a full cycle, should just stop and then change direction.

NB NO 747 experience...

Whilst I resisted calls for 'Boeings head' on the Schipol Radalt accident, and given that as usual we are all working here on 'hearsay', I would question why B did not think about this 'failure' and its consequences above V1. Assuming it happened above V1 as stated, it left the crew with no real options but to continue with a crash extremely likely. The ensuing rotation must have been eye-watering! The call for inhibition of the LED retraction with more than xx power set is very strong.

If this failure should happen below V1 but at high speed............ I guess the T/off emergency briefs will be changing until mod action is in place.

A think that you will find most 747-400 drivers will now call stop for a thrust reverser amber, with or without any other cue (swing etc).

Ex JNB at about 350 tonnes TOW, the V2 will be about 174kts with V1 about 155 and Vr high 160's at a guess, take off roll about 65 seconds and 4000 metres.

If I had an unlocked warning on the T/R(s) that maintenance had been working on, I would not assume it was spurious!!!

tyro

I believe that the inbound crew had reported a failure of the autospeedbrake on landing. The outbound crew would probably have been faced with an engineering item saying that some 'tests as per Maintenance Manual x.y.z carried out, and system satisfactory.'

They would not know what specifically had been carried / have reason to suspect that the reversers had even been part of that procedure and would have taken it as read that the engineers had done everything as per the book.

You may well be right, TopBunk, but I was responding to a statement by Pinkman about the thought processes of a crew who had been fully briefed about maintenence actions, which then transpired to have not been correctly done...

Rectification of which presumably would not involve the LED and T/R....

TopBunk.......... correct!
TyroPicard............ also correct!

Pinkman - there'd have been no handover after the maintenance. The aircraft lands in the morning and leaves in the evening. Probably wasn't even the same engineer on duty when the outbound crew accepted the aircraft.

I think they might have scribbled a little note in the log.

Didn't work the 747, does reverse thrust pop the speedbrake lever up?

Please tell me that you're pulling my leg. Surely when a new crew accepts an aircraft they get briefed on any aircraft performance issues on the inbound leg, any maintenance actions, MEL items etc? It shouldn't matter whether the aircraft has been on the ground two hours or twenty hours or how many shift changes there have been in between.

I cannot believe the crew did not know about any maintenance, whether or not it involved the reversers and whether or not the reversers were actually deployed on the ground per the earlier post. This goes back to my earlier question about whether all or just 1 & 4 engines were firewalled. Why would you firewall the other two engines if you seriously believed the reversers actually had deployed?

<A think that you will find most 747-400 drivers will now call stop for a thrust reverser amber, with or without any other cue (swing etc).>

Not after V1 I hope!!


and yes the crew would have known of any engineering input as soon as they reached the aircraft and examined the tech log.

The tech log will tell you what the speedbrake defect was on landing and whether or not the engineer cleared that defect. If they want to know the procedure used to fix the defect they can look in the MEL. If Pinkman thinks that there'll be an engineer waiting at the aircraft waiting to personally brief the flight crew on what was done in detail then he'll be disappointed.

The maint manual will tell how to invest/test/fix. (FIM)
.
The MEL may tell you a lock out proc or similar.
.
Trying to read between the lines here, systems may have been tested using APU or ground cart air, duct press may have been unstable due demand of Rev's and demand hyd pumps(ADP's) due spoiler ops.

The above may lead to Rev's being stowed and locked, but just not at the max closed/near position(prox) a prev post by SMOC is about right, Hi power and a few bumps on the T/O could be just enough for prox to be far.

Remember, in normal operations, 4 engines running = good duct px for Revs and demand pumps(ADP's), plus 4 EDP's giving loads of hyds for spoilers.
.
The following link is a good slide show..
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Fc744 Flightcontrol
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I guess I'm disappointed
 

I guess I'm disappointed. In my industry (fuel refinining) where equipment fails at any time of the day/night, is fixed, things catch fire and go bang causing the same kind of loss of life as your average aircraft disaster we personally brief EVERY shift, EVERY handover, have tech logs, defect logs, etc. Its very formal.

Desk Jockey: Yes engines 2 and 4 in rev will auto deploy speedbrakes - Other conditions also need to be met i.e a/c in ground mode. (To overcome the lever lock solenoid)

Isn't that something to do with the landing gear lever? :}

Not according to the schematic!

Yes, there is also a "lever lock solenoid" on the speedbrake schematic.

However, this relates to the Flight Detent. It has nothing to do with Autospeedbrake ops ;)

CHeerS
NSEU

It always amuses me to see everyone picking over the bones of these incidents in great detail, being wise after the event.
I thought that's what official investigations are for?


Having heard what actually happened from those VERY close to the event, I assure you it relies on pure instinct and all those hours of flying you've managed to accumulate over the years. So when the details are finally published, it would be nice to see all self appointed experts return to this thread and give the crew all the credit they will undoubtedly be getting.

And perhaps put themselves in the position of those who found themselves in a situation way outside anything ever they've ever experienced or been trained for.

Nevermind

If thats the way you view PPrune, then the forum isn't for you. The forum is for people - nominally pilots - that view what they do as more than a job, have impatient, inquiring, minds, and are passionate about continually learning from mistakes, incidents, and near misses to improve their own performance. It includes not just pilots but some of the finest technical experts in other aviation related areas including ATC, engineering and maintenance, airframes, aerodynamics, runways, fuels, aviation medicine, aviation law, and much more.

The accessibility of the forum means that you get a proportion of posts from idiots, poseurs, and tosseurs, but the moderators weed much of it out. I don't see anyone on this thread being wise after the event. I don't see anyone on this thread criticising the crew or setting themselves up as self appointed experts.

What I DO see is lavish praise and huge amounts of respect for that crew as people on this forum try to understand what happened and why.

Read post 97 on this thread from 4PWs and tell me how you get to where you are from there...