Frost
 

I agree fully with Chris. This is based on a survey of about 50 photographs of landing B777s showing the wing undersides. I can find only one picture possibly suggesting wing surface frost in the tank area (ANA-Star Alliance plane).
I would imagine the airflow in most cases prevents frost (or ice) to form until the plane has landed and slows down. The wing underside is also a high pressure area, meaning that moisture is less likely to condensate on that part of the wing than on a low-pressure area.

That said, most of the pictures are taken in conditions of less humidity than the weather BA38 had.

But if it's frost that is visible on the BA38 picture, it might be a fairly unique occurrence?

Here are some pictures:
http://www.!!!!!!!!!!!!!!/photo/Korea...-ER/1341078/L/
http://www.!!!!!!!!!!!!!!/photo/Briti...-ER/1339905/L/
http://www.!!!!!!!!!!!!!!/photo/Air-C...-LR/1342818/L/
http://www.!!!!!!!!!!!!!!/photo/Conti...-ER/1339702/L/
http://www.!!!!!!!!!!!!!!/photo/Jet-A...-ER/1338232/L/
http://www.!!!!!!!!!!!!!!/photo/Star-...-ER/1336739/L/
http://www.!!!!!!!!!!!!!!/photo/Briti...-ER/1333455/L/
http://www.!!!!!!!!!!!!!!/photo/Briti...-ER/1326063/L/ G-YMMM
http://www.!!!!!!!!!!!!!!/photo/Korea...-ER/1325100/L/
http://www.!!!!!!!!!!!!!!/photo/Korea...-ER/1321846/L/

EDIT: Based on some more searching, frost on the underside is not totally uncommon but still fairly rare. A search turned up a total of 3 pictures with visible frost under the tanks.

http://www.!!!!!!!!!!!!!!/photo/Finna...-11/0991454/L/
http://www.!!!!!!!!!!!!!!/photo/Virgi...443/0764483/L/
http://www.!!!!!!!!!!!!!!/photo/Gulf-...101/0701662/L/

Frost and positive TAT
 

To Chris Scott and snowfalcon2:

I've checked A.net pictures as well today and came across almost the same pictures snowfalcon2 posted. I agree with you that actual fuel quantity is probably somewhat more than the frosted area for the reasons you explained. Making it only more likely there was sufficient fuel in the tanks before the moment of impact.

For it being a rare condition to observe frost on the lower wing surface, that may be when searching photographs for examples. But since I've performed countless post flight inspections and also participate in de-icing activities as a supervisor in winter seasons I come across frosted lower wing surfaces quite regularly if the weather conditions are right for it. Indeed the fuel level in the tanks usually exceeds the frosted area somewhat which can be observed by a wet thawed area bordering the frost at + deg. C conditions. This condition cannot be determined from the G-YMMM subject photograph but was probably present.

Therefore, I do believe the fuel quantity in G-YMMM's case was slightly more than the frosted area in the picture and will take it into account when making any calculations. However, I'm still convinced that the center wing tank was empty when observing the clear outline of frost starting at the rib, separating wing tank(s) from center wing tank. Also because of the absence of frost near the wing root.

Green-dot

Yes, more powerful hardware is available now - but do you know *why* the decision was made to use older hardware, and indeed why previous generation hardware continues to be used in safety-critical situations?

In the home and business sectors of computing, the onus is on bang for buck - no-one particularly cares if a fast processor crashes once in a while if the worst that can happen is losing a report that's due in tomorrow. In safety-critical systems the focus is on predictability - knowing that barring a catastrophic hardware failure a certain input will *always* produce a given output.

In the case of the Airbus system, the 80186 was a 1982 update of technology that was released in 1977, and had been developed for several years prior to that. Which means that it was in effect 6 years old by the time the A320 was delivered (26 years old now), based on technology that was 5 years older than that (31 years old now). Then as now, 6 years is a long time in microprocessor development.

Processors of that vintage were very simple technology by today's standards - but that's what makes them useful in real-time, safety-critical systems. As a Software Engineering graduate you'll remember your first Hardware Architecture lesson and the diagram you were shown, illustrating the program counter, registers and arithmetic/logic unit. '70s and early '80s era processors were slightly more complex but still hewed to that basic design. Today's modern processors are nothing like that - they are essentially a CISC translation unit which takes the x86 instructions and translates them into a format that a highly-complex RISC back-end then uses to do the grunt work. Such a design is wonderful for today's desktops, workstations and servers but their complexity makes it a challenge to answer the safety-critical question of predictability with any conviction.

Hence the A330/340 was introduced 4 years after the A320, but still used the 80186 in the SEC. The Space Shuttle continues to use heat and radiation-hardened variants of the Motorola 68000, a design of similar vintage to the original 8086 (but logically structured more in line with the PDP-11 computers used in development in the 1970s). The latest Honeywell FMS uses an AMD design that's 20 years old now.

Anyways, that's how I understand it - I'm sure the Prof will correct me if I've made any glaring mistakes, seeing as my knowledge was only current when I graduated Uni 7 years ago.

Apologies to the mods if this post is too far off-topic.

Dozy, not off thread, wonderfully ON thread to straighten some of the wonky lines that people have been shooting in here.

I am sorry that PBL cannot continue (for whatever reason) and, whilst remaining fascinated by this mystery, I think that I shall wait the results that RTFM has kindly calculate at 25.6 months. My thanks to RTFM for that, it confirms what I have said so often.

Many can now draw a sigh of relief as I leave this thread to it's natural end ...

Dozy: slight correction - Shuttle flight computers are actually made by IBM and the architecture is an update of the S/360 developed in 1960s (and is still in use today albeit much enhanced on the IBM mainframes).
The actual processors had a well tried pedigree as an avionics processor in such aircraft as the B-52 (obviously the later variants).

I believe the main idea is:
there was actually cold stuff (hopefully fuel) in these main tanks, and obviously enough for another 2 miles.

But still, I’ll be interested if Green-dot is able to produce an estimate.

I would not bet on any figure, but to me, the area looks pretty tiny, at least more tiny that the one from ANA when blue sky (and Metar confirms temp / dew point) was not optimal for that frost formation. To have access to that ANA remaining fuel could provide some direction of thinking …

http://i45.servimg.com/u/f45/11/75/17/84/ana_0210.gif


Regarding BA038, humidity was effectively more important with that broken at 1000 ft confirmed by a 2 deg dew point spread on surface.
I do agree that TAT has an influence, but not that much in this case when you consider this remark:
“clear outline of frost starting at the rib, separating wing tank(s) from center wing tank”
Nevertheless I do consider the limited cold fuel influence on the outboard as volume is lesser, but I still find the outline quite marked.

Just one more thought:
Considering the huge size of the CWT close to 100000 liters (and also the architecture, as I understand it the tank is not in direct contact with the fairing skin ?) I’m not sure even 10000 liters would be made visible by any frost on the left or right side of that tank, as that volume would be exclusively in the lower part, just in the center of that center tank … ?

CONFiture

The wing fuel tank on the B777 goes a long way inboard of the strut.

I can't comment on how often frost is seem while aircraft are landing, but I do meet B777 every day on the ramp at ARN. On arrival on the ramp there is nearly always frost under the wings like on the picture above. The area under the wings inboard of the engine normally shows a clear line where the wing tank ends. Frost under the wings on long haul aircraft is there on arrival at the ramp about 90pc of the year. The air must be very dry for it not to form.

LurkerBelow:
Aye, you're probably right. I think the 68k was used in the engine control system rather than avionics.

A-320 is a totally different kettle of fish but, if I DONT see under surface wing frost on a turnround, I think something is wrong!!

Its a pure case of cold metal descending into warm air and picking up the moisture, its not an issue at all.

Tank frost margins
 

Just how closely the under-wing frost defines the ‘wet’ part of a wing tank is a matter for some conjecture. I don’t disagree with anything that’s been said; nor amend my suggestions above.

Swedish Steve is our most experienced B777 witness on the ramp, and has stated that the inboard edge of the tank is clearly discernable. This is, of course, where the fuel is deepest; and the massive rib that forms the end of the tank has itself been refrigerated by the fuel for many hours. At the opposite end of the tank (the end we are considering), the shallow fuel is lapping the shore, so to speak; and not contained by a rib in the presumed fuel state.

CONF iture has reminded us of the centre-section (belly) fairing, which on most types is deepest at the forward end. My dial-up connection discourages me from downloading snowfalcon2’s excellent photos of the B777. But other types have enough depth to accommodate the air-con packs at the front. Further aft, the forward base of the centre tank is also well within the fairing. For example, tank-pump canister-plates are only accessible via an access panel on the fairing; likewise the magnetic fuel-level-indicator sticks for the centre tank.

snowfalcon2, could you tell us the extent of the B777’s belly fairing?

Subject to the above, I don’t think absence of frost on the belly fairing would tell us anything about centre-tank contents. As for the wing tank, see my post above. To paraphrase what I said: presence of frost indicates presence of fuel; conversely, absence of frost does not necessarily define precisely where the fuel is absent.

http://www.!!!!!!!!!!!!!!/uf/536904336/phpElb51J.jpg

Took this this afternoon. A B777-200ER of Malaysia airlines just parked on the ramp at ARN after an 11 hour flight. This frost cover on the lower wing is typical. Total fuel on board 9700kgs.

Oh dear picture did't work. Will try again later.
Thats better.

Hi,
 

I'm not sure if I understand the question 100%. I believe there are several posters here with a much better knowledge of the B777 tank construction than myself.

What I can add is the regulatory requirement. FAR 25.963 "Fuel tanks: General" states that:
To me, this means that the centre tank is inside the structure and thus frost formation on the outside of the belly due to cold fuel is highly unlikely. Maybe our Swedish contributor can confirm that.


Agree, see above. However, the centre tank does reach into the wings, as this incident report shows, so in theory frost could form on the wing underside portion of the centre tank if it contains fuel.

It is interesting that while underwing frost is commonplace on parked airplanes, judging from the photos it's quite rare to form while the plane is airborne, as it did on BA38. How rare, is an interesting question.

Very good Steve !
As frost shape is quite similar to what we saw under MMM, I think it does validate the "indicated" 10500 kg from AAIB report.
Thanks

A bit off thread, but...

... jolly nice to see an MH arrival with a bit of spare fuel on board... :)

If you look at my picture, the centre tank starts where the frost ends, and goes right across the aircraft. The wing/body fairing covers the centre part of it completely.

http://img61.imageshack.us/img61/620...anksvh4.th.jpg
http://img57.imageshack.us/img57/574...nks2dm2.th.jpg

G-YMMM approx. fuel remaining . . . .
 

Quoting CONF iture:

And Swedish Steve:

Very similar to the frost area under MMM, see picture and drawings below:
http://pickyperkins.home.infionline.net/photo.jpg



http://pickyperkins.home.infionline.net/front.jpg


http://pickyperkins.home.infionline.net/tanks.jpg


With special thanks to a fellow PPRuNe-er for helping me get wiser on how to post images here.

Checked another B777-200ER here at AMS during a post flight insp. which had approx. the same area of frost under the wing.

Regards,
Green-dot

So in layman's terms we can put the "poor fuel management" theory to bed with the EMI nonsense - is that the case?

Oh, and another thing I forgot from my earlier post - older processor designs didn't use as much power and didn't require large fans to keep the temperature under control - in engineering terms fewer parts = fewer things to go wrong.

I am very interested to know all the differences between advancing the B777 thrust levers vs advancing them to maximum.

I suspect we could ever since one of the two AAIB reports commented that indicated fuel was more than adequate.

'FAT' with Fuel...
 

Congratulations to our two ramp men - Green-dot and Swedish Steve - and CONF iture, for finally kicking the OUTAGAS theory into touch. [If the crew or anyone connected with the AAIB ever reads this stuff, no doubt they will have cracked a wry smile.]

Dozy Wanabee,

It's easy to dismiss other people's areas of enquiry as "nonsense". But in the absence of alternatives, was this accident purely an act of God? How about reminding us all of your more sensible theory?

This is an accident with very rare circumstances, likely never encountered before. In the order of 10 to minus 9 power: extremely improbable but with catastrophic consequences.

Chances are that the combinations making this happen are conditions that have never made it to the list of required DFDR parameters.

My guess is that if they find the cause to be a unique set of circumstances, the list of recorded parameters will possibly once again be extended.

As an example, such was the case when the B737 rudder PCU servo-valve had been identified as the cause of several accidents.

In case of the 737 rudder problem the conception was also that all swans were white, until presence of a black swan (the PCU) was identified.


Green-dot

Do you mean something like this?

I wouldn't take silence on the part of the AAIB/Boeing/RR/BA to mean that investigative work has slowed down; just that there is nothing more to report that impacts current operations. I'm sure if they turn up something safety critical, there will be an AD or special bulletin out PDQ.

Maybe the mods are just tired of the same old speculation? This second hand account actually ties in very well with the current AAIB report, given that the person relating it wasn't a pilot so could easily confuse loss of all engine power with loss of control of the engines... Who knows?

That would be the one where the retrofitted rudder controls (to fix the problem) included duff control rods that could also lead to uncommanded hardover ? :uhoh:

I think the investigation in that case included a lot of serious test rig kit with rudder assemblies in cold boxes etc. - for G-YMMM you might want most of a wing (+engine) in a cold box. Yikes.

Comet hulls in swimming pools also come to mind.

I wonder if there will be that level of resource put into this incident at this point - at some point, I guess, they decide not to spend any more on investigating what is clearly a very very rare event.

That B737 rudder issue, and the Comet, weren't investigated in the level of detail required until after multiple hull losses - I wonder if we'll ever get the answer on G-YMMM... :hmm:

The presence of fuel in the tank does not completely rule out mismanaged fuel. What happens between the tank and the engine, and if selectable might not be apparent to the investigators, i.e. not on the FDR.
There is evidence (or inference) that with the fuel metering valve open there was insufficient fuel flow to accelerate the engines; thus whatever is in between, could be mismanaged either manually, automatically, by design, or unintentionally.

This is what ruins PPRuNe and threads such as this. Anoraks and their ridiculous theories on subjects they know nothing about. I'm glad those posts were removed. 'Sunspots caused the crash' my @rse.

If you want to spout rubbish do it in Jet Blast or, better still, on another site and leave the grown up subjects to those of us with a vested interest.

Back on topic now please.

The reports seem to indicate that this was the case.

I've had a ponder about how you could deliberately restrict (not shut off) the fuel flow to the engines and I can't really think of a reliable way of accomplishing this without some rather noticeable secondary effects (!). The main tank pumps can be turned off without affecting the fuel flow (at sea level, that is) so you'd have to put both fuel control switches to cutoff or pull the fire handles, then pull the CBs for the spar valves to try and freeze them in a slightly open position, then quickly re-instate the FC/FH... I don't know what the transit times are, so it might not even be possible. At that point the FBW, autopilot, electrics, etc. would have all gone for a ball of chalk, not to mention the RAT deploying. I think we can put this scenario down as "unlikely", at the very least!

Can someone please close this thread?
It looks like it is going into a dead end street (if it ever ends?) where they will give you a free pukie bag to get rid off all the theories and thesis gathered by mostly "experienced" and qualified researchers along the way.I think CAA will have the final word on it after all,right?
The only other thing I can match with this is a thread started by a BA union rep when it comes down to strike or something similar...100.000 views and all that, almost like a soap opera or a set at Beverly hills 90210 on the end.
Boring and mundane or just superficial who knows.

Quoting safetypee:

Or uncommanded . . . .


Quoting Flintstone:

Sadly, what is worse, are biassed threads . . .

Biassed:

1. A statistical sampling or testing error caused by systematically favoring some outcomes over others.

2. To influence in a particular, typically unfair direction; prejudice.

Time for me to study a bit more about some specific issues in the T7 AMM, WDM, SSM and FIM regarding ATA 28-22-15. Understanding you are a professional, i will skip the details . . . . .


Just for the record, this post originally contained 3 replies to 3 different posters. Somehow 1 reply was removed/deleted minutes after i submitted this post on the 17th of april.


Regards,
Green-dot

I wish this thread could be locked and removed. In an effort to correct the record regarding the Comet, if my memory serves me correctly, it was a design defect, not a construction defect, that caused the in flight break-up. To whit, "square" windows in a pressurised hull, leading to stress concentrations at the window corners. It had nothing to do with the redox bonding process.

Quote from Flintstone:
If you want to spout rubbish do it in Jet Blast or, better still, on another site and leave the grown up subjects to those of us with a vested interest.
Back on topic now please
[Unquote]

Quite. And your theory is...?


Skydrol Leak,

The most ludicrous posts on this thread are those asserting which topics are kosher; and which taboo. Thank you for your gratuitous rant. The solution is simply this: if you object to informed professionals (and even me, given the chance ;)) discussing the merits and weaknesses of hypotheses that you find counterintuitive, or unpalatable; don’t click on this thread, it’s not obligatory. And beware of Skydrol; it can blur vision.

Chris

Better still, have the mods delete the rubbish and have something approximating a reasoned and informed thread.

Oh look, that's already happening.

Better ideas, anyone?
 

“… also for turning up something that hasn’t been properly understood before …”

Like the Lightning gear collapse during landing attributed to a structural vibration (resonant frequency) which momentarily moved the mechanical portion of the electo-mechanical valve? This, IIRC, involved a very few events on one variant type, but was a rarity without logical explanation.

Are there any interesting vibrations, system selections, or characteristics which could contribute to such a theory during an approach in a 777?
If so then presumably with structural considerations, there might be an enormous combination of weight, cg, configuration, speed, turbulence, control input, intersystem activity, etc that might account for the apparent rarity of this event.

Mystified
 

I don't spend much time worrying about it, but note how baffling it is that there are those who post how irritated they are by other's posts. If one is annoyed, and insists on shutting a thread or that other's simply shut up, wouldn't it be easier for them to move along? Why would one wish to be irritated by other people? Seems somewhat immature.

Which brings me to this moment. I do not believe Websites have ANY obligation to allow full and free access to those they wish to exclude. This isn't a "Free Speech" environment; that would be the Public Square, which this venue is NOT. This is Private Property, and as such requires deference to, and respect for, the OWNER(S). I have believed that since the beginning of the Ether.

BA38. In 1988 (roughly) our company, with its progenitor, Boeing Aircraft, was looking at ETOPS. There were essentially two camps, as there are re: mandatory 60 year old retirement. Two crew Twin engine A/C were an assault on all who held dear the concept of "Four's enough, but not too many". Loss of the Flight Engineer was difficult as well. Many were very sceptical of two engines more than gliding distance from an Aerodrome.
As the BA38 issue unfolds, I continue to fully believe in ETOPS, though initially my faith was shaken. I continue to be confident because I think the incident was unrelated to ETOPS. A combination of reading, sifting through admittedly sparse Data, and Intuition tells me that. I am fascinated by the posts here, by those far smarter and more experienced than I, and I think to squelch vigorous and respectful debate would be a great Loss. As I have said, this post is now the property of the owner of this website, to do with or not whatever he/they may wish.

AFM

Against stupidity, even the Gods struggle in vain.

This is only my second post, so forgive me if I appear to go over old ground.

I fly for fun, but my real business is power.

I know elsewhere, that wax has been targeted as the culprit, and in my view, this is partially correct.

When wax forms in fuel, it is also the fraction of the fuel with the most heat, that has been effectively removed, and the heat left in the remaining liquid will be at a lower heat value, and this could be further aggravated if the remaining fuel has in fact separated into its other fractions, with the worst fuel( lowest amaount of energy) being at the bottom of the tank.

The result, in my viiew is that the FADEC worked fine, but the amount of fuel pumped into the engine lacked the required energy (kJ) to meet the power demanded.

Just my 2 cents worth from a dreaded PP.
Cheers

Wing and engine in a cold box
 

Firelight and Infrequentflyer789

Yes, yikes! I don't think a "cold box" of the necessary size would be too difficult to find. Expensive yes; there are some pretty large reefer warehouses around but renting one out for a few months could put a considerable dent in the distribution of beef or frozen veg. Getting the temperature down to minus 50C would be a challenge (normal working temperature being minus 18-20C) and intake/exhaust another, assuming the engine would have to be working.

If the AAIB were to go the route of testing temperatures it would probably be more expedient to rig up a prefab coldstore around an existing airframe.

oh, and Brian... JS Mills?

...... and Von Hayek.

AFM:

The reason the EMC zealots get short shrift is that as a rule, they violate the precept that 99% of other proposers of pet-theories manage to follow:

No matter how improbable your theory, please walk through it from cause to effect. Those opining on fuel waxing, FADEC failure, inner engine icing, pilot error, partial spar valve failure, etc all at least provide the courtesy of a scenario and some sort of support chain.

IMHO, only the proponents of mystical EMC feel that a bit of arm waving, appeal to the vagaries of past unexplained accidents, and exasperated frustration that their explanation is not just ratified as-is, can somehow suffice as support for their otherwise unsupportable stance.

This comes to mind:

http://i29.tinypic.com/k33z9c.jpg

That is simply not how scientific inquiry and accident investigation in particular is to be approached. Einstein said: "Keep an open mind. But not so open your brain falls out."

:E

System characteristics.
 

Quoting safetypee:

Taking the AAIB reports published into consideration, (perhaps the investigation has progressed beyond what has been published sofar) if no evidence of an anomaly has been found:

Approaching the issue from another angle, i would go for a combination of system selections (including interaction or possible interference with other systems) and characteristics.

A question that comes to mind would then be: which (sub) system components could (due to a yet undefined fault) migrate from commanded position without generating a fault indication to the flight crew but result in reduced fuel flow and cause engine rollback?

A question related to the one above is, why was the APU door open during approach if there was no mention in the AAIB reports of an electrical power failure? Isn't the APU normally an after landing checklist item?


Green-dot