How Did MH370’s Flaperon Come Off?

In my last post, I reviewed Malaysia’s analysis of the MH370 debris its investigators have gathered. Not included in that study was the flaperon found on Réunion, as it is being held by the French. So today I’d like to look at what the damage patterns seen on the flaperon suggest about the crash, based on the work done by IG member Tom Kenyon and by a reader of this blog, @HB.

On February 3 of this year, Kenyon released an updated version of his report “MH370 Flaperon Failure Analysis” in which he gives an overview of the flaperon’s structure and how it was damaged. He notes that of the six main structural attachment points of the aircraft, the two biggest and most significant are the flaperon hinges (pictured above). They snapped in the middle:

The lesser attachment points failed in a similar way. That is to say, they did not rip away the flaperon structure to which they were attached.

Kenyon observes:

The location of the failure points of Flaperon hinges is consistent with a large singular lateral force or repetitive lateral (or torsional) movement of the hinges in the inboard/outboard direction. If Flaperon was separated from the Flaperon hinge with forces in forward/aft direction or by applying forces to the Flaperon in the extreme rotated up/down direction (beyond structural stops) then deformation of the Flaperon structure due to such forces would be evident. Significant and permanent deformation of the Flaperon structure does not appear to be present in photographs of the Flaperon.

Recall that two scenarios have been proposed for the flaperon coming off 9M-MRO: either the plane hit the water, or it came off as the result of flutter in a high-speed dive. Neither event could reasonably be expect to produce a primarily lateral (that is side-to-side) force on the flaperon of the kind Kenyon describes.

To raise the level of perplexity, Kenyon points out in other crashes involving 777s, failures didn’t occur at the hinges; rather, the hinges remained intact and the material to which they were attached broke. That is to say, hinges are stronger than the flaperon proper. Here’s an example from MH17:

Kenyon concludes that:

No significant evidence of secondary structural damage excludes a massive trailing edge strike and leads the author to conclude that the Flaperon separated from MH370 while in the air and did not separate from the wing due to striking water or land.

In other words, since the damage isn’t consistent with a crash into the sea, we can deduce that flaperon must have come off in the air. The only conceivable cause would be high-speed flutter. However, on closer inspection the evidence seems to rule out flutter, as well.

The reader who goes by the handle @HB is an expert in quantitative risk assessment in the transportation industry and has extensive experience with composite materials. In a comment to the last post, he observed:

For the flaperon… the lift/drag load is normally passed on the honeycomb panel over the exposed surface area then the primary stucture of the component (the aluminum frame of the flaperon) then the hinges then the primary aluminum stucture of the wing.

In a nut shell, those panels are not designed to sustain any in-plane loads either compressive or tensile. They are just designed to resist bending due to uniform lift load on the surface (top FRP layer in tension and bottom FRP layer in compression, the honeycomb is basically maintaining the distance between the layers without much strength).Those panels can arguably take a little bit of shear load due to drag forces on the top skin (top and bottom forces in opposite direction) but not much due to limits in the honeycomb strength.

The second thing to consider are the GRP properties. The GRP is very tough in tensile mode, much stronger than Steel. In compression mode, it buckles easily and only the honeycomb is preventing this. This is by far the weakest failure mode. If it fails, you will see fibres pulled out link strings on a rope failing under tension. For the skin under compression, you will see sign of compression on the honeycomb but the fibres will have to be pulled out as well. Also, a perfect manufacturing does not exist, there are always delamination (small bonding defects) between the honeycomb and the GRP skin to weaken further the compressive strength.

The hinges are usually much stronger as all the load is passing through them (analogy door hinges).

So you could imagine, if there is a large impact the hinges are expected to fail last. The part of the skin that will buckle is expected to fail first.

@HB here is agreeing with Kenyon: it is baffling that the flaperon came off the plane due to failure within the hinges. But @HB goes further, arguing that this type of damage is inconsistent with flutter:

I would tend to agree that the hinges have been subject to cyclic fatigue… the hinges appear to have been subject to cyclic lateral forces which are not expected in any accidental circumstances (take door hinges, for instance, and imagine the hinge fail after 50 times someone is trying to burst through – you can try at home but it is very unlikely to happen). This of course requires a closer look by experts to double confirm. I cannot think myself of any possible lateral force on this part in the first place but a lateral force that will fail the hinges and not the skin which is weaker is very hard to explain. Try with a wooden door and tell me if you manage.

In a followup comment, @HB observes that even under very strong oscillation the flaperon should not be expected to disintegrate. “If hydraulic power is on, fluttering is unlikely to cause any disintegration. If off, fluttering forces are up and down and the hinges are free to move. Lateral forces, I think, would be small in comparison with the vertical forces and not be strong enough to cause fatigue on the hinges.”

Kenyon concludes his report with a list of six questions and issues generated from his analysis. While all are worthwhile, one stands out to me as particularly urgent:

• Why are the official investigators silent on releasing preliminary reports on their Flaperon analysis? Why would France’s Direction générale de l’armement / Techniques aéronautiques (DGA) release photographic data to ATSB and yet chose not to make Flaperon Analysis findings public after such a long period of elapsed time?

To sum up, a close examination of the flaperon’s breakage points does not yield any comprehensible explanation for how it came off the plane, commensurate with a terminal plunge into the southern Indian Ocean.

This is baffling but unsurprising. Every time we look at the debris data carefully, we find that it contradicts expectations. The barnacle distribution doesn’t match the flotation tests. The barnacle paleothermetry doesn’t match the drift modelling. The failure analysis doesn’t match the BFO data. And on and on.

Something is seriously amiss.

295 thoughts on “How Did MH370’s Flaperon Come Off?”

  1. @Jeff Wise

    I don’t think we can expect a detailed failure report on the flaperon from the French any time soon.
    The French are treating the disappearance as a criminal case, not as a regular aircrash investigation.
    Their silence rather could be telling for it could mean they still have reasons to believe it was a criminal act.

    But then imo we actualy don’t need the flaperon to provide the essential answers how those pieces failed and seperated.

    The ATSB has the outboard flap section which shows similar damage and failure.
    Malaysia has all the other pieces.

    IMO @HB’s question would better be directed to the ATSB and Malaysia; ‘Why would the ATSB and Malaysia not make all their debris-analysis public after such a long period of time?

    From the French I can understand it but from the ATSB and Malaysia surely not.
    I can hardly imagine they don’t have the conclusive evidence already.
    And if they are not sure yet why don’t they allow independent investigation??

    Is there something essential to hide?
    This a very understandable question in this situation.

  2. Is it possible that this particular damage actually occured while the flaperon was floating at the sea surface? I guess that waves and wind during 15 months period can produce persistent cyclic lateral forces. That can maybe explain why barnacles were found on the side of the flaperon which was above the water, if you add the weight of parts which were torn off in the sea.

  3. Jeff:

    You say: “This is baffling but unsurprising. Every time we look at the debris data carefully, we find that it contradicts expectations. The barnacle distribution doesn’t match the flotation tests. The barnacle paleothermometry doesn’t match the drift modelling. The failure analysis doesn’t match the BFO data. And on and on. Something is seriously amiss.”

    Well, to many others, it is not that baffling. The debris does not contradict expectations. In fact, it tells a story completely consistent with impact somewhere along the southern 7th arc, with at least some of it resulting from inflight separation. The new Inmarsat file contains further evidence that there was no material BFO error at 00:19, so there was a very high speed involved after FE.

    The flaperon failure analysis, which indicates inflight separation (whether due to flutter or other fatigue modes induced by high speed) does match the 00:19 BFO derived descent rate implications.

  4. The debris was over a year late after the investigators started to call out why none was found so mysteriously just a few showed up (to suppress this vocal outcry) by then they could have reverse engineered/modelled hot spots to deposit the least amount of pieces that match the 7th arc theory.

    something is very amiss with the flaperon analysis as it can not identify how the crash occurred !

  5. @ALSM
    You stated “The flaperon failure analysis, which indicates inflight separation (whether due to flutter or other fatigue modes induced by high speed) does match the 00:19 BFO derived descent rate implications.”

    A detailed debris analysis should be able to confirm.

    Regarding flutter, the flutter issue is when the aerodynamic loads frequency reaches the natural frequency of the wing or control surfaces, if the airplane accelerates, the frequency will increase away from the natural frequency of the component until you reach other natural frequency oscillation modes. Flutter could be an issue if maybe the speed is constant and the frequency matching the natural frequency of the components (usually narrow).
    Also airplanes are designed for a dive scenario (including flutter and fatigue failure modes) as governed by the Design Dive Speed which is much greater that Design Cruise Speed. According to this guideline (https://www.faa.gov/documentLibrary/media/Advisory_Circular/25-335-1a.pdf), it should be a minimum of M=1.05. The exact value is not published.

  6. @Ge Rijn. About debris items 9 & 15, the closing panels above the flaperons, being pushed off by water pressure, you say, “Imo the only combination of forces that could have done that are the forces that occurred during a ~level, low AoA, ditch-like entry on a water surface.”

    On magnifying the debris analysis for these items I see fracture lines in the bottom skin just in front of the seals. Under just RAT the left flaperon would have been up 10 deg, from neutral the right in neutral, the flaperon cove (flap airflow entry) doors closed, so water in quantity would have to break through. It may be that the flaperons forced them off on separating?

    About the flaperon hitting the flap, my current interpretation is that before that and while the auxiliary track (‘rail”) and its rib-mounted carriage assembly were intact, there was outboard movement of the flap coincident with the flap being forced up, possibly more than once.
    I notice talk of a side force on the flaperon, which could be related but have drawn a blank on that so far.

    @HB. You said, “if there was such a shift in axial load, I would expect the FRP to buckle or honeycomb composite to delaminate as the FRP/honeycomb composite” You were going to look for signs of that.

    You might be alluding to the stresses in the skin and structure if the flaperon lost its trailing edge, consequently rotated aft and was torn off.

    To avoid ambiguity I do not suggest that happened. My hypothesis aimed to demonstrate that loss of t.e. would lead to such rotation before flaperon separation. However that would be inconsistent with the ATSB conclusion that both flaperon and flap separated from the neutral/retracted position ie not rotated.

    So if the ATSB conclusion stands and the hypothesis is accepted then the t.e.did not separate before the flaperon.

  7. @Ge Rijn
    I totally agree that investigation of the debris in hand can lead to further clues. Two possible investigation routes in my view:
    * study possible dive speed and compare with the structural performance (including resonance frequencies of components and Design Dive Speed) of the aircraft.
    * more indepth analysis of debris including radiography / UTS inspection to determine actual failure modes (rubbing, bending, bluckling, axial impact, bottom impact, fatigue, yield etc.).

    I also agree that an independent investiation would have its on merrit.

    @David, no apparent sign of buckling or delamination from the naked eye.

  8. @HB. Now flutter. You may know whether the aircraft flutter boundary supposes all hydraulic actuators (PCUs) are operative, or just those that are RAT powered; or no hydraulics at all? The actuators whether powered or inactive but ‘blocked’ (hydraulically locked) will constrain any flutter tendency. Indeed many are blocked when without hydraulic pressure (or damped when an actuator is inactive) for that reason. But not the flaperons’. Under RAT powered hydraulics both the left’s would be in bypass, ie free, as would the right’s inner. The right’s outer would be active.
    So if the flutter boundary is based on no hydraulics, having one flaperon actuator active would extend its flutter boundary even beyond certification limits, the APU further yet again.
    The certification boundary supposing thee were RAT hydraulics would be no different since that would not protect the left flaperon.
    If the boundary supposed full hydraulics then both flaperons would be vulnerable within the boundary.

    Nominally though a boundary of M=1.05 should rule out flutter.

  9. Jeff, thank you for revisiting the MH370 Flaperon Failure Analysis (v3.0).

    I strongly encourage your readers and contributors to take a minute and carefully examine section 12.0 Supplemental from the Analysis that covers Asiana Airlines Flight 214 (a Boeing 777-200ER) that suffered Flaperon damage due to impact with ground (not flutter type damage)

    The lack of an official report from the French is most frustrating, mostly because this is NOT a complex failure analysis for seasoned investigators. To put it bluntly; people, governments, and corporations have known for MANY months EXACTLY how the Right side Flaperon separated form MH370! That fact in itself makes one’s head spin. Thank you for raising awareness to this odd behavior by the authorities. The silence raises an unlimited number of questions and concerns.

    Time permitting (and if the French do not release official findings) we plan on a future revision that will include studies using Finite Element Analysis (FEA) of key primary attachments as failed on MH370. This final analysis may exhaust the ability to perform analysis from public photos and limited available data, but may hopefully increase confidence in the analysis as a whole. It could also bust the analysis, regardless, my bruised feelings aside, it is the truth we all desperately seek.

    All ideas and constructive feedback welcomed.

  10. The right flaperon and the inner portion of the right outboard flap broke off together when the airplane hit the water.

    Simples.

  11. @Kenyon,

    In case of Asiana Airlines Flight 214 we have a combination of seawall impact + ground impact. The engine seemed to have detached from the wing frame without causing much distortion to the wing primary structure. Crashworthiness design principles would be that the engine mounts would sustain the impact and engine remain as far as possible attached to wing primary structure to minimise say fire escalation. Here we have an example where the engine detached without much deterioration of the wing elements. BA37 also show the engine still in place and no damage to wing components.
    Ignoring for a moment the hinge issues and the jagged edges, i am wondering whether a very soft ditching such that the engine failure did not lead to distortion of the wing structure could be compatible with the trailing edge damage (rubbing failure mode?).

  12. I still think the damage on Flight 1549 (the Hudson ditch) makes the best comparison with the ‘damage-picture’ we have from MH370 till now.

    Also with Flight 1549 the first section of the outboard flap broke away (even on both wings). Substantial damage was done on wing related surface control trailing edges.
    The right wing aileron shows similar trailing edge damage like the MH370 flaperon and outboard flap section.
    This 1549 right wing damage was not caused by a seperating engine for the right engine stayed attached.
    Also on 1549 the inner outboard flap flap fairing was broken and a big piece of it missing like with MH370.

    Scroll down in the following link and take a look at the pictures:

    http://cluesforum.info/viewtopic.php?f=25&t=764&start=45

  13. Like to add that also the left wing aileron seperated with Flight 1549 and the right wing engine shows damage to its cowlings with big pieces missing that clearly remind me of the chunks of engine cowling found from MH370.

    The pattern is quite obvious to me. The fast majority of pieces found till now from MH370 and their kind of damage are just like the pieces and their damage affected during the 1549 ditch.

    Only the conclusive proof is still missing.

  14. An excellent article Jeff.

    Two things that have always struck me about the flaperon:
    – No other debris was found in a similar time period and place.
    – The speed with which the French acted to transport it to Paris.

    Was it planted?
    More outrageous: were the French expecting it?

  15. @Ge Rijn

    Agree completely with substantial damage to the trailing edges in flight 1549. In fact more so than 9M-MRO. At about 1:49 in this video;

    https://www.youtube.com/watch?v=tNpGWlUzGXQ

    Though I believe with the Hudson ditch flaps were deployed and the ATSB has stated that the outer flap of 9M-MRO was retracted “on impact”. I cannot see any lateral damage to the hinges as described by @HB.

    The other unusual thing about the flaperon story was the early and honest call regarding its origin by the MAG. This compares with other pronouncements such as the suggested South China Sea and Cambodia crash sites as well as the infamous Lido graphic.

  16. @Simon, Thank you! Having read some of the internal reports prepared by French investigators, I think they’re as baffled by the flaperon as the rest of us. It’s worth noting that they explicitly noted the inconsistency between the barnacle distribution and the observed flotation behavior, and so generated drift scenarios based on each case separately since they are incompatible.

  17. @David

    On your comment; “Under just RAT the left flaperon would have been up 10 deg, from neutral the right in neutral, the flaperon cove (flap airflow entry) doors closed, so water in quantity would have to break through. It may be that the flaperons forced them off on separating?

    I don’t think so.
    Item 15 shows on both sides it was ripped off from its attachment rails ripping the fasteners through the skin leaving them at the attachement rails which then must have stayed in place.
    If the flaperon pushed this fixed panel out when in retracted/neutral position the flaperon would also have pushed those attachment rails up and probably broke them together with the panel leaving pieces of attachement rail attached to the panel.
    This obviously did not happen.

    Also the flaperon upperskin shows no signs of those attachment rails which imo would have left damage or inprints in the upperskin at the places where the flaperon would have pushed against those rails and panels.
    You can clearly see the edge where the seals of those panels mark the edge of the area of the flaperon which would have been covered by the fixed panels when retracted.
    There is some damage in the upperskin but not in the areas where those rails would overlap the flaperons leading edge when retracted.

    Imo this can mean two more likely scenarios;
    Or the flaperon was not retracted and the cove door open with water pushing through the gape.
    Or the panel broke away shortly after the flaperon seperated by the force of water pushing it through its fasteners.

  18. @Kenyon, My pleasure, you’ve produced a very insightful and thought-provoking piece of work. I agree with you, it’s very frustrating that the French have been so furtive about the flaperon. They’ve shared their reports and samples of the barnacles with the Australians/Malaysians, but have said very close-lipped to the public.

  19. Airbus and Boeing have different approaches to flight control. They also have differing engine attachment methods, safety strategies, and connection strengths.

    Attempts to analyze MH370’s B777 right side Flaperon damage characteristics by siting examples of Airbus incidents (or even non-B777 models) control surface damage as definitive evidence of the failure mode for MH370’s right Flaperon and then use such examples to present MH370’s definitive end of flight scenario seems to weaken such theories.

    @HB,
    Thank you for the comments. FWIW, my gut feel is that (in a perfect scenario) the RR engines on the Boeing 777-2H6ER would break free during a piloted, controlled, wings level, water landing attempt. I also suspect the engines would have a propensity to rotate forward & up and pass over the top of the wing. (Naturally with unpredictable wave/wind conditions at sea, unlimited methods of ‘ditching’, there’s absolutely no telling…)

    I understand (in extreme layman terms) that Airbus engines are designed to stay attached more so than Boeing engines. There are differing safety mitigation strategies between the two aircraft producers.

    My recollection of Asiana Air 214 was that the tail section suffered damage from sea wall but wings cleared the wall.

  20. @All

    The nature of this debris is very unusual, for a number of reasons. Possibly, this is telling us that the way the aircraft impacted the water also has to be very unusual. Then, if it was being piloted at the time, and deliberately crashed in such a way as to leave as little floating debris as possible, but to also ensure it sank as quickly as possible, then perhaps its not so surprising we have such an odd assortment of debris to consider?

    Items 9 and 15 are possibly the most intriguing pieces of all. They are in a similar condition, so must have separated from the wing in similar circumstances. The RH flaperon and RH outboard flap section were both ripped off, together with most of No7 flap track/hinge fairing, so what happened to the LH flaperon? There is no straightforward answer, especially as the aforementioned item 9 LH flaperon fixed panel was ripped off!

    I used to think that the flaps and flaperons had to be extended in order to produce the RH flaperon trailing edge damage. I now go along with the ATSB, and believe they were retracted at the time.

    Possibly the aircraft was side slipped into the water, right wing down, with very little forward velocity. This might explain the lateral force in the flaperon as proposed by Tom Kenyon. It would also account for the RH forward fuselage damage as evidenced by the Rodrigues interior panel, and the right engine pod fragment (the piece with trunking attached)

    Gyesbright said it was simples. Unfortunately, it’s far from simples.

  21. Re my previous post – item 9 LH flaperon fixed panel, should have read item 15 LH flaperon fixed panel.

  22. @Ge Rijn. “..the flaperon would also have pushed those attachment rails up…”

    As you say there is no sign of contact between the rails and the flaperon. The flaperon would lift into panel seal edges well before contacting the rails but I agree that if still fully forward it well could hit the rails too. However it need not have been fully forward.

    Still overall that is not a front runner.

    Adding to your ditching possibilities, forceful water impact could force the cove doors open since the linkage does not look strong.

    Yes, the flaperons down would expose them though the evidence currently is against that.

    Just to simplfy things further (!) there are the possibilities too of air pressure from outside-the-envelope “g”, or shock.

  23. @Kenyon – I understand the tail was submerged in water before striking the seawall… so it might be the wings trailing edge parts struck the upper seawall?? the trailing edge parts might include the flaperons also the landing gears.

  24. @MH – My memory recalls that the main landing gear clipped seawall and sheared of per design and the tail section hit soon after and separated. I don’t recall any portion being submerged. In addition I don’t recognize the significance or relevance to MH370 flaperon damage.

    I think the important takeaway is that the left flaperon smacked the ground during the deceleration and rotation sequence of the aircraft as it came to rest. It did not suffer damage due to flutter or similar cyclic fatigue conditions.

  25. @kenyon- if the Asiana flaperon damage was some what similar to the MH370 flaperon then perhaps mh370 hit a semi submerged reef on decent.

  26. @MH-there would not be a submerged reef in the middle of the ocean. And if it indeed hit a submerged reef, it would been close to land and plenty of other debris would have shown up at the time.

  27. @David

    Yes, I guess the cove doors could have collapsed also under water pressure when closed. Air pressure or Mach-like shock-waves seem very unlikely to me.
    As stated earlier; during the SilkAir and ChinaAir747 near Mach dives (and China Air pull-out) no wing parts detached only tail pieces.

    Panel 9 and 15 where ripped out upwards through their fasteners off their attachment rails.
    Take a look at page 4 of the latest MOT debris report:

    http://www.mh370.gov.my/phocadownload/3rd_IS/Debris%20Examination%20300417.pdf

    You can see how far this I-shaped rails are stretching towards the edge of the panels.
    To me it’s clear the forces who seperated them came from underneath and those forces must have been the same who seperated the flaperon, the outboard flap section and all other wing related parts.

    When the flaperon was retracted it could not have avoided hitting those rails with great force imo and not break them or not leave marks/damage on the upperskin of the flaperon.
    The panels came off upwards from the rails so the rails must have stayed attached.

    The same goes for the outboard flap section.
    When retracted the spoilers and their actuators are above the leading edge.
    When pushed upwards with force this leading edge would crush into those actuators and spoilers when the ouboard flap was retracted when it seperated. Leaving marks and probably damage in the upperskin of the leading edge.
    None of this is visible in the pictures on the places you would expect this.

  28. And to add; while panel 9 is from the left wing and seperated the same way as panel 15,
    I will not be suprised when the left wing flaperon seperated the same way as the right wing flaperon and is still floating somewhere or lying on a shore waiting to be found.

    I hope so.
    BTW, it’s a long time ago now since the latest found piece was reported..

  29. @David
    @GeRijn

    David, I think you’re really on to something with airloads! It would explain the symmetry concerning items 9 and 15. Excessive airloads during a high speed descent would affect both wings equally – these particular fixed panels could be more vulnerable to separation under excessive airloads, than other wing panels. Whereas, a water impact os much less likely to show such selective symmetry in its effects.

    With the RH flaperon itself, airloads or possibly flutter (yes flutter) would explain the hinge damage better than a water impact. Again there is symmetry in the way the two hinges failed.

  30. @ROB @David

    You’re right about the symmetry in the way and positions panel 9 and 15 have seperated but those panels are fixed panels on the top side of the wing.
    They are not vunerable for flutter or high airloads for the panels are tight fixed and high airloads would be on the underside of the wing. And with retracted flaperons those panels would be shut of from those airloads by the flaperons and cove doors.

    The flaperons did not push those panels out either for they would have to push them out through their attachment rails, braking those rails and leave remnents on the panels.

    This did not happen for the panels were ripped off by another force upwards coming from underneath ripping them from their attachment rails through their fasteners.

    The symmetry between panel 9 and 15 in damage and position (left wing, right wing) tells me the same kind, strenght and direction of forces ripped them out.

    Imo this could only have been water forces coming from underneath when the plane hit the water in a wings-level and horizontal attitude.

  31. I like @ROB’s thinking. If this was a piloted fight to the end, it could have included some unconventional maneuvers that resulted in a difficult to explain debris trail.

    Right now most people are assuming it was ghost flight falling out of the sky from FL350. Even many in the pilot-did-it crowd are saying the pilot just flew until fuel exhaustion and the let the aircraft fall out of the sky. Which is of course possible, but not the only possibility.

  32. @MH

    There seems to be some confusion.

    The damage to Asiana Air 214 flaperon is not the same as MH370 flaperon’s damage.

    This damage analysis is covered in the “MH370 Flaperon Failure Analysis” referenced by Jeff in the main article.

  33. @Kenyon

    Yes, the Aisiana 214 damage is quite different while it struck land. A flat static surface.

    I would like to repeat the parodox Jeff is discribing in his topic:

    “Recall that two scenarios have been proposed for the flaperon coming off 9M-MRO: either the plane hit the water, or it came off as the result of flutter in a high-speed dive. Neither event could reasonably be expect to produce a primarily lateral (that is side-to-side) force on the flaperon of the kind Kenyon describes.”

    Like to add a part of the sentence Jeff left out:
    ” or repetitive lateral (or torsional) movement of the hinges in the inboard/outboard direction.”

    I suggest repetitive lateral or torsional movement in the hinges together with repetitive up and down movement could have occured when the flaperon skidded for a lenght of time on a water surfuce which has almost always a wave-like structure.
    Repetitive forcefull sideways movements combined with repetitive with forcefull occilating up and down movement could then have caused overstressing and fatigue in the hinges after a short time.
    And then when one fails the other will break right after by the rotating torsion caused by the parting flaperon on one side.

  34. @Ge Rijn, Given that the flaperon is directly behind the engine, I can’t see how it grazes through the tops of the waves. Either the tail or the engine cowling is going to hit first, at which point the whole plane slams into the water.

  35. Impact on water exposes airplane structural elements to pressures that are nearly a thousand times greater than the airloads it is designed for (seawater density is about 840 times that of air). There is really no need to theorize about flutter and fatigue damage.

  36. just a thought as the end of flight is said to be a spiral downward to impact, perhaps the aircraft rotated with right wing down entering the ocean with forces greater than a ditching on its belly.

  37. @Jeff Wise

    Yes, in a level ditch-like ~low AoA entry on the water the tail and engines would hit the water first but don’t necessary have to slam the plane immediately into the water. In the Hudson-ditch this did not happen. The plane plowed throught the surface a considerable lenght still under a low AoA. And one engine stayed attached.
    Those engines don’t have to shear off by definition and would cause a whole lot of water turbulance hitting the flaperon in their wake too.

  38. @Ge Rijn, Point being, there won’t be direct contact between the flaperon and waves. Spray, maybe, but nothing periodic, as you had proposed.

  39. @Ge Rijn.”..high airloads would be on the underside of the wing. And with retracted flaperons those panels would be shut of from those airloads by the flaperons and cove doors.”

    Take the pressure under the wing as P1 and above P2. The pressure under the closing panels will be between those depending on throttling of both inflow and outlow in the gaps to and from that space but it will be higher than P1, thereby lifting the panel.

    The closing panel designer will know what P2 and P1 are at the aircraft envelope design limit and from the throttling dimensions what the pressure under the closing panel will be. He will design the panel strength and fittings around that or at least see to it that the panel will not be overloaded by that if the design point is say with flaps down.

    The difference between P1 and P2 are dependent on the air density and square of speed at a given angle of attack and also on the AoA itself. In pulling high ‘g’ in a high speed descent, particularly at low altitude the aircraft could well go beyond the flight envelope it has been designed and cleared for.

    Depending on what set the design point, altitude, ‘g’ and speed the closing panel then might be overstressed and pop off.

    It is also conceivable that should the flaperon detach the turbulence and vortices back there could add to their loading.

  40. For those interested, the Broadbent number and criteria are typically used to assess whether flutter occurs or not. Note that Design Dive Speed should be as per general design guidelines over M=1 and cover transonic flutters. The Broadbent Number B = 2 x Pi x f x c / v where c is the reprentative cord of the component B777 here is about 5-6 m, f is the natural frequency typical values are 10Hz-200Hz (high range for small elements such as flaperon and low end for large element such as wing), v is the true air speed. If B is higher than 1.5 for control surfaces, flutter is not expected.

    @Kenyon, maybe if you envisage FEA, a natural frequeny run on the wing component and wing assembly would be useful.

  41. @ Jeff Wise
    This is a great article, please keep up the good work.

    BTW, I’ve noticed that in relation to MH370, you touch mainly issues that are of a scientific nature.

    However, there is also the legal proceedings that are happening re: MH370.

    For example, the multiple lawsuits filed in the US regarding MH370 have now been consolidated in a DC court before a trial judge.
    See link:
    http://www.jpml.uscourts.gov/sites/jpml/files/MDL-2712-Initial_Transfer-05-16.pdf

    And according to a news report, the judge has ordered MAS to reveal what it knows about a ‘third party tortfeasor’ who was responsible for the plane’s disappearance.

    http://www.adelaidenow.com.au/travel/travel-news/malaysia-airlines-ordered-to-reveal-third-party-involvement-in-mh370/news-story/1a0242467d9c971e95f00a82c6443aa5

    It appears that MAS is keen on getting the case dismissed from US courts on jurisdictional grounds.

    There is no limit to liability in some US courts, and the Insurance companies are also keen on keeping the liablities to a manageable amount.

    A very article on Fortune for example says the following:

    But in the case of MH370, unless they find the airplane, the cockpit voice recorder, and the flight data recorder — and those devices can categorically prove terrorism or some other form of negligence — there’s a distinct possibility these families will get little or nothing above the standard $175,000….
    And at least for the moment, Lloyd’s and Allianz may be off the hook for more serious damages. While there is no information or hard evidence to suggest it wasn’t terrorism or criminal negligence, there is also no information to suggest it was. From a financial perspective, some of the parties facing the most risk would be better off if the plane is never found.

    http://fortune.com/2014/05/01/the-big-money-surprise-about-malaysia-airlines-flight-370/

    So it appears that MAS and it’s insurers may like to keep the plane ‘disappeared’ as well.

    And earlier this year, The Guardian had this piece:

    The MAS spokeswoman said the restructure was determined to be in the public interest “to ensure the continued existence of a national carrier … The objective of the restructuring has never been to frustrate the legal process or avoiding its responsibilities, as it has been inaccurately portrayed.”

    She added that, “notwithstanding that MAS is now in administration”, it had adequate insurance coverage in place “to meet all of the airline’s legal liabilities arising from the loss of flight MH370”.

    The spokeswoman did not reply to a follow-up question asking how the airline could be sure its coverage was adequate when the extent of its liabilities had not been determined.

    https://www.theguardian.com/world/2017/jan/18/compensation-battle-stalls-for-families-of-mh370-victims

    So MAS may actually be determined to not pursue the search for the plane.

    Also, the liabilities arising from the shoot down of MH17 can now be determined to some extent. So what is the implication for MH370?

    Jeff, hope you can write something about these issues as well, keeping in mind any legal consequences of course, so we can all make some sense of them too.

  42. @David

    Yes, I thought of that too. I mean airloads forming during a pull-out from a steep dive on the underside of the wing.
    I had ChinaAir 006 in mind.
    Although a Boeing 747 the plane pulled-out of a vertical near Mach dive excessing 5G of structural loads. No wing panels or wing control surfaces seperated. Only pieces from the tail. The wings were bend 5cm upwards on their roots;

    https://en.wikipedia.org/wiki/China_Airlines_Flight_006

    I don’t think those kind of airloads, if they also occured on MH370, would have seperated the flaperon, the panels, outboard flap sections, aileron(s)trailing edge, other wing panels, flap fairings etc. on MH370 either.

    And when the flaperons were retracted in such a steep dive/pull-out event (which they must have been) the panels would have been isolated from those heavy airloads.

    But like you say, if the flaperons seperated first during such an event those panels would take the full force of the airloads too and could probably have been ripped out.
    I cannot rule this out but regarding the whole debris and damage picture it seems highly unlikely to me.

    A ditch-like water entry makes a lot more sense to me. Even a AF447 kind of belly landing/crash would make more sense.
    But in the latter case, where is all the other debris if something like this happened also to MH370?
    And why are only mostly trailing edge/surface control/wing and engine related pieces found till now?

  43. @Kenyon

    I also want to question your following statement:

    “No significant evidence of secondary structural damage excludes a massive trailing edge strike and leads the author to conclude that the Flaperon separated from MH370 while in the air and did not separate from the wing due to striking water or land.”

    Since the flaperons trailing edge is roughly 1/3 of its total lenght and is not supported by internal ribs but as whole attached to the end spar of the flaperons main structure by fasteners, I rather think the trailing edge would break away at this end spar before causing deformation in the flaperons main structure.
    And this is what you see in the pictures.

    Imo you can even see in the angle and pattern of the break lines along the upper and bottom skin at the end spar of the flaperon, the trailing edge must have broken away upwards.
    Telling me forces that hit the underside of the trailing edge/flaperon broke it away.

    In this case the upwards torsional forces on the hinges must have been huge. And if those forces were oscilating and caused lateral movement also, tension-stress and fatigue could have added to the breaking of the hinges at that point too imo.

    Concluding a massive strike or series of (oscilating) strikes on the trailing edge/flaperon underside can not be excluded imo.

    Like to hear your (and others) opinion on this.

  44. @CliffG
    I agree with your implications. I saw the 3rd party hijack claims a few weeks ago. I am thinking Malaysia is possibly getting ready to say they think it was 3rd party hijacking, but presumably without any solid evidence of such. Of course, we’d welcome any proof of that.

    But I just feel like it’s getting close to the time where we have say apparent likely cause(s), so that may be Malaysia’s choice of cause.

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