Implications of the Absence of MH370 Debris on the Coast of Western Australia

Implications of the Absence of MH370 Debris on the Coast of Western Australia

Richard Godfrey and Duncan Steel
2016 May 11
Updated May 12

 

Introduction
Several different people/groups have published reports on the drift modelling of floating debris from MH370. Brock McEwen’s Comparative Analysis of drift studies (2015 December 07) is available here. Most recently (2016 April 25) he has published MH370: Probabilistic Analysis of Shoreline Debris, which is available here.

There is an important conclusion in McEwen’s report, which prompts the present post here. He finds that, based on modelling carried out by researchers at the International Pacific Research Center (IPRC) at the University of Hawaii, if the crash occurred in the priority search area then there should have been dozens of items of MH370 debris found on the coast of Western Australia by now, and yet there have been no such confirmed identifications. As McEwen states in an email message, “The bottom line seems inescapable: either IPRC’s probabilities are wrong, my model is wrong, or the current search area (36-40 degrees south latitude) is wrong.

(Note that, as described below, the IPRC extended start line for their drift modelling stretches from 34S to 37S; however, it is non-coincident with the 7th arc, as McEwen pointed out, but rather lies some distance to the northwest of that arc, as is confirmed below.)

The core question that is addressed in this post is as follows:

Can we reconcile the discovery of debris in the western Indian Ocean along with the non-discovery of debris on the coast of Western Australia with a crash location on or near the 7th arc, and if so what does this tell us about where the crash occurred, in terms of the latitude (near the arc)?

 

An Omission from the First Version of this Post (May 11)
It is noted that an analysis by Henrik Rydberg published in early-August 2015, soon after the flaperon was discovered in La Réunion, addresses all the essential points covered in the present post, and more; we apologise to Rydberg for having omitted to mention his analysis in the May 11 version of this post. Further discussion of Rydberg’s conclusions are included at the end of this post.

 

A few background comments
Working out likely end-points for floating MH370 debris from any putative crash location on or near the 7th arc between 29S and 40S can be very confusing.

Whilst the West Australian Current (WAC) would be expected to pick up such debris and carry it initially north-east, this does not imply that any must end up on the coast of Western Australia (WA). (Note that the “coast of WA” in question here is limited to that facing west onto the Indian Ocean, and not the coast from Albany eastwards, nor that eastward of, say, Port Hedland or Broome.) The WAC trends anti-clockwise and feeds into the westward-flowing South Equatorial Current (SEC) which would then be able to take floating items to locations where MH370 debris has been found in the western Indian Ocean (Réunion, Rodrigues) and on the African coast (Mozambique, South Africa), with some passing to the north of Madagascar and some to the south. Some items will turn southwards out of the SEC before reaching the longitude of Madagascar, and some others will make that turn (continuing anti-clockwise) in the Agulhas Current off the southern coast of South Africa, and then return in another year or so from now to the approximate region where they started (i.e. the MH370 crash site).

Returning to the WAC and the floating debris carried in it, the flow is broadly parallel to the WA coast, and northwards. Between the WAC and that coast, however, is the Leeuwin Current (LC), which flows southwards, largely over the continental shelf (which extends a long way westwards from the coast, especially at latitudes north of Geraldton). As the Wikipedia page for the LC says, “The West Australian Current … produced by the West Wind Drift in the southern Indian Ocean … flow[s] in the opposite direction, producing one of the most interesting oceanic current systems in the world.”

What this would appear to mean is that for debris from MH370 to reach the coast of WA (so as to be found there on the beaches or rocks) it must drift slightly eastwards out of the general WAC and then be picked up by the counter-flowing LC, and make land from there. A partial barrier to this is posed by upwelling at the edge of the continental shelf; such upwelling also occurs at Broken Ridge.

An immediate response to the above overall picture (if it is correct) is that the places one would look for MH370-derived items might be the islands of Shark Bay, and the reefs of the Houtman Abrolhos further south, off Geraldton. However, there will be others with far better knowledge of where jetsam and flotsam tends to wash up, and its origins.

 

The IPRC start locations are not on the 7th arc
The IPRC researchers state that their assumed source (i.e. range of start positions in their drift study) is “equi-distributed between 37S and 34S along the 7th arc” (e.g. the caption to their Figure 2 on this webpage). However, this appears not to be the case, as was indicated by McEwen (see Figure 19 in his Comparative Analysis). As he noted, the extended source used in the IPRC study seems to be a line that is curved, and is inside the 7th arc but is not parallel to it; the line does run from 37S to 34S though.

To confirm the location of the IPRC-assumed source (set of starting points) their Figure 3 (which plots their source line with a white background) was georeferenced, converted into KMZ format, and brought into Google Earth. The resultant screen grab is shown below, with the 7th arc at 35,000 feet plotted in red for reference.

(For anyone who wants it, the KMZ file for that IPRC line is available here; and the 7th arc KMZ file is here.)

IPRC_arc

Figure 1: The red line indicates the 7th arc for an assumed altitude of 35,000 feet, and the broad black line shows the IPRC-assumed source for drift modelling, which lies about one degree to the northwest of that arc.

The reason for this discrepancy is not known at this stage. Obviously such a simple error leads one to question the veracity of the overall results obtained, but for present purposes it will be assumed that the IPRC drift modelling outcomes do indeed represent what might be anticipated to occur given the extended source location shown above.

It might be noted that, naïvely, one might suppose that floating items modelled as starting from the IPRC source would seem less likely to reach the coast of WA than items actually starting their drift further east, on the 7th arc.

In passing it is noted that it is unfortunate that the IPRC drift modelling results as publicly available are aggregated for all points along their line between 34S and 37S; it would have been useful to be able to compare results for, say, start points at 34S, 35S, 36S and 37S, as will become clear from the discussion below.


Drift Modelling Analysis
The drift modelling described here makes use of the Adrift website. The coast of WA was defined for locations between 22S 113E south to 34S 114E as shown in the far left column in the table below.

 

RG11

Table 1: Drift probabilities and earliest arrival times on the WA coast for different assumed start locations near the 7th arc. 

For each assumed point of origin of debris between 27S and 39S near the 7th Arc (longitudes rounded to the nearest degree so as to fit against the required inputs for the Adrift model), the earliest time when the coast was reached was determined. These times (the model uses two-month jumps) are shown in the table above, along with the associated probabilities of reaches those points on the coast from the stipulated starting positions.

It is emphasized that the results appear ‘noisy’, with apparent jumps in probability that seem unphysical, some coastal locations being indicated to have zero probability of receiving debris whilst adjacent locations have substantial values. The results can therefore be regarded only as giving some general indications of what may have occurred.

This noisiness can be easily seen in the chart below, wherein the total probabilities of reaching the shore of WA for each origination point are plotted against the latitude of those start points. A tentative deduction from the best-fit curve shown is that there is a lower likelihood of reaching the WA coast if the crash location were not near the extreme latitudes shown, with the minimum in the curve occurring for latitude 32S, and the minimum in the output data at 34S.

 

RG10

Figure 2: Summed drift probabilities to the WA coast for different assumed start locations/latitudes near the 7th arc. 

A fundamental observation we are trying to explain here is the fact that MH370-derived debris has been found in the western Indian Ocean, but not on the coast of WA. We should be comparing derived probabilities, therefore.

For an origin (i.e. putative crash location) at 34S, 94E the summed probability for the WA coast in the table above is just 0.00063. From other locations on/near the 7th arc the values are around 0.002 or higher (i.e. summed WA coast probabilities). By comparison, for the ‘No Step’ item found in Mozambique the maximum probability calculated was 0.00202, starting from 30S. For the flaperon found in Réunion, the maximum possibility derived was 0.00134, also for a start at 30S.

On this basis it might be concluded that for the least amount of debris to land on the West Coast of Australia, the most likely MH370 crash location is around 34S 94E on the 7th arc. Further, the low probabilities of debris starting there and arriving there on the WA coast are not inconsistent with the discovery of debris across the Indian Ocean to the west.

 

Further Discussion
Obviously we would like to understand the above results in terms of how they come about, in case insights might arise that assist the search for the MH370 crash location.

What may be significant is that the 7th arc is close to the east-west divide in ocean currents, for the two months after March 2014. Consider the location identified above (i.e. 34S 94E) as being the least-likely to result in debris reaching the WA coast. The drift path from that point indicates a most-likely heading that is north-westerly (azimuth around 308°).

That value is shown in the table below. In this table are mapped the highest-probability drift directions derived from the Adrift model for the two months commencing March 2014 as a function of initial latitude and longitude. The boxes coloured red indicate the approximate 7th arc (rounding to the nearest degree being necessary). The yellow boxes indicate locations that might have been reached should MH370 have been glided on a continuation of its flight path after fuel exhaustion at the 7th arc.

 

RG6

Table 2: Drift directions for different start locations across the two months starting with March 2014.

 

Whilst the directions tabulated might be regarded as being somewhat scattered, reflecting the vagaries of current flows and eddies (and note that in some locations the most-likely behaviour is that floating debris would go nowhere during those two months; i.e. it remains ‘Still’), in broad scope the values in the upper left parts of the table indicate current flows that are generally northwest, whereas those in the lower rights parts of the table indicate current flows more towards the northeast. This is not unexpected, being reflected in the anti-clockwise flow of the WAC.

For example, a crash point at 35S 95E (about 78 NM outside the 7th arc) would normally correspond to the equivalent controlled ditch end point (if fuel exhaustion occurred at 34S 94E). However, 35S 95E is on the other side of the east-west divide in ocean currents and therefore debris will not drift back toward 34S 94E, but rather head off in a north-easterly direction around 052°. The general pattern being an anti-clockwise path, most of the debris that starts off heading north-east will eventually circle round to a northerly, then westerly path.

For those points between 32S and 36S on and just inside the 7th arc the highest probability drift direction for the two months from March 2014 is westward; outside the 7th arc, though, the drift pattern changes to an easterly or north-easterly direction. An initial north-easterly path will still reach the locations of the various finds made to date, it will just take longer to get there than an initial north-westerly path.

 

Concluding Remarks
Obviously the situation is complicated, and deserves/requires further study. The general picture arrived at, however, is that if the crash of MH370 occurred on or inside the 7th arc between latitudes of 31S-36S then the resultant floating debris may be anticipated to have drifted initially towards the northwest and then been transported across the Indian Ocean by the SEC; under this circumstance it seems that debris arriving on the coast of WA is unlikely, possibly explaining its non-detection.

On the other hand, if MH370 crashed outside of the 7th arc between 31S-36S, or on the arc but further south, then floating fragments are more likely to have drifted to the coast of WA. The non-discovery of debris there argues against such crash locations, therefore.

In 2015 August, on the basis of the flaperon found on La Réunion, Van Gurley (Metron, Inc., Reston, Virginia) suggested that the underwater search should be shifted about two degrees northwards from the ATSB priority search area.  That is, the identification of debris from MH370 in the western Indian Ocean may be interpreted as being indicative of a crash location not so far south as 36-40S, but a few degrees further north, a suggestion that we confirm here. Further, we find here that the  non- identification of debris on the coast of Western Australia may be interpreted as indicating a crash location that is on or inside the 7th arc, which may be regarded as being additional evidence against any scenario in which MH370 is thought to have continued for some distance beyond the 7th arc.

All readers are urged to refer to Rydberg’s analysis from early-August 2015. He identified 34S 94E as being the most likely start point for the flaperon, and made various predictions about where and when debris would arrive onshore elsewhere. Rydberg indicated that a crash location as far south as the ATSB priority search zone was unlikely to have resulted in the flaperon reaching La Réunion; that much more debris would be expected to arrive on shorelines in the western Indian Ocean (and, indeed, another four fragments of MH370 have so far been found); and that comparatively small numbers of debris items should be expected to reach the WA coast, the likelihoods of washing up across the other side of the Indian Ocean being far higher.

The discovery of (so far) a number of MH370-derived debris items on coastlines in the western Indian Ocean but none at all on the shores of Australia therefore present a situation that is consistent with the crash location of MH370 having been further north than the area where the underwater search has been focussed, with 34S 94E being the ‘best bet’ based on analyses using the Adrift model.

 

Consideration of a Controlled Ditch Scenario for MH370

Consideration of a Controlled Ditch
Scenario for MH370

Yap Fook Fah
2016 April 14

 

According to the Inmarsat data, there are two plausible scenarios for the terminal phase of the MH370 flight after a Final Major Turn (FMT) and about another six hours of flight southwards. For ease of reference, I will refer to these as being the Uncontrolled Dive (UD) scenario, and the Controlled Ditch (CD) scenario.

The Uncontrolled Dive Scenario
This assumes a lack of human intervention and that the fate of the aircraft was left solely to the working of its machinery. The definition of the priority zone for the undersea sonar search currently in progress is partly based on this scenario.

The location along the 7th arc has been defined and prioritized by a consideration of: (i) The so-called Constrained Autopilot Dynamics, and (ii) Data Error Optimization (Figure 1). The former assumes that the plane flew by some well-known autopilot mode, while the latter ranked potential flight paths according to how well they fit the Inmarsat data, without regard to how the flight might have been executed.

YFF_Fig1

Figure 1: Representation of the probability distribution at the 0011 arc for constrained autopilot dynamics (red) and data error optimization (green). [1] 

As regards the width of the search zone transverse to the arc, until recently this was defined by an assumption that the plane flew until fuel exhaustion, and, with no one at the controls, fell rapidly from the sky into the Southern Indian Ocean. The width has recently been increased to 60 nm from the 7th arc, to account for the possibility of a glide or controlled ditch.

The UD scenario has been considered the most likely because it fits the Inmarsat data by making the fewest and simplest assumptions. However, it offers no insight into the particular choice of probable flight paths and end zone, except that they are the most consistent with autopilot flight modes and Inmarsat data. Another issue that is becoming increasingly problematic for this scenario is that the undersea sonar search has not been fruitful so far since it started in October 2014.

The Controlled Ditch Scenario
In this scenario, there was someone at the controls right until the end, culminating in a controlled ditch (CD) into the sea. Naturally, a CD scenario begs the question of who was behind the controls, and the reason for his/her action. This study does not examine the “who” or the “why” of such a CD scenario. Personally, I do not think any of the pilots was responsible as I know of no evidence whatsoever that implicates them. Let us just term the person behind the act the ‘perpetrator’.

The scope of this study, therefore, is limited to a consideration of the “what” and the “how” of a CD scenario; that is:

  • How would the position and length of the priority search zone along the 7th arc be different from that of the UD scenario?
  • How would the width of the search zone be different?
  • Given that a perpetrator did a CD, what can we deduce about the nature of the end-game flight path?
  • The recent debris finds (see the report here) imply that there was a large amount of surface/floating debris; therefore we ask how much of the potential CD areas were covered by the aerial search soon after the loss of MH370, and how much has been covered by the ongoing undersea search?

It is not immediately obvious that the hotspot defined for the current search, as well as the spread of the search zone along the 7th arc, would remain the same if the CD scenario were adopted as an assumption, rather than the UD scenario. A CD scenario implies the presence of a perpetrator controlling the final leg of the flight, and this might alter the probability distribution for the search zone because it lends more weight to certain flight modes than others.

Table 1 lays out some of the implications that could be deduced from assuming a CD.

 

 

 

 

Controlled Ditch

which further
1 implies that there was a perpetrator at the controls, implies that the perpetrator wanted to minimize the force of the final impact.
2 implies that perpetrator wanted to minimize debris, implies that number of debris found might be small, mainly exterior parts.
3 implies that action was premeditated, with an intention to make the plane vanish without trace, implies that flight route was carefully planned to avoid detection as much as possible.
4 requires that ocean surface was visible at time of ditching, implies that end point was in a daylight region.

Table 1: Implications of a Controlled Ditch scenario

 

Assuming that a CD implies an intention to make the plane vanish without any trace, Table 2 lays out some of the constraints on the end-game flight path.

 

Avoiding detection during flight and hiding the plane

1 requires that the plane flew to some remote ocean area for ditching.
2 requires that plane flew under cover of darkness to avoid satellite detection.
3 requires that plane flew to fuel exhaustion to minimize risk of explosion on impact and oil leak after crash.
4 requires that the end point is in daylight region shortly before arrival, so that the ocean surface was visible at time of ditching.
5 requires that plane flew a precise end-game path, controlled by autopilot, until the time to ditch at target area.

Table 2: Plausible constraints on the flight path. 

It is also reasonable to assume that the perpetrator did not know that the Inmarsat pings could be used to track the flight, and so the end-game flight path would just be a simple, straight path controlled by autopilot that would achieve the objectives of Table 2. Referring to Figure 1, such a path would be in the Constrained Autopilot Dynamics zone with probability distribution shown in red. In contrast, the Data Error Optimization zone (in green) would be given much less weight as they pertain to more unusual, curved paths.

The first deduction from this study, therefore, is that the CD zone (i.e. where the aircraft is more likely to have ended its flight under the CD scenario) is weighted more toward the southern end of the arc, between 35S and 39S.

Nature of the southern flight path
From the point of view of the perpetrator, a feasible approach to determining a flight path for the CD scenario involves the following steps.

Step 1: Determine the amount of fuel remaining before the FMT at around 1830 UTC, and estimate the time to fly to fuel exhaustion.

Step 2: Work out the sunrise line at, say, 15 minutes before fuel exhaustion. For example, if fuel exhaustion is estimated to be at 00:10 UTC on 2014 March 08, then at this time the plane should reach a location that has a sunrise 15 minutes earlier, i.e. at 23:55 UTC March 7. The pink line shown in Figure 2 are locations that have an apparent sunrise at this time.

 

YFF_Fig2

Figure 2: Sunrise line at 23:55 UTC on 2014 March 7. 

Step 3: Work out the aircraft performance boundary; for example, see Figure 3 below.

 

YFF_Fig3

Figure 3: Aircraft performance boundary for MH370 [2]. 

 

Step 4: The location to aim for is then the intersection between the sunrise line (Step 2) and the fuel performance boundary (Step 3).

It might not be straightforward to work out Step 3 precisely, as the performance boundary depends not only on the amount of fuel, but also the initial position, flight altitude and flight mode. Certainly this would be difficult to work out quickly.

There is, however, a much easier way which does not require Steps 3 and 4 at all. If the plane were to fly along the sunrise line determined in Step 2, then it could be sure to reach the fuel exhaustion point at precisely 15 minutes (or whatever pre-determined time interval) after sunrise.

In Figure 4, the sunrise line for 23:55 March 7, shown in pink, is overlaid with one of the best-fit autopilot flight paths worked out from the Inmarsat data (in white, 186.7 degree rhumb line). The flight path crosses the 7th arc (in red) within the hotspot at (37.6S, 89.0E). It is a notable coincidence that the sunrise line is almost collinear with that modelled flight path.

Note that the sunrise line also crosses the position (30S 90E). These could be a simple set of coordinates to enter into the Flight Management System (FMS) as a target waypoint (as discussed in a previous post on this website).

 

YFF_Fig4

Figure 4: Sunrise line (pink) at 2355 UTC March 7 2014 overlaid with a rhumb line flight path (white) that crosses the hotpot on the 7th arc.

An animation that shows the sunrise effect as the end-game flight progressed can be obtained here. The yellow pin marks the position of the plane as it crosses the seven ping rings successively.

Extent of Controlled Ditch
The recent debris finds, if confirmed to be from MH370, are invaluable because we could at least conclude that (i) the plane flew to the Indian Ocean, and (ii) the plane broke up on impact with the sea, whether in an uncontrolled dive or a controlled ditch. Further, the type, size and condition of the debris might further inform on the likely mode of impact. So, given that there would be surface debris even in the event of a CD, I wanted to use the approach described here [3] to check if potential CD areas have been covered by aerial and/or undersea search.

The method applied was as follows. First, I selected a straight flight path as shown above that matches the BTOs and BFOs. Next, I extended the path for another 100 nm along the same rhumb line, assuming that the plane continued to a CD sometime after 00:19 UTC. The reason for the choice of 100 nm comes from [4], where the following text appears:

Glide area
A simulation was performed to determine the glide distance of the aircraft under active control to maintain wings-level attitude. The simulation (from FL330) resulted in the aircraft gliding for a total distance of approximately 125 NM from the point of the second engine flame-out. 

In order to make this distance the aircraft would travel approximately 15 NM in the first 2 minutes of the descent (approximate time required to start the APU and initiate the log-on sequence). Therefore, from the 7th arc, the aircraft has the potential to glide around 110 NM. Due to the initial direction of travel and the wind conditions on the day, around 100 NM is a more realistic value.

The above results in Google Earth screenshots as shown in Figures 5 and 6. The aerial and undersea search areas are overlaid on the map and the daylight effect for 00:19 UTC March 08 2014 has been turned on (in Fig 5). The apparent sunrise time at 37.6S, 89.0E is 23:55 UTC Mar 07 2014 (i.e. a time stated previously above).

A second path has also been drawn in these graphics where, after reaching (30S, 90E), the plane headed directly south along 90E and flew for up to 100 nm after crossing the 7th arc.

 

YFF_Fig5

Figure 5: Modelled glide paths in the terminal phase. 

 

YFF_Fig6

Figure 6: Zoomed in, with the solar lighting effect turned off to ease viewing. 

Observations

  1. Most potential CD end points lie within the aerial or the already-scanned undersea search zones.
  2. Only a relatively small region of potential CD end points, centred around the path along 90E, would yield debris that would have drifted outside of the aerial search zone (i.e. to the northeast of the indicated end point at 90E in Figure 6).
  3. CD end points that extend to the west of 37.6S, 89.0E on the 7th arc also lie within the aerial search zone. Further, the lack of sunlight would make visibility more difficult for any controlled ditching in this area (i.e. this far west).
  4. CD end points to the east of 90E lie outside of the aerial search zone. However, such end points might require (i) a curved path, or (ii) a straight path with some loitering around 18:25 UTC, or (iii) navigation with a set of more complex waypoints, and (iv) a longer period of exposure to daylight during the flight.

Conclusions

  1. A controlled ditch would go some way toward explaining the nature of the end-game flight path, one that was designed to be flown by autopilot under cover of darkness, and emerge into sunlight at fuel exhaustion for a controlled ditch in the Southern Indian Ocean.
  2. The length of the potential CD area spans a shorter range of longitude than the current search zone, as it is constrained by the level of sunlight and simple, straight, autopilot flight paths. It could be further limited to areas that were not covered by the aerial search in the weeks after the crash.
  3. If a CD did happen, the potential end point would appear to lie in a smaller region than initially expected: see the pink area in Figure 7.

 

YFF_Fig7

Figure 7: Potential CD area in pink. 

4. If the current underwater search does not find MH370 wreckage by June 2016, it does not mean that the effort has been futile and that the Inmarsat data have been invalidated. It could simply be that the assumption of a steep dive at the end (the Uncontrolled Dive scenario) was wrong. The final resting place of MH370 could lie just a little further south.

To reiterate, the intent of the analysis in this report is not to argue that a controlled ditch certainly did occur, nor to suggest any specific person or motivation was responsible if this is actually what occurred. The intent is limited to exploring the implications of such an event (a flight culminating in a controlled ditch) having occurred in terms of what this might mean for the final location of MH370 referenced against the priority underwater search zone, and also the surface areas covered in the airborne search for floating wreckage in March and April 2014.

 

References 

[1] MH370 – Flight Path Analysis Update, ATSB, 08 October 2014; see Figure 5.

[2] MH370 – Definition of Underwater Search Areas, ATSB, 26 June 2014; ; see Figure20.

[3] Was The MH370 Floating Debris Field Detected From Orbit? Duncan Steel, 23 March 2016

[4] MH370 – Definition of Underwater Search Areas, update, ATSB, 03 December 2015; see page 14.

 

The Routes Taken by Floating Debris from MH370

The Routes Taken by
Floating Debris from MH370

Richard Godfrey
2016 April 2nd

(Please see also the addenda at the end of this post, including that inserted on April 4th in which the Rodrigues fragment is identified in terms of which part of the cabin it comprised.) 

 
Preamble by Duncan Steel: 
Since I received the following material for posting from Richard Godfrey about 23 hours ago, a further piece of MH370 has apparently been found on the island of Rodrigues. Independent Group (IG) member Don Thompson has been central in identifying this as likely being a piece from the passenger cabin interior: see this early story in the media.
Before saying more on the significance of that, I might quote from the previous post by Richard, in which was written: “The next most likely destinations are Mozambique, Rodrigues, Mauritius…” One of the hallmarks of a viable scientific hypothesis is its ability to make predictions that are borne out by future observations or measurements.
My immediate response to the Rodrigues item is that, assuming that it is indeed from MH370, it provides another vital indication of the end-of-flight circumstances which could and should inform the ocean bottom search for the wreckage of MH370 and thus the flight recorders. The important thing here is that this is from the interior of the aircraft. The previous four fragments found were parts of the exterior. So long as only exterior fragments had been found, it was still possible to imagine that the aircraft had undergone a controlled ditching in the ocean, based on the idea that those pieces had been ripped off as the aircraft glided down onto the sea surface. The discovery of an interior cabin part indicates rather strongly that the aircraft disintegrated on arriving in the sea: it was a high-speed, uncontrolled crash, as has been argued many times on this website, for many reasons (e.g. the final BFO values are indicative of a very rapid, accelerating descent).
Richard’s analysis of the oceanic drift of floating debris from MH370, based on the model available on the Adrift website (to which another tip of the hat is due), has a wide variety of outcomes in terms of general understandings. An important one is this: the probabilities derived for arriving at the various locations in the western Indian Ocean where MH370 debris has been found may be inverted so as to derive an estimate of how many individual fragments were left floating on the ocean after the crash. The answer is: upwards of 10,000. In itself that number indicates that the final demise of MH370 was a highly-energetic crash.
From the perspective of the underwater search for the wreckage of MH370 there are two important points to be made, to the general reader of this post but most importantly to the people leading the official search program:
(1) There must have been a vast field of floating debris from the crash, which dispersed over following weeks: if it was not seen from the surface-search aircraft then it seems very likely that the crash must have been in a location not covered by those aircraft; the obvious implication of this is: the ocean bottom search should be directed towards areas close to the 7th arc that were not covered by the airborne search (so, see this post and this post).
(2) Whilst there was a large number of floating objects produced in the crash, there was surely also a large number of non-floating objects! That is, at the crash location there must have been many thousands of fragments with densities greater than unity, which sank immediately (unlike, say, suitcases which might take a while to become waterlogged and then sink elsewhere). The implication is that the debris field on the ocean bottom will be spread over some substantial area, dependent on various things such as the depth of the ocean at that location, rather than being a single point or restricted area where the aircraft sank largely intact. Clearly, it didn’t.
The important argument I wish to make here is that the swathes being scanned across the ocean bottom could be quite widely spaced, with spaces left between them to be covered later if required. It’s not necessary – indeed it is counter-productive – to have scan swathes that abut each other.
Before I pass the text over to Richard, here is a matter disconnected from the above, but referring to his post below. Richard has considered various mechanisms that might explain why the flaperon found on La Réunion was encrusted with many goose barnacles, whereas the three debris items discovered on the coast of Africa appeared to be bare of marine growths. One point he did not mention is this: that the ability of those three items to float and so reach the destinations where they were found may have been conditional upon them not being weighed down with barnacles. It might be the the flaperon had an average density (we still await public disclosure of the results of the tests conducted by the French authorities) low enough such that it could continue to float on the ocean despite its crustacean passengers, whereas the smaller items found in Mozambique and South Africa has densities only just less than one gram per cubic centimetre, such that any barnacles would have sunk them.
Finally I note that the initial photographs of the item found on Rodrigues indicate that it was carrying many barnacles.

Introduction 
At the time of writing [DS: that was on March 31st/April 1st], there have been four finds of floating debris items that have either been confirmed or are considered highly-likely to be from MH370 (i.e. the Boeing 7772H6ER aircraft registered as 9M-MRO), as listed in the table below. It may be anticipated that more discoveries of fragments of the aircraft will be made in coming months, spread over the shores of the western Indian Ocean and eventually elsewhere.
MH370_first_four_fragments
In two recent posts (linked here and here) I have described my investigations of the dispersal by ocean currents of floating fragments from assumed crash locations in the eastern Indian Ocean, close to the 7th arc and between latitudes of 30S and 38S, and indicated both (i) where such items are more likely to wash ashore in the western Indian Ocean, and also (ii) the most likely origination (i.e. crash) locations between the above assumed limits. Such drift analyses should be regarded as being statistically-indicative, but by no means definitive: it is simply infeasible to trace the chaotic drift of specific items either in the forward- or backward-directions.
The first find (the flaperon discovered on La Réunion) carried a large and obvious population of barnacles, whereas the other three finds in the table above display a puzzling lack of evidence of marine life in publicly-available photographs; note, though, that examination and species identification has not yet been completed or published.
One possible explanation for this obvious difference between the flaperon and the other items might be linked to the differing routes taken by the floating debris, and this is a matter which I address in the present report.
There are warmer and there are colder ocean currents. There are variations in the nutrients in different ocean areas that are required to support different types of marine life. How might such considerations affect the growth of barnacles and other organisms on the floating debris?
Methodology
The Indian Ocean South Equatorial Current drives floating debris generally westwards towards Africa. Madagascar, with a total coast line length of 4,828 km, then forces a divide of that broad current around its northern and southern tips. Whilst the currents are seasonally-variable, there are many maps available on the internet which indicate the divide being discussed herein, such as that shown below, or this one.
RG_currents_1
General map of Indian Ocean currents, with the 7th arc between 30S and 38S broadly indicated in dark blue and the first four debris finds (locations as listed in the table above) marked in red. 
According to the Adrift model, 28 per cent more floating debris (i.e. a 56/44 split) would travel via the northern tip of Madagascar, for items originating between 30S and 38S on the 7th arc (see my previous post for more information). The highest drift probabilities around both the northern and southern tips of Madagascar, are just off the coast rather than further offshore, as one might imagine. The time taken to reach the northern and southern tips of Madagascar ranges between 12 and 16 months (from the starting locations as given above).
I downloaded forward-drift data from the Adrift website for both the northern tip of Madagascar at 12S 49E and the southern tip at 26S 46E for the months of January, March, May, July, September and November. As aforementioned, there are significant seasonal changes during the year.
Although the shortest routes to the Paindane (Mozambique), Paluma (Mozambique) and Mossel Beach (South Africa) debris finds are all from the southern tip of Madagascar, it happens that all three locations could be reached by the drift patterns via either northern or southern tips of the island. That is, the fragments could have taken routes either north of the island and down through the Mozambique Channel (perhaps joining the Agulhas Current), or else passing south of the island. But which is the more likely, in each case?
Results
The Paluma find is 1.5 times more likely to have arrived via the northern route; that route is also a much better fit to the time of discovery (end of February).
The Paindane item is 33 times more likely to have arrives via the southern route; that route is also a better fit to the time of discovery (end of December).
The Mossel Bay fragment is 3.7 times more likely to have arrived via the southern route; that route is also a better fit to the time of discovery (mid-March).

As a general statement (for these and likely — based on the drift modelling — many impending discoveries) it is conceivable that times of landfall and times of discovery may be separated by some months, especially in remote areas. In the four cases in the table above, however, it appears that the areas were regularly visited, so that the discoveries were made quite promptly after the items washed ashore.

It is also conceivable, even likely, that floating items might make landfall but return to the sea, perhaps washing up again in much the same location, or some distance away. The Adrift model incorporates such a feature (that is, floating objects are assumed to be reflected rather than absorbed by a shoreline).
Discussion 
 
(1) Implications of Indian Ocean sea surface temperatures 
The ATSB has pointed out that a southern drift route generally occupies cooler waters than a northern route, and of course that is generally the case for routes south of the equator.
The graphic below comprises an overview of Indian Ocean sea surface temperature for each month of the year (thanks, Barry Martin).
 Indian_Ocean_monthly_temperatures
Indian Ocean sea surface temperatures for each month of the year. 
It would appear obvious that both a northern drift route to 12S 49E (i.e. the northern tip of Madagascar) and a southern route to 26S 46E (i.e. the southern tip) must spend significant time above latitude 30S, where barnacles apparently start to grow, although a path passing close by the southern tip might avoid spending much time to the north of 30S.
The three fragments found on the African coast 
If floating debris took a path passing slightly further south of Madagascar then it could remain in colder waters (especially between July and October) below 30S, under which circumstance barnacle attachment and growth is contra-indicated. Thus it might be that the three items found on the coast of Africa reached their destinations via such more-southerly routes. Let us examine each in turn.
The Paluma item (‘NO STEP’) that arrived at around 22S might have been expected to show evidence marine life, because it most likely (from the drift modelling) followed a northern route in warmer waters; on the other hand, if no marine life attachments are/were identified, this might be interpreted as evidence that it took the southern route. (From the preceding discussion: 1.5 times more likely to have followed the northern route based on the drift modelling, and therefore a 40 per cent chance that it took the southern path.)
The Paindane item (‘676EB’) discovered at around 24S may well show some evidence of marine life, even though it most probably arrived via the southern route past Madagascar, mainly occupying cooler waters.
The Mossel Bay find (‘Rolls Royce’) might not be expected to show evidence of marine life because it was discovered at around 34S and may well have spent most of its ocean transport time in the cooler waters below 30S.
Modelled route of the flaperon to La Réunion 
Contrasting with the above three items, the flaperon found in La Réunion at 21S carried many barnacles. Its estimated track is as below, based on an assumption that it started from close to the 7th arc between 34S and 37S.

Flaperon_drift

As can be seen, such a route would lead to the flaperon spending most of its drift time above 30S, thus perhaps enabling the substantial barnacle growth witnessed.

(2) Implications of Indian Ocean chlorophyll concentrations
At the base of the ocean food chain are single-celled algae and other plant-like organisms known as phytoplankton. Like plants on land, phytoplankton use chlorophyll and other light-harvesting pigments to facilitate photosynthesis. Where phytoplankton grow depends on the available sunlight, temperature, and nutrient levels. Because cold waters generally contain more nutrients than warm waters, phytoplankton tend to be more plentiful where the sea is cooler.
Marine growth (e.g. barnacles) on floating items is dependent upon the availability of their respective nutrients in the water, in this case the phytoplankton. Thus if phytoplankton concentrations are low, one may expect barnacle growth to be limited.
Measured chlorophyll concentrations may be interpreted as being indicators of phytoplankton levels. In the Indian Ocean the chlorophyll concentration varies considerably, for example due to the prevailing winds and other seasonal effects. In general, coastal regions (due to run-off nutrients) and colder waters (due to upwelling nutrients) are higher in chlorophyll concentrations.
In the following maps the chlorophyll concentrations are shown, scaled from purple/blue representing the lowest to yellow/red the highest, for the months May-June and September-October.
Indian Ocean chlorophyll May-Jun
Indian Ocean chlorophyll Sep-Oct

Although it appears likely that the floating debris from MH370 was carried westwards towards Africa by the Indian Ocean South Equatorial Current through warm waters (i.e. where barnacle attachment and growth is feasible), these waters have relatively low concentrations of chlorophyll in the maps above, and therefore limited amounts of phytoplankton, and this militates against substantial barnacle growth.

As floating debris spends time in coastal regions, higher concentrations of chlorophyll/phytoplankton and hence macroscopic marine life are experienced. One possibility, therefore, is that the flaperon found in La Réunion spent some time near the coast before landfall, whereas the coastal Africa finds beached as soon as they arrived.

Addendum from Richard Godfrey: The discovery of a fragment of the interior of MH370 on the island of Rodrigues, as discussed by Duncan in his preamble above, means that the list of debris finds should now be expanded, as below:
Debris Finds

Addendum from Don Thompson: An alternative reason for the Réunion and Rodrigues items being barnacle-encrusted but not the other three might be as follows. The lepas (goose barnacle) colonisation may be a feature of proximity to coastlines inhabited by lepas colonies. Therefore, debris ‘dropped’ into a mid-ocean region (i.e. the crash site) might be expected to be ‘clean’ of lepas barnacles until free-swimming barnacle nauplii, released from reproducing coastal colonies, are encountered. That would fit with Réunion and Rodrigues, contrary to the sandy-shored arrival locations of the other items so far discovered.  Colonisation of 9M-MRO debris by barnacles should generally be expected to be sparse.

Addendum April 4th, from Don Thompson:  With respect to the fragment of the aircraft found on the beach in Rodrigues, it appears that Annette in Australia has identified rather precisely which part of the cabin it came from; see the edited and marked-up photograph here. One might watch, also, the final ten seconds of this YouTube video.

Space Scientist, Author & Broadcaster