MH370 Search Area Recommendation

MH370 Search Area Recommendation

The Independent Group
September 9, 2014

1 Executive Summary 
Shortly after the disappearance of MH370 on March 8th, an informal group of people with diverse technical skills and backgrounds came together on-line to discuss the event and analyse the technical information that had been released. The group has since become known as the “Independent Group”, or “IG”. The IG has continued to share an extensive array of reference material and their experience with aircraft, satellite, radar, and meteorological systems. Several high fidelity flight path models have been independently developed, refined and compared. These models now incorporate state-of-the-art satellite geometry and physics. They make use of the available radar,
ADS-B, BTO, BFO, magnetic declination and meteorological data, as well as the operational and practical knowledge contributed by experienced, current B777 pilots.

In a statement released June 17, 2014, the IG recommended that the search area be defined based on an estimated 6th arc location of 36.0S, 88.6E. At that time, the 00:19 “partial ping data” was not well
understood, nor did the BTO and BFO models reflect the information disclosed in the ATSB Report AE-2014-054. However, with new information in hand, as well as confidence in the 7th arc data, we have revised the estimate to a likely point of impact close to 37.5 S, 89.2 E.


Figure 1: Results for 4 independent models assuming a nominal cruise altitude and speed. Green line is the 7th arc and the brown line is the estimated fuel exhaustion circle given in the ATSB report. 

2 New Information and Developments

2.1 ATSB Report AE-2014-054
The ATSB Report AE-2014-054, first released June 26, 2014 and revised August 18, 2014, contained valuable new data and analysis. It also provided insight into the methodology used by the ATSB for the selection of the Underwater Search Areas. This document answered many questions about the crucial metadata missing from the Inmarsat Signaling Unit Log for MH370, released May 26, 2014.

In particular, the revised definition of the BFO values made possible more accurate use of the BFO data. We have independently simulated the EAFC residual errors assuming the geographic location of the Perth GES is 31° North and the results match the trend of the data in Table 4. However, the match is not perfect,
leaving some doubt about the accuracy of the measured values in Table 4. We therefore urge Inmarsat to disclose further details of the configuration of the Perth EAFC, firmware version and the specific details of how the values in Table 4 were measured or computed.

2.2 Turn to the south; 1840 BFO data analysis
Based on recent news reports, it appears that ATSB is now incorporating the BFO data available at 18:39/18:40, as recommended by the IG in our July 17, 2014 Update. We reiterate our opinion that MH370 was probably headed generally to the south at that time.

2.3 7th Arc BFO Data Analysis
We agree with the ATSB that MH370 impacted the water very near the 7th arc. We also agree with the assessment that the second engine reached fuel exhaustion approximately 03:40 minutes before the 00:19:29 logon. Given that the autopilot would have disengaged at approximately 00:15:49, the BFO values at 00:19:29 and 00:19:37 indicate that the aircraft was already in a spiral dive at 00:19:29. We estimate the Rate of Climb (ROC) was approximately -15,000 ft/min at 00:19:37 and accelerating at approximately 22 ft/sec2. Thus, we believe MH370 impacted the water within seconds after the last signaling unit log record, and within 1 NM of the 7th arc. This finding suggests that the width of the impact arc could be reduced from -20/+30 NM to approximately ±10 NM.

2.4 Aircraft Performance Limitation
The ATSB Report provided an estimate of the maximum range based on available fuel as of 17:07 (reported in an ACARS message) and the PDA numbers for the 2 engines. The details were not provided, but Figure 20 on page 22 provided a graphical estimate of the range data. We now acknowledge that the performance range limit data is potentially of greater value than previously understood. We note that the southern intersection of the 7th arc and range limit coincides with the IG model results for the nominal case. If the range estimates are accurate, then the most likely impact areas would be close to the northern or southern limits, not the center of the arc.

2.5 Refined BFO Model
We have refined and updated the BFO model in our path models to use the BFO definition provided in the ATSB Report at Page 55. We believe the BFO bias is approximately 153.7 Hz based on calibration at Gate C1 and the available ADS-B data in the early part of the flight. To estimate the BFO values at times other than those listed in Table 4, we have developed a sinusoidal function that fits the values in Table 4 for those times in which the satellite was not eclipsed, and then added back the effect of the eclipse. This model produces values in close agreement with the values in Table 4.

2.6 NOAA Wind and Temperature Fields
We have incorporated data from NOAA wind and temperature fields to estimate TAS and ground speed.

2.7 B777 Pilot Interviews
We have conducted interviews with several B777 pilots and incorporated their experience, especially with respect to system configurations pilots would typically use.

3 Applying Human Factors to the Analysis

The ATSB analysis used two basic analysis techniques referred to as “Data Driven” and “Flight path/mode driven” (page 18). While we agree that these statistical methods are reasonable techniques, both tend to overlook or minimize likely human factors in favor of pure mathematical statistics. This ATSB approach appears to have resulted in a conclusion that the most likely average speed was approximately 400 kts (Appendix A). However, 400 kts is not consistent with standard operating procedure (typically 35,000 feet and 470-480 kts), nor is it consistent with the likely speed a pilot would choose in a decompression scenario (10,000 feet and 250-300 kts). A speed of 400 kts may minimize the BTO and BFO errors for a given set of assumptions, but the errors can also be shown to be very small for other speeds. Given all the tolerances and uncertainties, we believe it is important to consider human
factors with more weight.

3.1 Normal Cruise Scenario
B777 pilots consistently tell us that under normal conditions, the preferred cruise attitude would be 35,000 feet and the TAS would be approximately 470-480 kts. We believe this is the most likely case for MH370, and note that the last ADS-B data available indicated that MH370 was at 35,000 feet and 471 kts at that time.

Although few primary radar data details have been released, the data from 18:02 to 18:22 is believed to be more consistent with this normal speed range than an assumed 400 kts. We note that the Normal Cruise Scenario produces a path that matches the southern fuel limit at the 7th arc, making this the most likely scenario.

3.2 Decompression Scenario
If the aircraft experienced a decompression event around IGARI, B777 pilots tell us the standard operating procedure would be to turn to the nearest available airport and descend rapidly to 10,000 feet. Depending on the weight of the aircraft (mainly fuel on board), the TAS would be set to 250-300 kts. MH370 did make a turn and headed back towards land and several possible intended airports. However, the limited radar data released so far does not seem to be consistent with this lower speed range. Nevertheless, if MH370 did experience a decompression event, and did descend to 10,000 feet at some point, the speed would have been necessarily reduced to approximately 300 kts. We note that using a TAS assumption of approximately 323 kts, the path terminates on the 7th arc near the northern intersection of the fuel limit, making this another case consistent with the fuel/performance limit. The BFO errors are somewhat larger for this case compared to the Normal Cruise Scenario, but still within reason.


Figure 2: Paths for Normal and Decompression Scenarios. Note that both paths intersect the performance limits where the 7th arc and the fuel circle intersect.

3.3 ATSB 400 kts Scenario
ATSB considered thousands of paths, with many possible speeds tested. However, the most likely scenario chosen by ATSB (low BTO and BFO errors) had a TAS of 400 kts. But ATSB provides no rationale for a pilot to have made a deliberate selection of this speed. If the aircraft was flying under the control of the autopilot, a human must have selected the configuration. We doubt that a pilot would select 400 kts, and a lower altitude to match, regardless of the motivation. Using our path models, we have confirmed that the path would end on the 7th arc in the ATSB Priority Search Area if the speed was 400 kts, but we note that this result is the least consistent with (a) the most likely speeds a human would choose and (b) the fuel range/performance intersections with the 7th arc.

4 IG Analysis
The assumptions common to the models used by our group for the Normal Cruise Scenario are level flight at FL350 at normal cruising Mach numbers with AFDS LNAV/VNAV roll and pitch modes engaged. In most cases, we assume a small, gradual reduction in TAS as the fuel is burned off. We have constrained the path solutions so that only one major turn occurs between 18:28 and 18:39. We assume a track of about 300°T turning south to about 186°T. Candidate solution paths generate BFOs within 5 Hz, are within 50 km over the earth’s surface of each ping ring from 19:41 onwards and have endpoints on the 7th ping ring clustered around 37.5 S, 89.2 E.

5 Recommendations
1. We recommend that the Priority Search Area be moved further south from the present location. The most likely point of impact is near the intersection of the 7th arc, the fuel exhaustion circle
and the path model end points given in Figure 1 above, and Figure 3 below.
2. The width of the Priority Search Area can be reduced to approximately ±10 NM, thereby allowing for the length of the search area arc to be increased for a fixed budget of 60,000 km2.


Figure 3: Illustration of Search Areas corresponding to the three scenarios described in Section 3. (Search area dimensions are not to scale.) 

6 Independent Group
The following individuals have agreed to be publicly identified with this statement, to represent the larger collective that has contributed to this work, and to make themselves available to assist with the investigation in any constructive way. Other members prefer to remain anonymous, but their contributions are gratefully acknowledged.

Brian Anderson, BE: Havelock North, New Zealand
Sid Bennett, MEE: Chicago, Illinois, USA
Curon Davies, MA: Swansea, UK
Michael Exner, MEE: Colorado, USA
Tim Farrar, PhD: Menlo Park, California, USA
Richard Godfrey, BSc: Frankfurt, Germany
Bill Holland, BSEE: Cary, North Carolina, USA
Geoff Hyman, MSc: London, UK
Victor Iannello, ScD: Roanoke, Virginia, USA
Barry Martin, CPL: London, UK
Duncan Steel, PhD: Wellington, New Zealand
Don Thompson: Belfast, Northern Ireland
Jeffrey James Wise, BS: New York, NY, USA

Appendix A: Links to detailed Flight Models 

First model  (736 kB spreadsheet)
Second model (21.1 MB spreadsheet)
Third model  (20.4 MB spreadsheet)


A six-page PDF containing the above report can be downloaded from here or here


Further Statement from an Independent MH370 Investigation Team

Further Statement from an Independent MH370 Investigation Team

We have refined our analysis models over a period of time and have found no meaningful error in the assumptions or computational approaches that we have taken. We remain concerned that some information of importance may have been withheld for reasons that have not been made public. This has limited the scope of our analysis to exploration of a number of flight dynamics models and technical scenarios that appear to be simple and plausible. Recently we have attempted to confirm the selection of the current search area without presuming a specific set of events other than being consistent with the disclosed satellite data, radar data, and the aircraft technical performance characteristics.

We reiterate that our original proposed search area centred on 36.0S 88.5E has a higher probability of a successful search result than the presently envisaged official search area.

Endpoints near the final arc starting from about 39.7S 84.4E and moving along the ping arc to about 27.5S 99.9E can be computed using the same data set as we have used, depending on  hypothesized flight path scenarios (e.g., very low effective ground speed, or manoeuvring) during the interval between the satellite data obtained at 18:40 UTC and 19:41 UTC. However, unless further information becomes available, we consider such scenarios to be too speculative to pursue as a group.

Brian Anderson, BE: Havelock North, New Zealand
Sid Bennett, MEE: Chicago, Illinois, USA
Curon Davies, MA: Swansea, UK
Michael Exner, MEE: Colorado, USA
Tim Farrar, PhD: Menlo Park, California, USA
Richard Godfrey, BSc: Frankfurt, Germany
Bill Holland, BSEE: Cary, North Carolina, USA
Geoff Hyman, MSc: London, UK
Victor Iannello, ScD: Roanoke, Virginia, USA
Barry Martin, CPL (EASA-FCL Commercial Pilot Licence): London, UK
Duncan Steel, PhD: Wellington, New Zealand
Don Thompson: Belfast, Northern Ireland
Jeffrey James Wise, BS: New York, NY, USA


Previous statements from this team can be found here and here; these contain background material plus a variety of questions, many of which are yet to be answered.

This is not necessarily the final word on MH370 on this website, but any re-opening of discussions here will await the availability of significant new information.

In amongst the 6,000 comments and replies following the major posts concerning MH370 on this website are many invaluable suggestions and analyses from other able and generous people who have contributed in various ways. Anyone just tuning in: I suggest you look through those, because past experience has shown that the answers to many queries have already been answered therein.

My thanks to all for their interest and kind words – Duncan.


Radar Coverage of the Unknown Parts of the Flight of MH370

Radar Coverage of the Unknown Parts of the Flight of MH370

Duncan Steel, 2014 August 20.

There being a need for a fresh post here from me so as to start a new set of comments and responses from others, the length of the comment section under the previous post now being unwieldy, I turned my mind to what to put into that/this post. The obvious thing to focus on is that part of the flight of MH370 which is most unknown, and controls evaluations of where the aircraft ended up: I refer to its path northwest over the Malacca Strait and then its apparent turn to the south, this being at an indeterminate time after the final publicly-known radar detection at 18:22 UTC. There also being open questions with regard to the radar-tracked path prior to that time, I have now accomplished what I have been intending to do for the past three months: insert into an STK 3D scenario various military and other radars, and examine their potential coverages in the area in question. (I know it was three months ago that I started on this because when I searched for my ‘MH370_radar’ scenario I found that I had last saved it around May 20th; apologies for the delay.)

A set of radar sites was kindly supplied to me by Don Thompson, and others have also been helpful in this regard. Don’s list appears in the table below, and I added hypothetical radars located on Christmas Island and at the Cocos Islands airfield because many times the potential detection of MH370 from those sites as it flew southwards has been suggested.


As always, if any reader finds an error, please let me know. In the case of the final two locations I simply estimated likely coordinates and elevations for the radars.

In none of these cases have I made any attempt to identify and duplicate the functions of any specific radar installation: the only thing I am considering here is the locations of the radars, and their potential coverages as limited by their elevations/heights above the WGS84 ellipsoid at that latitude, and also putative altitudes for the aircraft (limited to four values here: 5,000, 10,000, 20,000 and 35,000 feet). In essence I am thinking about some generic radar (or other sensor) at each location, and asking: how far away might the aircraft be, and yet still be above the horizon so that a line-of-sight is viable?

Note also that I have not (yet) tried entering any topography in order to investigate the limitations on coverage it imposes, although this can be done in STK: this is a level of complexity that I have not yet addressed. Therefore it is distinctly possible, even likely, that in various directions from any particular radar the capability to ‘see’ the aircraft is limited by nearby terrain. For example, I placed the Christmas Island putative radar at the airport there, whereas the hills at the western end of the island would curtail any coverage along an arc at least from due west to southwest.

All I am doing here, then, is defining the furthest distances that a radar might be able to see the aircraft based on the WGS84 shape of the Earth, and the heights above that smooth Earth shape of the radar apparatus and the aircraft. The method I followed is very simple, as below.

Given the radar site’s latitude I calculated the terrestrial radius at that point, which I term R. Let the radar elevation/altitude be h, and the aircraft altitude be H. Assuming that R is constant across the whole of the radar’s coverage, the horizon as seen from the radar is at a distance x given by:

x = sqrt[sqr(R + h) ─ sqr(R)]

Since h is much smaller than R, to a good approximation one can use:

x = sqrt(2 R h)

The straight line from the radar to the horizon can then be extended to an altitude H which is an additional distance y away, where (as above) one can calculate y from:

y = sqrt(2 R H)

The total distance (x + y) then is the maximum possible range at which the aircraft would be above the horizon. These ranges for H = 5,000, 10,000, 20,000 and 35,000 feet are given for each radar site in the table above; all those ranges are given in kilometres.

Please be clear that this does not mean that any or all of the actual radars could or would have detected the aircraft out to those distances: these are simply maximum line-of-sight ranges. The actual radars would be limited by:

(a)    Detectability considerations: the power returned by a target drops off as the fourth power of its distance, and the detectability also depends on such things as the target’s radar cross-section at the wavelength used, aspect effects, the gains of the transmitter and receiver antennas (these have the same value for a monostatic radar), the power transmitted in each pulse, the background noise from natural sources (the cosmos, mostly), local radio noise sources, and so on;

(b)   The signal processing of the returned echoes; and

(c)    The range limits and gating used: obviously if a radar system is programmed to collect echoes only from ranges out to 200 km, it will not identify objects at 250 km.

All I am attempting to do here, then, is to provide some visualisations of the best possible radar coverage that would be feasible, based solely on the locations and elevations/altitudes of these radars.

Here is the coverage of all the radar sites in accord with the above descriptions, as a view of a 3D window in STK:


For each of these coverage rings I have produced KML files, which anyone can download from here and then display in Google Earth or similar tools. There are 52 KML files in total. For each ring there is a ‘wall’ of the appropriate height (i.e. from the surface to the relevant altitude). Although in my STK scenario the rings appear discrete, as above, in Google Earth I have found that the area interior to each ring seems to fill in with the colour of the ring itself. Apologies, but I have as of yet been unable to stop that occurring!

Here is a 2D map of all the 52 coverage rings:


For clarity, and for those wanting a quick look without using the KML files, in the 2D maps that follow I show the coverage rings selected a few at a time.

Thai sites: 


Malaysian sites:


Indonesian sites:


Australian sites: 


Space Scientist, Author & Broadcaster