Some Observations on the Radar Data for MH370

Some Observations on the Radar Data for MH370

by Victor Iannello, ScD,
August 18, 2015

A PDF of this paper is available for download from here (720  kB).

Please note: The views expressed here belong solely to Victor Iannello and do not necessarily represent the collective view of the Independent Group (IG), or any other group or individual. 


Summary

This work analyzes the position and time data derived from the publicly-available radar data for MH370. Some of the findings are:

  • After the turn back towards the Malay Peninsula, the flight path recorded by civilian primary surveillance radar (PSR), civilian secondary surveillance radar (SSR), and military radar are consistent with a flight at a Mach number (M) equal to 0.84 at a cruising level of FL340.
  • If the aircraft did fly at a steady M = 0.84, then the timestamps for some of the PSR contained in the Factual Information (FI) [1] are offset by about 35 s.
  • After the left turn at around 17:23:38 UTC, the aircraft might have descended from FL350 to FL340 and accelerated from a ground speed of 473 kn to a ground speed of greater than 500 kn.
  • In the FI [1], the PSR data between 17:47:02 and 17:52:35 UTC are attributed to the radar site at Kota Bharu, but more likely were collected by another radar site. The PSR data between 17:30:37 and 17:44:52 are correctly attributed to Kota Bharu.
  • In the FI [1], it is stated that Indonesian military radar recorded MH370 as it traveled toward IGARI but not as it traveled back over Malaysia. One explanation is that Indonesian radar site was powered down after midnight, local time.
  • The sharp turn to the left at around 17:23:38 UTC is unexplained, and could be due to either an inaccurate graphical portrayal of the radar track, or crossing radar tracks from two aircraft.
  • The curve in the radar path close to Kota Bharu can be explained by “slant range” due to high altitudes and close distances.
  • Fuel consumption models which assume that MH370 flew near Long Range Cruise (LRC) speeds and at cruising altitudes between 17:07 and 18:22 are likely accurate.

The estimated path for MH370 from takeoff to the last radar point is shown in Figure 1.

 

Introduction

After the SSR data were lost from MH370 at 17:21:13, the only quantitative data that have been publicly disclosed are the PSR data that were collected by the radar head at Kota Bharu Airport, selected military radar data from one or more undisclosed radar sites, and the signaling data from the Inmarsat satellite network. In this work, we take a closer look at the radar data by individually treating the following four segments of the path:

  • The known path northwest over the Malay peninsula ending with the last SSR data point at 17:21:13 just after passing IGARI
  • The change in direction that started at 17:21:13 and ended with the resumption of the PSR data at 17:30:37, as captured by military radar
  • The southwest path over the South China Sea, over Kota Bharu, and ending just south of Penang Island, as attributed in the FI [1] to the PSR data from Kota Bharu
  • The northwest path over the Malacca Strait, as captured by military data

Fig1

Figure 1. Summary of Radar Data

Solution Procedure

After analyzing timestamps, positions, and speeds for individual segments of the flight path, it was decided that the imprecision of the measured data precludes accurately determining the speeds for the individual segments due to the short time intervals and uncertainty in position and time. Instead, we hypothesized that the Mach number and altitude were essentially constant from the time of the left turn until the last radar point in the Malacca Strait, and then we tested whether this hypothesis is consistent with the data that was measured between the first and last data points.

In order to simulate the path of MH370 over the entire interval, an Euler integrator was used. For the segments of the path where there were turns, a time step of 1 s was used, and a 1-min time step was used for straight parts of the flight. The track angle was allowed to vary from time step to time step by imposing turn rates, expressed in units of deg/s. In this way, realistic curvature of the path could be modeled. The speed was adjusted so that two points are pinned in time and space: the left turn at 17:23:38 UTC, and the last radar point at 18:22:12 UTC. By iteratively varying the speed and the turn rates, a match of the flight path was obtained.

In order to properly include the effects of temperature and wind on the calculation, meteorological data were included in the analysis. The meteorological data for March 8, 2014 at 00:00 UTC [2] for a pressure altitude of 34,000 ft (FL340) were extracted from the GDAS archive provided by Barry Martin. This tabulated data has a spatial resolution of 1 deg in latitude and longitude. The wind data were used without alteration, but the temperatures were adjusted by -1.98 K / 1000 ft for altitudes equal to and less than FL360. (The tropopause for the ISA is at FL361.)

It was found that a constant true air speed (TAS) of 498 kn satisfies the time and distance relationship after accounting for wind. At FL350 and the prevailing temperature, this corresponds to M = 0.844. This is a higher speed than recommended for the B700-200ER to achieve Long Range Cruise (LRC) fuel efficiency. On the other hand, TAS = 498 kn corresponds to M = 0.840 at FL340, which is a more typical speed for cruising with a B777-200ER [3]. Therefore, we assume that MH370 likely flew at FL340, which required a descent of about 1000 ft after its last recorded value of FL350. An even cruising level such as FL340 is generally required of westbound flights in Reduced Vertical Separation Minimum (RVSM) airspace, such as within the Kuala Lumpur FIR. At the prevailing conditions on that day, FL340 corresponds to a geometric altitude of about 36,000 ft.

As a rough check of the validity of the tabulated wind and speed data, we can compare it to the data that were measured by the aircraft and included in the ACARS report at 17:06:43 [1]. At FL350, the temperature was 229.4 K and the wind speed was 17 kn from a direction of 70 deg. For the position of the aircraft at this time, the meteorological data predicts a temperature of 229.1 K and a wind speed of 15 kn from a direction of 67 deg. Therefore, the measured and tabulated temperatures match well, and the wind data values are also close.

 

Northwest Path over Malay Peninsula

The path of MH370 out of Kuala Lumpur International Airport (KLIA) and over the Malay Peninsula was captured by PSR and SSR data from the civilian radar site at Kota Bharu, as well as by ACARS data transmitted over the Inmarsat satellite network at 16:41:43, 16:46:43, 16:51:43, 16:56:43, and 17:06:43 UTC. The FI [1] reports that radar data showed that the aircraft passed over IGARI at 17:20:31 UTC, and the last SSR data position was recorded at 17:21:13 UTC, at which time the ground speed was 473 kn.

In order to quantitatively analyze the PSR data from Kota Bharu, the image of the PSR from the FI was positioned and sized on Cartesian coordinates using the waypoints PHUKET, MEDAN, PENANG, IGARI, and MERSING as registration points, where the position of the waypoints could be discerned from the image by the intersection of airways. The result is shown in Figure 2.

As can be seen in Figure 2, the agreement between the PSR (underlying black), SSR (white line), and the ACARS (white circles) data is excellent.

The FI [1] states that the Indonesian ATC in Medan, Sumatra, did not record an SSR transponder signal from MH370. Indonesian military radar did record MH370 as it headed towards IGARI but recorded nothing after the turn back towards Malaysia. As the aircraft left KLIA at around 16:41 UTC and passed IGARI at around 17:21 UTC, it appears that Indonesian radar lost the signal in that time interval, corresponding to 23:41 to 00:21 local time in Sumatra. One possibility is that at midnight, the military radar sites in Sumatra were powered down.

Fig2

Figure 2. Primary Surveillance Radar (PSR) Data

Southwest Path over Malay Peninsula

Also included in Figure 2 is the PSR data from the time it reappears at 17:30:37 UTC to the last point at 17:52:35, for a total time interval of 21 min 58 sec, or 21.9667 min. Over that duration, the PSR data consist of four segments separated by three gaps in the data. From the FI [1], the time at the start and end of each segment is known, and is shown in Figure 2.

Figure 2 shows the calculated path (yellow) for the time interval. The meteorological data indicates that over the interval of the southwest path, there was an average tailwind of 12 kn at the indicated altitude. Therefore, at the true air speed of 498 kn, the average ground speed was around 510 kn.

According to the FI [1], the speed recorded by the military data was between 494 and 529 kn and the “registered” (geometric) altitude was between 31,100 ft and 35,700 ft. These values are not far from the proposed values of 510 kn and 36,000 ft. The deviation is likely due to the inaccuracy in obtaining speed and altitude information from the military radar data.

The times for the start and end of the four segments are shown in Figure 2 for the reconstructed path. In this way, it is possible to compare the position of the aircraft with the radar data at these times. It can be observed that for the first three segments, there is an offset between the radar data (underlying black) and the reconstructed path (yellow). The offset corresponds to about 35 s of flight time. For the fourth segment south of Penang, there is little or no offset. One explanation is that this offset is due to a delay between the time the radar contact was acquired at the radar head in Kota Bharu and when it was stored at the Kuala Lumpur ATC, although the detailed knowledge of how the data are aggregated and stored is not known.

A radar site estimates the distance between the radar head and the aircraft by measuring the round trip time for the transmitted radio signal and relating the time-of-flight to a distance based on the speed of light. As such, the radar is measuring the range between the radar head and the aircraft rather than measuring the distance along the ground. The radar range is sometimes referred to the “slant range” as it represents the hypotenuse of a triangle, where the altitude and the ground distance are the legs. The radar range and the distance will differ when the aircraft is at a distance that becomes comparable to the altitude of the aircraft, in which case a straight path towards and from the radar head will be appear on a radar screen as curved.

The effect of radar slant can be seen in Figure 2 as the aircraft approaches Kota Bharu around 17:34. The solid yellow line represents the reconstructed flight path, and the curved dotted line represents the slant range. The predicted slant range follows the trend of the radar data, as represented by the underlying black line. This suggests that the flight path truly was straight as it passed Kota Bharu.

 

Change in Direction from Northeast to Southwest

The military radar data presented in Figure 2 of the ATSB Report [4] from June 26, 2014, are used to reconstruct the path of MH370 after passing IGARI. The military data from the ATSB report are used as an overlay, and the coast of Malaysia is used for registration of the overlay. The result is shown in Figure 3.

The path is assumed to follow a trajectory towards BITOD at the last recorded ground speed of 473 kn until a sharp turn commences at around 17:22:52. The military data show an impossibly steep turn that would indicate that the graphical representation in the figure is not accurate or the radar data has been misrepresented. It is possible that the sharp radar track is actually crossing radar tracks from two separate aircraft. These hypotheses merit further investigation, and will be the subject of future work.

After the steep turn, the path is reconstructed with the assumption that the plane is flying at M = 0.84 and FL340. For this portion of the flight, this corresponds to a true air speed of 498 kn and a ground speed of 505 kn. The turn represents a rate of about 1 deg/s, which at 498 kn corresponds to a bank angle of about 24.5 deg. This is within the allowable limits of automated flight for a B777.

Fig3

Figure 3. Military Radar Data for Left Turn after IGARI

Northwest Path over the Malacca Strait

On March 21, 2014, officials from Malaysia made a presentation to the next-of-kin at the Lido Hotel in Beijing. Several photographs were taken of slides from this presentation, including a slide presented by a Lieutenant General from the Malaysia Royal Air Force which showed an image of the military radar data over the Malacca Strait [5]. Here, we rely upon the work of Ron Belt [6], who performed an earlier study of the radar data over the Malacca Strait and extracted the radar data from this slide and produced several helpful figures.

In Figure 4, one of the figures from [6] was used as on overlay, where the waypoints VAMPI, MEKAR, PENANG, and LANGKOWI are used for registration. Using a speed of M = 0.84 and a cruising level of FL340, turns were adjusted to match the radar data. The ground speed averages 502 kn over this interval, and the calculated position at 18:22:12 UTC matches the position of the last radar point on airway N571.

Fig4
Figure 4. Radar Data over the Malacca Strait

Conclusion

After MH370’s turn back towards the Malay Peninsula, the flight path recorded by civilian primary surveillance radar (PSR), civilian secondary surveillance radar (SSR), and military radar are consistent with a flight at a Mach number (M) equal to 0.84 at an altitude of FL340. With this assumption, some anomalies that were identified include an impossibly sharp turn to the left after passing IGARI, and timestamp inconsistencies as recorded by the PSR data from Kota Bharu. As MH370 likely flew at efficient cruise speeds and altitudes during the time it was captured by radar, fuel consumption models that assume fuel flow rates based on LRC conditions during this time interval are likely accurate. For instance, at FL350 and LRC conditions, the Mach number would vary between 0.838 and 0.834 over this interval [3].


Acknowledgements

The author wishes to thank fellow IG members Mike Exner, Don Thompson, Sid Bennett, Barry Martin, Richard Godfrey, Tom Kenyon, and Henrik Rydberg for reviewing this report and providing insightful comments.

References

[1] Malaysian ICAO Annex 13 Safety Investigation Team for MH370, “Factual Information, Safety Investigation for MH370”, March 8, 2015, updated April 15, 2015.

[2] Barry Martin, Meteorological data for March 8, 2014, http://www.aqqa.org/MH370/models/NCEP/GDAS_FNL/gdas2014030800f00.txt

[3] Boeing, “Flight Crew Operating Manual, 777-200ER, Trent892”, June 16, 2008.

[4] Australian Transport Safety Bureau (ATSB), “MH370 – Definition of Underwater Search Areas”, June 26, 2014.

[5] Don Thompson, “Analysis: Malaysian Radar Surveillance Capabilities”, June 18, 2014, http://bit.ly/TUDM_ADS

[6] Ron Belt, “Analysis of Malaysian Radar Data”, May 29, 2014.

 


Further MH370 Debris Analysis

Further MH370 Debris Analysis

2015 August 05
Updated: 2015 August 06, 07 and 08
1. Preamble by Duncan Steel

In a previous post I provided a link to a paper by Mike Exner of the Independent Group (IG) regarding drift analysis of debris from the crash of MH370. Two other IG members have now prepared independent papers on this topic, which are available for download and inspection by any interested party: please see items 2 and 3 below.

At item 4 a link is provided to a recent ATSB update on the drift modelling.

Two new items 5 and 6 below have now (August 7) been added. The first (item 5) contains some observations on the apparent damage to the flaperon based on the photographs available on the internet; these comments come from a consulting engineer who needs to remain anonymous for employment-related reasons. The second (item 6) is a further set of observations regarding the implications of the flaperon damage, from Brian Anderson, a member of the IG.

Something that perhaps needs stating, and which has not been mentioned in most of the media reports so far regarding the flaperon found in Réunion, is the fact that the item in question may not have left the rest of the aircraft structure when it hit the ocean. It is feasible that the flaperon became disconnected whilst the aircraft was at high altitude, and then fell independently into the sea. An indication of this comes from: (a) The ragged trailing edge of the flaperon (with 40 per cent of its total surface area being missing), this being consistent with rapid ‘fluttering’ as would likely occur if the aircraft lost all control surface power whilst travelling at high speed, as would occur when the fuel was exhausted from the two engines and the APU, and before the RAT fired up and provided a new (short-lived) source of electrical power; and (b) The lugs holding the flaperon to the main wing structure appear to have been torn off in a manner that may be consistent with such violent fluttering (at 10-20 Hz) at high aircraft speed. If the flaperon did fall from high altitude, perhaps having left the aircraft at around 00:15 UTC, then it would have entered the ocean at some distance from the crash site of the rest of the aircraft.

This (free fall from altitude) might also be regarded as being consistent with the fact that the flaperon remained otherwise intact. An entry into the ocean at a speed around 500 knots/900 kph by the aircraft might be anticipated to cause gross fragmentation of the aircraft in line with what occurred in previous jetliner crashes of this type. However, if the flaperon tore loose from the aircraft at altitude then it would fall to the ocean under gravity but be impeded by air drag, reaching some terminal speed which would be anticipated to be lower (perhaps only 150-200 kph) despite the fact that it is aerodynamically-shaped, due to its large surface area to mass ratio (remember that it floats!). That is, the flaperon might well have dropped in a tumbling, spinning manner, and so hit the sea surface at a relatively low speed, limiting the impact damage.

This scenario – the flaperon being ripped off the aircraft by aerodynamic forces at altitude and then free-falling into the ocean – is supported by observations of the damage to the flaperon as given in items 5 and 6 below.

2. Paper by Henrik Rydberg

The paper by Henrik Rydberg is entitled MH370: Finding the Debris Origin, and is available by clicking here or here or here (252kB download; note that Henrik’s paper was updated on August 05 with a slight rewording, and the links above are to this updated version).

3. Analysis by Richard Godfrey

The analysis by Richard Godfrey is entitled Combined Inmarsat, Drift and Fuel Model, and is as follows.

I have attempted to combine the information available from the Inmarsat (i.e. satellite-derived data), oceanic drift modelling and fuel consumption/limitation models into one summary table, as below. A brief explanation of the content of the table is as follows. 

I have covered the latitudes from 10S to 43S in terms of start locations near the 7th arc. 

I have made use of the BFO error at 00:11:00 UTC assuming an aircraft altitude of 35,000 feet and a ROC (rate-of-climb) of zero.

I calculated the point reached on the 7th ping arc by assuming a continuation on the same track at a ground speed of 432 knots.

I then used the closest integer (latitude, longitude) point to the 7th arc location as the March 2014 starting point in the drift model of Erik van Sebille (see this paper). His data provide the time in months to reach Reunion together with a relative probability of doing so. 

I also made an estimate of the remaining fuel range at 00:11:00, assuming MH370 did not fly around in circles at some point.

There is only one place on Earth which meets the Inmarsat (BTO and BFO) data, matches the fuel range, and is likely to result in debris washing up on Reunion after 12 months. That location is 34S, 94E. 

RG_drift_table

This table is also available within a PDF document (rendering better legibility) available by clicking here or here (36kB).

4. Revised account of drift modelling on the ATSB web site

There is a new post on the ATSB web site regarding debris drift analysis; here is a link.

5. Observations on the flaperon damage from an anonymous consulting engineer

i. If one strut were to fail the other strut would likely follow (doubled dampening duty) if similar flaperon action/forces continued. Once struts fail and disengage the flaperon can rotate at high speed about the forward/bottom hinge points without much, if any, resistance. The struts could fail last, but because the hinges have structural design to hold the flaperon on the wing while the struts function to control movement, this makes the hinges the strong feature, and so less likely to fail first.

ii. The two forward/bottom hinge connectors appeared to have failed due to lateral movement of the flaperon in the inboard/outboard directions. The curvature of the remaining inboard hinge metal is indicative of the hinge developing a fatigue (yield) line prior to failure.

iii. Once that inboard hinge failed (if indeed it were first) then the outboard hinge would fail in a short instant at its weakest point. The inboard hinge indeed seems to have broken at its weakest lateral point: If you were strong enough to laterally wiggle the connector back and forth (like a spoon), it would break at the surface as shown in various photographs.

iv. This lateral movement could be generated from rapid load reversals created by a spiraling/turning aircraft.

v. If the flaperon forward/bottom hinges experienced a massive tensile direction forces (i.e. pushing the flaperon straight up until the point of failure) then they would likely fail at the hinge’s hole connector, not at the flaperon bottom surface connection point as in  the photos. In addition the flaperon body would likely be severely deformed due to the extreme forces required to ‘tear out’ the connector from the flaperon.

6. Further observations on the flaperon damage by Brian Anderson

i. The relatively large missing training edge (TE) piece has sheared off immediately behind the rear spar of the flaperon. It is at this point that I would expect the bending moment to be greatest, and hence the most likely failure line for at least two failure modes:
(a) aerodynamic flutter, and (b) impact from the engine or parts of the engine passing aft immediately after impact. The media suggestions of the damage being caused by the TE “dragging” in the water in a low speed or controlled ditching attempt, I think, ignore the fact that there is a massive engine hanging way lower immediately in front of the flaperons.

ii. The shape of the deformity around the attachment point for the outboard [NB: altered Aug 08] Power Control Unit (PCU) attachment points suggests that it was the inboard [NB: altered Aug 08] attachments that failed first, followed immediately afterwards by the outboard [NB: altered Aug 08] .

iii. The tearing of the whole flaperon away from the PCU attachment points is much more indicative to me of (a) above. I think an impact to the underside and TE should result in compressive damage to the leading edge (LE), and would be more likely to shear at the mounting points, i.e. hinges and PCU points, leaving part of the hinge brackets still in place.

iv. It seems significant to me that there is nothing remaining of the hinge brackets themselves, at either end of the flaperon.

Space Scientist, Author & Broadcaster