Civilian radar data after transponder was disabled. (Click to enlarge.)
We know that MH370 was captured by civilian and military radar sites before and after the transponder was disabled at 17:21 UTC. However, Malaysian authorities have chosen to release these data sets only as low resolution images that have imprecise position information with few timestamps. The DSTG did choose to publish in its Bayesian analysis the speed and track data that was derived from radar data that was provided to them by Malaysia. However, the DSTG presented the speed and track data after applying a Kalman filter to remove noise. It’s unknown whether that Kalman filter produced artefacts in the graphical presentation of that data.
We now have what we believe are the data sets for the primary surveillance radar (PSR) and secondary surveillance radar (SSR) from Malaysian civilian radar assets. The PSR data is of particular significance because it provides additional insight about how MH370 was flown after the transponder was disabled at 17:21 UTC. The data was publicly released by fellow IG member Mike Exner. The military radar data remains unavailable.
The data begins at 17:30:33 when the civilian radar installation at Kota Bharu Airport (WMKC) detected MH370 traveling back towards the Malay peninsula about 58 NM from shore. The last radar target was captured by the civilian radar installation at Butterworth Airfield (WMKB) after MH370 had passed to the south of Penang Island and was tracking northwest up the Malacca Strait towards Pulau Perak.
Some initial observations about the data:
- The PSR data is similar to the civilian radar data that was graphically presented in the Factual Information (FI) from March 2015. However, while the last civilian radar capture in the FI was at 17:51:47, the new data set has captures until 18:00:51.
- The path derived from the Kota Bharu radar data is not straight. More analysis is required to determine if this waviness indicates that there were pilot inputs from manual flying, pilot inputs to the selected heading with autopilot engaged, or inaccuracies of the radar data.
- The path was tangent to a 5 NM radius for both Kota Bharu and Penang Airports. This may indicate that these airports might have been displayed as fixes in the navigational display (ND) with a radius of 5 NM and used as navigational references.
- After passing to the south of Penang Island, the plane first tracked towards 301ºT, and then changed to 291ºT, which aligned with Pulau Perak and roughly towards VAMPI.
- The groundspeed data as derived from the radar data is noisy, reflecting uncertainty in the value of the timestamp as well as the range and azimuth for each capture. In light of the uncertainty, the average speed was calculated for five of the six segments of radar captures, and shown by the red line in the figure below. (The time interval of the shortest segment was only 24 s, and deemed to short to calculate the speed with a useful level of precision.) The average speed for the second and third segments are 527 knots and 532 knots, respectively, which suggests the plane was flying close to Mmo=0.87. For instance, with a tailwind of 12 knots and a temperature offset of ISA+10.3K, a groundspeed of 527 knots converts to M0.87. At the Mmo/Vmo crossover altitude of 30,500 ft, a groundspeed of 532 knots converts to M0.86. This suggests that after the aircraft flew past Kota Bharu, it was at the upper end of its operating speed range, and possibly at times beyond it.
Calculated groundspeed as derived from the civilian radar data. (Click to enlarge.)
I know that independent investigators that contribute here and elsewhere will continue to analyze the data to better understand how MH370 was flown before it completely disappeared from all radar sites.
Update on April 12, 2018: The plot of groundspeed was updated by removing the trend lines and replacing them with average speeds over segments. In light of the noise on the speed calculations, this is more appropriate. The estimated peak groundspeed reduced from 545 knots to 532 knots. The corresponding text in (5) was also updated to reflect this change.
Update 2 on April 12, 2018: Here is an Excel file for those wishing to see the basis for my calculations. Please let me know if corrections are required.