Investigation officials have stated that the last radar capture of MH370 was a target in the Malacca Strait about 10 NM past waypoint MEKAR on airway N571, recorded at 18:22:12 UTC. Unfortunately, this last capture occurred before MH370 made its final turn to the south. The location and timing of this turn has been the subject of much debate because it has a significant impact on where MH370 crossed the 7th arc, and therefore it is important in defining the underwater search area. If we assume the aircraft was flying level after the log-on at 18:25 UTC, then the BFO data tells us the turn to the south must have occurred no later than 18:40 UTC. However, if we are open to the possibility that MH370 was descending at 18:40 UTC, then the turn to the south might have occurred after 18:40 UTC.
In the ATSB report released on June 26, 2014, we learned that there might have been other radar sources in the area that could give us hints about the path of the plane. There is the statement “The aircraft passed close to a NW point at 1912”. However, the report gives no indication of where that radar source was located, and whether there was a definitive capture. Because any radar captures after 18:22:12 UTC would provide important clues about the final path, there is interest in learning more about this “NW point”.
Researcher Dr. Niels Tas asked the ATSB about the NW point, and received the following reply: “The NW point at 1912 was an assumed theoretical location at 8° 35.719’N, 92° 35.145’E initially chosen to provide clearance from the known radar sources (mainly Singapore). A line from IGREX to the 1912 point was used as an upper bound for the airplane performance work after loss of radar contact (the min flight distance would be turning south right after loss of radar). This point did not affect the Doppler analysis, just the fuel burn, which affected the range measurements. Analysis had included using the upper bound (IGREX/1912 point) and the lower bound (direct from the 1822 point)…”
This response provides us with some clues about the radar source. First, we have a precise position for the NW point, which puts it in the Indian Ocean to the west of the Nicobar Islands, and about 15 NM to the right of a plane traveling along airway N571 between waypoints IGOGU and LAGOG. Second, we learn that the radar source is an asset of Singapore. Because Singapore is about 800 NM from the NW point, it is impossible that the radar installation is land-based in Singapore. If not land-based, it is mobile, and possibly airborne.
It is well-known that Singapore has significant airborne radar capabilities. In 2012, Singapore announced that an additional four Airborne Early Warning and Control (AEW&C) aircraft were operational, to complement the first it has fielded in 2009. These G550-EL/W-2085 aircraft were purchased from Israel, and are Gulfstream 550s fitted with phased-array radar. The reported range is 200 NM.
I asked the ATSB for more information about the NW point. Because the radar source is a military asset, much of the information is protected. However, I was able to learn that the NW point was shared by a member of the Joint Investigation Team (JIT), which consists of personnel from Malaysia, Australia, China, the UK, the US, and France. The NW point is not an actual radar capture, but was used in early path models as the latest time and position for the turn to the south. Basically, if the turn had occurred to the northwest of this point, it would have been detected by the radar source. I also learned that this radar source had no coverage of the Andaman and Nicobar Islands. Finally, I learned that this radar source had no coverage of any of the high probability paths predicted by the ASTB.
I was interested in determining where the airborne radar might have been, and whether the lack of radar captures might help us exclude certain paths that would fall within its range. In particular, I was interested to know whether the lack of detection might preclude a path between Car Nicobar and McMurdo Station. I proceeded with the following assumptions:
- There were no radar captures after 18:22:12 UTC.
- The range of the airborne radar was 200 NM.
- The NW point is at the limit of the range of the airborne radar.
- The airborne radar was in a tight holding pattern and never was very far from a fixed location.
- All of the Andaman and Nicobar Islands were beyond the range of the airborne radar.
- A path reconstructed with a turn at 18:40 UTC (the latest turn considered by the ATSB) would be beyond the range of the airborne radar.
The results from the analysis are shown in the map below. A circle with a radius of 200 NM defines all possible points at the range limits of the radar. Therefore, the position of the airborne radar would be somewhere along this circle. Possible radar positions that satisfy the criteria listed above fall on an arc between the red and green stars. Points to the northeast of the red star would have allowed radar coverage of portions of the Andaman Islands. Point to the southwest of the green point would have allowed radar coverage of some of the high probability paths reconstructed by the ATSB.
If the radar source was located at the orange star or to the south, MH370 would have been seen if it followed a path between Car Nicobar and McMurdo Station. However, radar positions along the arc to the north of the orange star would not have seen MH370 if it traveled along this path.
It’s therefore possible that if an airborne radar source was circling about a fixed location somewhere along the white arc between the orange and red stars, it would not have seen MH370 if it flew towards McMurdo Station.
But here’s a related question: Why was Singapore possibly operating an AEW&C asset in the Indian Ocean to the west of the Andamans and 800 NM from Singapore?