How did primary radar and military radar track MH370 after its transponder stopped on March 8 2014?
Executive summary
Primary radar (the non‑cooperative "ping‑and‑listen" radar) and military radar provided the only direct post‑transponder evidence that MH370 turned away from its filed track and flew back across the Malay Peninsula, but their coverage was patchy, the raw military data has never been fully released, and long‑duration Inmarsat satellite handshakes — not radar — supplied the hours‑long record that guided the underwater search .
1. What “primary” and “secondary” radar mean and why the transponder matters
Civilian air‑traffic control normally depends on secondary radar, which interrogates an aircraft’s transponder to get identity and altitude; when MH370’s transponder and ACARS stopped, the secondary‑radar symbol and altitude data vanished from controllers’ screens, leaving only primitive primary‑radar returns where coverage existed .
2. How military primary radar picked up MH370 after the transponder went silent
Malaysian and nearby militaries were operating longer‑range primary radar that does not rely on a transponder, and those systems recorded a return — a tight turn and a westward track back across peninsular Malaysia toward the Strait of Malacca — after the aircraft disappeared from secondary displays; this military primary‑radar picture is the basis for the assertion that the aircraft was hand‑flown during its early diversion .
3. The geographic and technical limits of radar coverage that constrained the picture
Primary‑radar detection ranges vary by site and are limited by line‑of‑sight and horizon; civilian primary radars such as Kota Bharu's had shorter nominal ranges and did not see the later turns, while some military primary‑radar installations with greater range recorded the turnback — a disparity that left investigators with intermittent snapshots rather than continuous vector data .
4. What the public record contains — and what it doesn’t
Although press reports and investigators cite military radar as documenting the initial turnback and the last military radar contact at about 02:22 MYT before the aircraft headed south over the Andaman Sea, Malaysia has never released the full raw military radar logs, meaning independent researchers must infer timing and precision from secondary summaries and leaked or partial datasets .
5. Why satellites, not radar, defined the long end‑to‑end track used for searching
After radar contact was lost entirely, MH370 continued to exchange hourly “handshakes” with an Inmarsat geostationary satellite for several hours; analysis of those satellite communications — including Doppler and timing measurements — produced the southern‑Indian‑Ocean arcs and the long‑duration timeline that determined the underwater search areas, because radar coverage simply did not extend across the vast ocean where the aircraft is believed to have ended .
6. Alternate interpretations, agendas, and the limits of certainty
Alternative analyses point out that military primary‑radar returns can be less precise than transponder‑derived secondary data and that some early conclusions (for example, whether the turn was manual or automated) depend on interpreting imperfect radar snapshots and incomplete datasets; investigative groups and media outlets have various incentives — from national reputations to commercial interests in new search contracts — that shape which pieces of radar and satellite evidence are emphasized in public reporting .
7. The practical takeaway for what radar actually proved
Primary and military radar established that, after the transponder stopped, MH370 did not simply vanish on its last filed heading: it turned and flew back over Malaysia and then out toward the Andaman Sea, but those radar traces were intermittent, regionally bounded and, without release of the raw military logs, cannot alone locate the aircraft’s final resting place; for that, investigators relied principally on Inmarsat satellite data and later debris and drift studies .