Malaysian Acting Transport Minister Hishamuddin Hussein, Chief of Defence, Chief of Royal Malaysian Air Force and other officials held a press conference about an hour ago. Here is one of the replies by RMAF Chief of Air Force
“Q: Did the aircraft turn back?
A: There is a ‘possible’ turnback. Why ‘possible’? Because we are trying to corroborate with all radars, including civil radars. We have been very consistent in what we have been saying in the last few days. The target disappeared at 1:30 in the morning. Primary radar didn’t pick it up at that point in time. Defence primary radar was analyzed same day. Indication of possibility of air turn back. That’s why search was conducted in Straits of Malacca.
The last plot was at 02:15, 200miles northwest of penang. But doesn’t give identification of aircraft”
In the press briefing that lasted more than 30mins, officials patiently gave many explanations to the press whom has little understanding of radar. Here are a few important terminologies mentioned above explained in layman that you might need to know as more radar news unfolds
Primary Radar: The form of radar that most people would understand. Similar to how echo works, the radar gives off a pulse into the air and aircraft is detected when the pulse bounces off the aircraft and received by the radar. The returned pulse is processed and will appear as a plot on the screen, giving only the bearing (direction/azimuth) and range of the aircraft. Only a 3D radar will provide the altitude of the aircraft. The returned signal is usually weaker after traveling to and from the radar.
Secondary Radar: Secondary Surveillance radar (SSR) is a common but less known form of radar. These radar sends out a pulse with is received by the aircraft, a transponder on the aircraft will reply information of the aircraft in codes, such as its identity in the form of 4 numbers (Squawk Code) and altitude taken from the aircraft’s systems. As secondary radar is two ways interrogation, the range is normally further than a primary radar.
Primary and Secondary Radar are usually mounted together and but however, it is not uncommon that primary radar functions alone. As seen above, civilian and defence radar operates independently from each other. In the picture above, the secondary radar (the longer rectangular piece) on mounted on the primary radar.
Plot: The raw returned information that appears on the radar screen from a primary radar. It is usually a speck of dot / circle with no other information other than the range/ bearing and altitude. As mentioned above, primary radar returns are usually weak depends on the range of the aircraft, and will come and go on the screen. Dense clouds or even flock of birds can appear as plots on radar.
Track: The processed information from the primary and secondary radars, with the identification of the aircraft, altitude, and plot information forms a ‘track’. Systems software will make sense from the input of various radars, flight plan database etc to create these tracks. Usually in a ATC radar it will also have the instructed heading and altitude keyed in by the controller.
Although it is possible to control an aircraft with just only track or plot, it is best to have both track and plot for a positive identification of the aircraft.