In the late 1970s plot extraction equipment was introduced, this took the primary and associated secondary radar outputs, combined and processed them before sending them over telephone lines to the L1.
22.
At 01 : 07 MYT, the aircraft was at flight level 350 approximately above sea level when the final message using the secondary radar to track aircraft . No distress call was made.
23.
But an FAA spokesman said that secondary radar was lost on the first sweep and restored on the second; by the third sweep, the spokesman said, secondary radar showed location but not altitude.
24.
But an FAA spokesman said that secondary radar was lost on the first sweep and restored on the second; by the third sweep, the spokesman said, secondary radar showed location but not altitude.
25.
Furthermore, it cannot always estimate the altitude of an aircraft . Secondary radar overcomes these limitations but it depends on a transponder in the aircraft to respond to interrogations from the ground station to make the plane more visible.
26.
No attempt was made by either the Embraer or Brasilia Center to contact each other from 15 : 51 until 16 : 26 when, 24 minutes after the loss of secondary radar contact, Brasilia Center called the Embraer and received no reply.
27.
AHeenen states " Since the location of the aircraft is a fact, not a creative work, and the map traced purports to show the path that Flight 370 traveled based on primary & secondary radar, the flight path is not subject to copyright"
28.
The following day, Hishammuddin Hussein, the acting Malaysian Minister of Transport, refuted the details of " The Wall Street Journal " report stating that the final engine transmission was received at 01 : 07 MYT, prior to the flight's disappearance from secondary radar.
29.
If controllers know that a big flock of birds is on the way, they can turn off the primary radar system, the one that reads echoes back from objects in the sky, and rely on secondary radar, or the messages sent by the transponders.
30.
By 2005, China had installed 31 primary radars, 52 secondary radars, more than 1, 000 Very High Frequency ( VHF ) communications systems, over 160 Omnidirectional Range and Distance Measurement Systems ( VOR / DMEs ), and more than 140 Instrument Landing Systems ( ILS ) ( see Distance measuring equipment ).
