primary and secondary surveillance radar system in Hong Kong

 

There are two principal types of radar system used for ATC, namely
primary surveillance radar (PSR) and secondary surveillance radar (SSR). A
PSR transmits radar pulses and detects the reflected signals from the aircraft
concerned. It provides information on the range and bearing of aircraft in the
form of a target blip on the radar screen. 

An SSR provides information on the position, altitude and identity of aircraft in the form of target label on the radar screen. It does so by transmitting interrogation signals to trigger the transponder on board an aircraft, which in turn transmits special coded signals back to the SSR to provide the concerned information. Thus, effective operation of an SSR is
subject to the availability and proper functioning of the aircraft’s transponders.
Not all aircraft have transponders. Some military aircraft, for instance, do not.
 

A PSR, on the other hand, does not rely on any transponder. To provide an
adequate radar picture with a continuous display of aircraft target, both PSR and
SSR are essential.

The existing PSR network to support the ATC in Hong Kong
consists of three PSRs, which provide approach, medium range and en-route
control respectively. They are –
 

(a) Approach Surveillance Radar (ASR) at Sha Chau, providing a short range
coverage up to 64 NM;
 

(b) Terminal Area Radar (TAR) at Tai Mo Shan, providing a medium range
coverage up to 140 NM; and
 

(c) RSR at Mount Parker, providing a long-range coverage up to
200 NM.
 

The ASR and TAR were commissioned in 1997 and 1998
respectively and specifically designed for the new HKIA. The RSR, installed in
1978 for the then Kai Tak Airport, was not replaced at that time as its useful life is
estimated to be up to 2003-04.

At present, there are four SSRs in Hong Kong, three of which being
paired with the three PSRs mentioned above. The fourth SSR
serves as a backup. Such overall radar network configuration was recommended
by the Airport Master Planning Consultants and has proved to be appropriate
based on operational experience gained since the opening of the HKIA.
 

For aircraft located outside 200 NM from Hong Kong, CAD applies
procedural control whereby aircraft are separated using “time” standards
(typically ten minutes between aircraft following the same route at the same
altitude, equivalent to approximately 80 NM in distance). When aircraft are
being controlled and separated using radar, the minimum distance between
aircraft may be reduced to 3 to 10 NM depending on the location of the aircraft
and the radar equipment in use. The procedural control obviously cannot cope
with a high volume of air traffic which is typical in the airspace within 200 NM of
Hong Kong. Therefore, CAD needs to use radar with adequate performance to
ensure a safe, orderly and expeditious air traffic flow within about 200 NM from
Hong Kong.
 

The current proposal is to maintain the effective operation of one of
the components of Hong Kong’s entire ATC system. There is also a need to
enhance ATC operations at the system level, which is the subject of a separate
proposal for Members’ consideration vide FCR(2000-01)70.

HKATC air traffic surveillance