Where is the airspace not covered by primary Radar? Most ATC in the world rely primarily on secondary radar to know where planes are. This requires that the transponder on the plane works correctly.

This means that maintenance and deployment of primary radar is no longer a primary concern for airspace regulation. It becomes at best a secondary backup system before they need to pull out the flight progress strips and airways charts.

Where are the spots that is not covered by primary radar? I understand that some military ships have primary radar and can act as a mobile radar during operations.
There are a few spots not covered by primary radar. Here are a few I can think off:

Afghanistan, not really what you'd expect from flying between Europe and South East Asia. I was told though by the pilots that the Americans were keeping an eye on us. I'd imagine there are a few holes in the CIS countries as well.

Multiple areas in Africa, but this is improving I believe. There's a post on PPrune. Apparently known as the 'dark continent' for spotty coverage and consistency. South Africa has good coverage, and I'd guess the same for much of northern Africa as well.

A few remote areas in South America, then again, improving.

Oceans are not covered.


Determining factors are population density, aircraft density and economic development.

As more you Malaysia map, if there's a radar at Kota Bharu [KBR] airport, here's the map assuming a range of 200 Nm for the radar. It should in theory be well within reach.

(source: gcmap.com)
And an extended version:
SGN Ho Chi Minh City (Saigon) [Tan Son Nhat Intl], VN
KUA Kuantan [Sultan Abmad Shah Airport (Pedang Geroda Airport)], Pahang, MY
KUL Kuala Lumpur (Sepang) [Intl], Selangor, MY
KBR     Kota Bharu [Sultan Ismail Petra], Kelantan, MY

(source: gcmap.com)
Just for the interested, here's a map showing Japanese military radar, just to get an idea of coverage in a country full of people and planes.

Maps from http://www.gcmap.com/