Radar Screens and Aircraft 'blips'

[sharpclassic]

Hello all,

Question from a pilot to all you controllers.....

Are there any circumstances under which a controller may not see the 'blip' of an aircraft on his/her screen?

e.g. 2 aircraft cruising in the airspace of a large European nation, both at the same FL on reciprocal headings in the same airway.

Thanks very much!

SC

[Spitoon]

Yes - lots of reasons. Depends on type of radar, mainly primary or secondary, and in the latter case whether the aircraft is transponding. With primary, the strength of a target can vary substantially for no immediately obvious reason.

Also, on the display, certain targets may be filtered out routinely although the controller can always 'unfilter' a target if he/she needs to.

[Liobian]

I believe there's also been an occasion when an incident occurred, involving a biz-jet and an a/c of composite construction. IIRC, the latter's airframe did not provide a usable primary echo, whilst its single SSR aerial was shielded (from the ground interrogator) by the attitude of the a/c at the time. As usual, the 'holes lined up'. It may not be a common occurrence, but there's more and more of them out there.

[supraspinatus]

There are areas without proper radar coverage, both primary and secondary. These areas are usally below MSA.
There is also a "cone of silence" directly above the radarsite.
Aircraft on reciprocal tracks are not on the same level. If for some reason the tracks are both east- (or westbound), and both a/c are on the same level, the controller is there to ensure separation.

Are you afraid of flying?

[sharpclassic]

Thanks for the responses so far guys...

Supraspinatus,

Yeah, I know that when on reciprocal tracks, aircraft aren't meant to be at the same level, but when you get a "Traffic, Traffic... Decend, decend" at FL350, someone has messed up!

[121decimal375]

There are also places in the UK FIR which do not have radar coverage nd are procedural enviroments at all levels

[121decimal375]

"Yeah, I know that when on reciprocal tracks, aircraft aren't meant to be at the same level, but when you get a "Traffic, Traffic... Decend, decend" at FL350, someone has messed up!"

It could also be that the other aircraft is not at the same level but is within close proximity with a high climb or decent rate! TCAS could just as easy be triggered in these circumstances

[supraspinatus]

The most common reason for TCAS RA is level busts in busy sectors.

Back to your question: Are there any circumstances under which a controller may not see the 'blip' of an aircraft on his/her screen?

There are many. Is there a specific incident you are thinking of? May be easier to answer if I knew why you where asking.

[5milesbaby]

sharpclassic: the obvious isn't always what it seems. If you have had an incident then don't assume anything - if the other traffic was military then you are in a completely different set of rules and regulations.......

Not assuming anything but that does answer quite a few questions such as yours.