Expert: Ismar Avdic, Eng. - 8/31/2009

Question
QUESTION: In the commercial aviation industry, how accurate is the radar that is used, to the mile? I saw one site that indicated + or - 2nm for a distance of 250nm away from the radar. That seems pretty accurate to me and I sort of assumed that if much closer, then the accuracy would be that much better or would certainly reliably improve as an aircraft got closer to the radar source.

ANSWER: Hi Jen,
Yes you are right radar is pretty accurate. Although depending on distance accuracy is higher vs lower. In USA there is numerous radar center to get coverage, so in reality you are almost always close to 1-2 mil accuracy. Other parts of world with wide spread radar stations or their locations there is areas of blank coverage. Even in USA we have experience blank spots where radar coverage is actually on/off due to terrain expecially in mountain terrain like Colorado.

Ismar


---------- FOLLOW-UP ----------

QUESTION: Yes I do. right now I am having a very difficult time finding a distance that is accurate. That distance is from the Eastern boundary of the Indianapolis Air Space Center zone (ZID), to the Pentagon building. This zone boundary, I assume, is also the Western boundary for the Washington Air Space Center zone (ZDC). Parts of both run north/south and I am guessing this is the part I need distance from.

Thanks if you can help with that/those figures.

Answer
Hi Yen,
Estimate and then add safety factor of 20 procent. I do usually do that as pilot. Although our Garmin units are really on neddle considering showing current position.
It sounds to me that you working as ATC person, or you are pilot. In either case if unsure your present position from centers estimate and just check with other center to "verify" distance for particular airplane from their coverage.
As we mention before radar accuracy is not always exact depending on coverage sections and distances from unit, disturbances in weather, electromagnetic disturbances and so on.
But in general they are dependable.

Ismar