Here’s a very timely Ask Cranky that was spurred by the Air France accident earlier this week. I’m sure many of you heard that the airplane was flying in an area where there was no radar coverage, and that might be surprising. You may have had these same questions . . .
How often do commercial airline flights fly into areas without any radar coverage?
Where are these areas that lack radar coverage?
Tom
It may surprise you to know that most of the world is not covered by radar. Part of that is a technical challenge. Our air traffic system runs on ground-based radar, and most of the world is covered in water. It’s kind of hard to plant something that’s ground-based into the ocean. 
For that reason, once you’re more than a few miles off the coast (as was the Air France aircraft), you’re going to be out of radar range.
But even over land, radar coverage isn’t always stellar. For example, there has been much discussion about Brazil’s gaps in radar coverage over the Amazon over the last few years.
So is this a huge problem? Well it’s certainly not ideal, but it’s not dangerous either as long as proper procedures are being followed.
Look at the North Atlantic, for example. That is one incredibly busy area every single day with tons of traffic going between the US and Europe. So how do they handle all that traffic without radar? They introduce inefficiencies to keep planes far apart.
First of all, the North Atlantic operates under a track system. So every night, winds are taken into account and certain tracks are used by all airplanes. Eastbound and westbound airplanes fly different tracks at different altitudes – it used to be 2,000 ft differences but now it’s been reduced to 1,000 ft. (Those vertical separations are used over land as well.) They also have started to fly a mile or two off-center of the track to provide even more protection from a mid-air collision. There is also greater separation introduced between airplanes on the same track to give them some leeway.
So as you can see, it’s not dangerous but just slightly inefficient. It is important, however, to note that weather radar is a different story. Every commercial jet flying has weather radar to help it avoid storms regardless of whether it’s over land or ocean.
One of these days, we’ll finally have GPS systems throughout the fleet that will fix this issue once and for all. But we’ll talk about “NextGen” in another post.
