How Often Do Airlines Fly Into Areas Without Radar Coverage? (Ask Cranky)

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. Ask CrankyFor 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.

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24 Comments on "How Often Do Airlines Fly Into Areas Without Radar Coverage? (Ask Cranky)"

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Shane
Guest

Out of curiosity, since all long-haul flights seem to have that little flight map on the IFE based on GPS, wouldn’t it make sense that automatic signals are sent to the airline’s maintenance computers with the location and other stats of the flight? Or is there just too little utility to invest in obtaining and storing information that is 99.99999% unnecessary?

Simon
Guest

Also out of curiosity – if an aircraft encounters turbulant air then it will want to fly around it which means it would have to leave its booked route. I assume in radar-covered areas this is coordinated by ATC who make sure that everyone goes the same way around the weather and maintains separation. But what happens if a plane wants to leave its North Atlantic track? Or are they chosen each day to take routes which are as turbulance-free as possible?

The Traveling Optimist
Guest
The Traveling Optimist
Please clarify…. All aircraft have weather radar to detect adverse conditions. All aircraft have hard contact radar to detect other aircraft in the vicinity. All aircraft have INS (Inertial Navigation Systems) to plot flight paths and pinpoint their own exact locations on that track. If all of the above are true, ground based radar isn’t particularly necessary on overwater segments. In normal flight any aircraft and others around it know where it is. In the case of an accident, as Cranky pointed out yesterday, I’m curious why other aircraft ostensibly in that same area and equipped with hard-contact radar did… Read more »
jaybru
Member

Am I the last queasy flyer who still feels a little uneasy listening in on UA channel 9 on a flight to Europe when I hear that Canadian controller saying to my flight…”…radar coverage terminated. Good Night!”?

I look out the window and all I see is dark? And then turbulence! How many more miles ’til Shannon picks us up?

US Travel
Guest

Is it possible to get the exact location of airplane with the help of radar?
I don’t think so otherwise 9/11 couldn’t have taken place.

Nick Barnard
Member

I remembered something that provided a “faux radar” view of the ocean provided via data tramissions from the plane.

I haven’t had time to fully dig into it, but I think this is generated off of the Automatic dependent surveillance-broadcast system.. http://en.wikipedia.org/wiki/ADS-B

Basically the plane figures out where it is using GPS then it transmits it via satellite to the ground stations, and a computer generates the radar-like view from this….

Nimitz
Guest

How about TCAS? Does that work over the ocean? I suppose it also relies on radar interrogation. It really is a dark sky out there. Thank goodness it’s also big.

The Traveling Optimist
Guest
The Traveling Optimist

It may look and feel lonely but knowing the volume of traffic on any given night over the North Atlantic I’d know we weren’t the only ones out there.

If you want lonely, consider the half-dozen or so flights between California and Australia every night. Six thousand miles of open water with only Tahiti, Fiji and the Samoas sprinkled along the way. “Radar contact terminated” for sure!

Jay
Guest

Am I the last queasy flyer who still feels a little uneasy listening in on UA channel 9 on a flight to Europe when I hear that Canadian controller saying to my flight…”…radar coverage terminated. Good Night!”?

I look out the window and all I see is dark? And then turbulence! How many more miles ’til Shannon picks us up?

Well, of course, if everything goes to pot….it’s probably not going to matter that much if there are people “around” or not.

Just saying…..

Jim Spensley
Guest
Well Cranky you should save NextGen for another time and upgrade the radar coverage discussion to more accurate and objectives levels. The good news first: Ground based radars in the developed countries have just about line-of-sight range because of transponders. This means that an airliner can be located within a mile or two over 100 nautical miles from the ground radar. There are navigation aids, satellite phones, sometimes HF radios and other means for an aircraft to transmit its position and ETA to landfall. Commercial airliners have laser-gyroscope inertia systems good to about a nautical mile. Airliners equipped with cheaper… Read more »
Brendan
Guest

Shane – The IFE map is actually generated from data from the flight computers, not a GPS.

todd
Guest

to Nimitz
tcas uses mode s atc transponders. the mode s transponders on your airplane is searching for mode s transponders on other airplanes around.so then the tcas processor processes what altitude heading airspeed and if it see,s a airplane to close to you it will warn the flight crew plus the crew can see all the aircrafts that tcas see on there nd are dedicated tcas display. so yes tcas will work over the ocean. it docent need ground base radar. all the system tcas needs are all equipment of the aircraft

Jim Spensley
Guest
CF and interested others. In the NextGen concept, every aircraft would have a GPS receiver and a computer component that stores its GPS-determined positions every so often. The NextGen ADS-B transceiver on each aircraft would send its position plus the plane’s identity to other aircraft and ground stations within 150 miles. There may be 450 or more aircraft and ground stations within 150 miles. The GPS data transmissions must be synchronized, broadcast one at a time. This is when the ground radar beam illuminates the aircraft, just as in the current transceivers. As I said, just about the same for… Read more »
Graham
Guest

Brett,

I was recently on a turbulent Cape Air flight that spent much of the time in the clouds. I asked the pilot how they avoided collisions in the clouds with GA aircraft. He said that the pilots talk to each other and ATC would see if there was a problem. However, what contact do they have under VFR? Are they always on someone’s screen and at someone’s direction?

Thanks,
Graham

Jim Spensley
Guest
The discussion is getting pretty far afield if the topic is over the ocean navigation and re-entering air traffic controlled airspace. Air Traffic Collision Avoidance (ATAC), Aircraft Digital Position – Broadcast (ADS-B), and transponder radar returns are related but not compatible ways to deal with relative positions of aircraft in flight. Position data or navigation “fixes” are used to adjust direction and speed to reach a fixed point at a planned time. The realtime application of position to collision avoidance or air traffic control separations depends on forecasting future positions from a time-history of positions — tracks. In general, decisions… Read more »
Jeremy
Guest
I guess I hadn’t given the radar coverage much thought. I sort of presumed (incorrectly) that GPS transponders filled in the gaps in ground-based radar coverage. Much of the world’s shipping is fitted with AIS (Automatic Identification System) and transmits position, course and speed at regular intervals. This is a VHF system… AIS is required on all ships over a certain tonnage and for ALL passenger ships. Wikipedia (everyone’s best source!) indicates that as many as 40,000 ships are fitted with AIS. Would this be similar to the “NextGen” technology you said you’d discuss in a future post?
Simon
Guest

I’m sure I could come up with a ballpark figure myself – but roughly how many flights are over the N Atlantic at once each night?

Jim Spensley
Guest
Perhaps we should wait to look at NextGen and address what technology is available for tracking aircraft over the oceans. A. NOT ground -based FAA radars or EU or Asian or Austrailian air traffic control radars. B. Aircraft that do fly in US or EU airspace use radar transponders to extend the range of ground radars and to tag tracks with aircraft identification codes. The coverage includes various over-ocean jetways. C. In the US and the EU, enroute air traffic control coverage is thorough for jetways but incomplete in some places, including some fairly large areas in the western US… Read more »
Jim Spensley
Guest
The link given by CF says:”NextGen is an umbrella term for the ongoing, wide-ranging transformation of the United States’ national airspace system (NAS). At its most basic level, NextGen represents an evolution from a ground-based system of air traffic control to a satellite-based system of air traffic management. This evolution is vital to meeting future demand, and avoid to gridlock in the sky and at our nation’s airports. The second sentence is misleading. Also, the “transponders will broadcast if on ” statement by CF. The radar transponders transmit when stimulated by a ground radar signal, and this carries the direction… Read more »
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