Aug 31 2006

GPS Not A Threat To Airlines

Published by at 8:23 am under All General Discussions

I have to disagree with Michelle Malkin and other who are worried that GPS Receivers are a threat to anyone. They rely on the fact that terrorists were looking into GPS receivers. The fact the terrorists thought these devices could help them only shows how little technical understanding they had of the devices. As a NASA engineer who deals with GPS receivers used to fly satellites in earth’s orbit I hopefully can clear this up.

First off, GPS receivers are radios that recieve signals – they do not transmit. They are therefore less dangerous than a cell phone in that respect. GPS receivers listen to signals from satellites in earth’s orbits, noting the time it takes the signals to reach the receiver from four satellites so the reciever’s position and velocity can be computed. So it will tell you were you are. So did graphics on the planes for a while.

Knowing where you are is not going to give you much help in targetting a spot on the ground (which is what I assume some people are worried about). GPS receivers need to be tied into the avionics of the airplane (and are already) in order to fly an airplane to a specific point. If the terrorists can reach the cockpit and avionics they don’t need their own GPS receiver. And the GPS receiver in coach can do nothing to the avionics.

I agree the current restrictions are difficult, but C4 in the shape of a lipstick, from enough passengers, is a true and real threat to an airplane. Such is the world we live in. Think how much worse this would be if we could not monitor terrorists overseas and their financial transactions!

6 responses so far

6 Responses to “GPS Not A Threat To Airlines”

  1. MerlinOS2 says:

    Another point AJ is that most commercial GPS recievers will cease to function correctly at over the earth movements at about 80 mph velocity.

    Some have proposed that this was a deliberate limitation to prevent certain “alternative” uses.

  2. S. Naylor says:

    I have to disagree Merlin. I’ve used GPS (2 different models) many times while flying (as a passenger – in coach) to various place on the globe over the past 5 years. They work fine at least up to 590 knots & pretty mucch match the aircraft’s position display on those flights where it’s available.

  3. AJStrata says:

    S. Nayl0r,

    I agree. There are flight GPS systems and we at NASA use them on satellites. There were some adjustments need to the kalman filters that do the position-velocity estimates (or sats fly at thousands of mph) so the data wouldn’t be seen as a noisy outlier (yes, we are actually going that fast!). But that is not a big change. The point is nearly all commercial airplanes I would assume have a GPS navigator in them (I know the military jets do) where you set way-points and let the auto-pilot do its thing.

  4. MerlinOS2 says:

    It was my understanding about the “early” handheld models, thanks for the updated info.

  5. For Enforcement says:

    Yea, there is a lot of information and mis-information about GPS. Many years ago, I had one of those laptop software programs and it worked great. I was using it on an airplane and it displayed the speed very well and was in agreement with the plane’s speed. No one objected to my using it. Fast forward a couple years and I had a Magellen handheld and it worked great on airplane also. Flight attendent saw I had it, now this was about ’98 or so, and she had a conniption. You can’t use that, it sends out signals that interfere with the plane’s navigation. I assured her it didn’t, but I turned it off as she requested.
    I happen to be a private pilot, and believe me, almost ALL planes, including private, have GPS that is linked to autopilot. They are so accurate you could actually let them take off and land for you. Of course no one does, but they work that well. You can easily put in waypoints with speed, altitude, etc and it will follow it to a tee, including putting you on final approach. Then the pilot takes over. At the worst, a system on a private plane might be off 30-50 feet altitude. (That’s why pilot does the actual landing) I understand military is much more accurate tho.

  6. pull says:


    I believe that effect would be because we used to have receivers be off by a number of feet… because of the danger of using these for missles and such. This regulation was later taken away.

    On the topic:

    I have been using various gps’ for about ten or fifteen years, not sure. I do not like to depend on them for hiking, but they are an useful tool. Nowadays, they are built into many portable devices and the watch models are actually useful. It is surely not a threat.

    Personally, I think that blowing up planes should be the least of our worries, ultimately. I guess a lot of people have a lot of fear dealing with flying. It does strike at the heart of modern commerce. Their next big attack is more likely to strike one of NY’s bridges or tunnels, like they said they would before… back in 93. Granted, there are so many weak spots where they could kill a lot of Americans and get away with it… or induce widespread fear.

    Our food sources are probably the biggest concern for me. There are a lot of weaknesses there. Sniping is always an option for them. Or, random serial killing at more close range. If the body is left and they make no interaction… there is not even DNA evidence. Explosives can be made out of just about anything… and gas lines run about everywhere (and can be trivially heated to explosion).

    Heh, GPS are not in my list there. I don’t think they are worrying about missle guidance systems anytime soon. Maybe Iran will next year, but they would be better off hitting us without a missle, but with a portable attack… even if we don’t have any chance of shooting a sucker out of the sky.