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Guiding Air Traffic Sans Radar With GPS
CamMac writes: "UPS Aviation Technologies, a subsidiary of UPS, helped in developing a new air traffic control system called ADS-B in which the aircraft broadcast their position, altitude, and airspeed to each other and the ground based on GPS data. This is all done without radar, so it is effective in remote areas or in mountainous terrain. It also displays all this information to pilots as well as ground control, so that aircraft are no longer dependant upon crypic orders from the gound to understand where everyone else in the sky is." Besides being a smart way to take advantage of all those GPS satellites, this also lends plotline cues for remakes of such classic cinema as Goldeneye, Diehard II and Airplane.
SA (selective availability) is an intentional dither introduced into the commercial, non-encrypted GPS signal. SA has now been discontinued, allowing commercial receivers to provide much more accurate results.
The GPS broadcast also includes a military sub-band, which is encrypted. The military portion of the GPS stream provides greater accuracy (for both position and time). Encryption has not been discontinued, for exactly the reason you point out (subversion), as well as to avoid providing military-level accuracy to our foes.
That is, a (civilian) GPS would not work at a speed above 200 miles per hour, reportedly to prevent terrorists from using it to guide smart bombs to their targets.
Disclaimer: I am extremely biased in this area, due to the fact that my father was killed in an airline crash in April 1977 (read all about it in Chapter One of Air Disaster (Vol. 2), by Macarthur Job). The main problem there - the plane flew smack into the worst part of a severe thunderstorm, which onboard weather radar showed as a clear spot. Both engines died, and despite having three airfields relatively close by, they attempted to land on a two-lane country highway. Admittedly both ground and airborne radar systems have come a long way since then, but they are still not enough. GPS might have let them know where the closest airport was in time, if not warning them off from the storm in the first place. If a real-time ground-based color Doppler radar display could be piped into the cockpit, along with accurate GPS positioning, I would think quickly developing weather systems would be much less dangerous for all classes of aviation. However, the bandwidth problems for something like this might be insurmountable for quite a while, despite this company's claims.
#include "disclaim.h"
"All the best people in life seem to like LINUX." - Steve Wozniak
#include "disclaim.h"
"All the best people in life seem to like LINUX." - Steve Wozniak
It's not just because of the intermittent inaccuracy of GPS that you'd want to keep radar as a backup- what if a solar flare comes along and knocks out several satellites over a busy flight route? Having a ground based backup system handy for such an event is a good idea. I would hope that someone would realize that before scrapping radar entirely.
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brave little toaster
"Remember, don't try this at home until the statute of limitations has expired."
Not in altitude. From 18000 feet to 30000 feet (IIRC), the minimum allowable vertical separation between two aircraft traveling in opposite directions is 1000 feet. I don't know what the minimum allowable horizontal separation between two aircraft flying at the same altitude is, but it's at least a mile.
Since GPS is least accurate in measuring altitude, this might be an issue...
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The idea of a '747 virus', IS intriguing. Fortunately, I doubt that aircraft will do software downloads in mid-flight.
Free Software: Like love, it grows best when given away.
Somehow people assume that every clock is 100% accurate and that radio waves travel straight through that large layer of charged particles called the ionosphere.. Try 20 meters.
If you want better than that, go differential.
But, back to the story of the GPS guiding airplanes, I feel inclined to bring out the fact that the airplanes still must use the existing altimeter as GPS is absolutely horrible at altitude. Considering that GPS assumes that the planet is one perfect ellipsoid, one can understand the range of error.
As for europe not wanting to base its airplanes on GPS, that makes perfect sense to me. The reason SA was turned off was because the DoD was able to demonstrate the ability of turning GPS on & off in specific regions. I would rather not like another country having control of whether or not my airplanes can tell where they are.
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Okay, so with this new system we're going to have pacman appearing on the screen? Jets telling other jets where they are? You're right, this is a James Bond flick waiting to happen! I can't wait to see what the evil guy with the nice hat will do when he finds out he just needs to "suggest" to the air traffic control system that none of the planes are where they're supposed to be anymore.
Indeed. I hat things that are har to undersand.
Never meant half of the things I said to you. So you know, there's a half that might be true - G. Phillips
The general rule of thumb for accuracy is that your lat/long will be about twice as accurate as your altitude. GPS receivers compute a figure of merit as to the expected accuracy of the solution- It is the residual of an over-determined set of linear equations. In general, the better the geometry of the SV (GPS satellite) constellation, the smaller your residual will be. The calculation of the altitude sucks because of the poor geometry of the calculation- you're trying to triangulate to a bunch of things essentially in the same plane, high above you (all in the +Z direction). You want to get some SVs in your calculation that are near the horizon, but the accuracy there will be off due to ionospheric differences, which is why the GPS system is a dual frequency system, the two frequencies give you ionospheric corrections. Unfortunately, no (commercial) handheld and only a few surverying receivers are dual frequency because only the Y code (encrypted P, or precise code) is on the second GPS frequency, and only the military has access to the crypto-keys for GPS. Some surveying receivers correlate between the two frequencies to determine the ionospheric correction factor, but this is not a trivial task: real time correlation between two 10 Mbit data streams.
But what I was trying to lead to- differential or or not, you're still working with the same basic constellation (no subterranean SVs yet), and your altitude will always be half as accurate as your lat/long.
What I'm unsure about is how much differential GPS helps out CA code receivers now that SA is turned off. With SA on, the effect was dramatic. For real precision, I don't know of any receivers that work well on a moving platform, since a large part of precision with a high quality CA code receiver is essentially just averaging. You have an inherent limit with a CA receiver since the raw code is a 1Mbit code.
Most of this is recollection from a seminar I took from Navetech about 3 years ago.
yes, but the handheld ones don't do it too accurately. I'd fire up my father's GPS, but I don't know where it is. I've seen the altitude reading off by 100 feet (I was out on the ocean, and it said -100 feet! I thought I was at sea level by definition!)
"Ancillary does not mean you get to rule the world." --U.S. Circuit Judge Harry Edwards, speaking to the FCC's lawyer
Hot spare's in the sky and on the ground maybe?
There are spares already up there, ready to be moved into the proper orbit when needed. GPS is a vital technology for the US military- they have lives depending on it already. What bothers me is the dependence on just one technology. Yeah use GPS, but have a backup (VFR?) ready for when something gets screwed up.
Well the earth isn't exactly round. Also the sea has variations in height just like land has, they're just not as pronounced as on land. Your father's handheld gps is probably a lot different from the differential gps the planes would use. normal gps is accurate to about 100 m (300ft), differential gps to about 10m.
Lans' system had an accuracy in the decimeter range (tenth of a yard) BEFORE the US DOD stopped fuzzying the GPS signal. This was achieved by a STDMA datalink (Self organising Time Division Multiple Access) and adding a few (there are currently around 30 of them covering Sweden, a country roughly the size of California) land-based transponder stations to the satellite coverage. The system basically use the land-based stations to enhance the satellite data. It is mature, operational and is an ITU and IMO world standard for large ships.
On the terrorist/security aspect, I'd just like to point out that all civilian and military aircraft are required to carry and operate radar transponders at all times while in 'civilian' airspace so this system doesn't change anything in that respect.
In short - it's a great system and everyone should use it; but it's hardly news.
This seems like a really bad idea to me. It's practically an engraved invitation to someone to modify or create a version of the GPS system that spews bad data into the network.
When will these guys figure out that you absolutely cannot, under any circumstances, trust externally supplied data. You cannot safely use any data from an outside source in your computations--and these guys are going to go and make our entire air infrastructure run on a trust model?
The mind boggles.
daniel
All I needed to know in life I learned from
DGPS is unnecessary especially in flight- It will get you to sub meter level accuracy, and that is far more accurate than I hope air traffic control will ever need. Airplanes (esp. the big ones) already have very good radar based altimiters/ground speed indicators that will get them better altitude and speed than GPS really has a hope for. There may be some use for DGPS for control on the taxiways, but realistically, they should be keeping much further apart than 10M, so it wouldn't make a significant difference.
These planes still have pilots, and they still and should have the final say over these technologies, especially when lives are at stake.
The article this refers to mentions nothing I can find about DGPS. DGPS would just make it more complex and vulernable to failure, both incidental and intentional.
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This was intended among other things to prevent the "terrorist" from making a "poor man's cruise missile" using a Cessna, a GPS, and an autopilot.
Only works so long as the "terrorist organisation" has no kamakazi pilots.
As best I can tell, we already do. One ATC operator could send a plane onto a collision course with another, and then there would be nothing to tell the planes not to. We implicitly trust the towers. If we do this, we just shift to a system that has DIFFERENT, but probably neither inherently more nor less, problems. The problems change from many potentially dishonest operators to very few operators, but many potential crackers. Navigation has had trusted client problems forever (lighthouses, whatever the land-based radio location system was, could all be messed with). I don't know of any recorded case of a problem. Admitedly, we have many more people who would want to mess things up, but I don't think that this is a new problem.
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Germany tried precisely this tactic when bombing London ...
That's not comparable. First of all, an full-blown airplane is a lot larger than a little 6-foot model. Second of all, this is not war we're talking about, but just a single target in the middle of city. The white house (or pick any other target) does is not going to have anti-aircraft guns at the ready.
120mph is chickenfeed.
That's 176 feet per second, or 2 miles/min. I guarantee you that if a little 6-8 foot model zoomed by 30 feet off the ground at that speed, you would not think it was chicken feed. Imagine me launching it from two miles away. 1 minute later it would hit the target.
do it with a ground-based tactical nuke (suicide, but effective).
Well, the point is the low-cost. The hard part would be to get lightweight explosives that would pack enough explosive power but would fit inside a model.
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Sometimes it's best to just let stupid people be stupid.
Obviously, you didn't read his comment close enough. He wasn't talking about human error. Right now, you have about as much logic as HAL-9000 did when he "reported" the error with the dish's PCB.
"Ancillary does not mean you get to rule the world." --U.S. Circuit Judge Harry Edwards, speaking to the FCC's lawyer
Not exactly. The Traffic Collision Avoidance System (TCAS) is an aircraft-to-aircraft system that works from a multitude of input data (as practically every on-board system does) to determine with the largest precision & accuracy the location of the airplane which is then broadcast out to other TCAS receivers in an attempt to avoid collisions.
Each TCAS receiver classifies incoming data in various levels: No Threat, Proximity, Traffic Alert, Response (?) Alert - which in aviation lingo translates to TAs (Traffic Alert) and RAs (Response Alert). The TAs and RAs are the only things of significance to the pilot since they are potential collisions (especially the RAs) - hence their color on the navigational and primary flight displays: yellow for TAs and red for RAs.
Based on his current flight (ascending, descending, level) the pilot keys in the TCAS system to show him only tracks of interest - if he's ascending, it makes no difference what's below him, etc.
This system is based on ground location data (from a multitude of sources, all based on radio towers located on the ground, with known positions) GPS data and differential GPS (where available - the only flight system I'm aware of that uses this in the US is the Boeing 777 with Honeywell's flight management computer (FMC) and Honeywell's large format display systems (LFDS) - similar to what was posted about the new shuttle display systems here on /. not too long ago.
Differential GPS is primarily only used for approaches, I believe - since that's the only time more precision than GPS is necessary (and even after the military scrambling of GPS ended, more precision is necessary to land the plane than military GPS provides) - 10 meter accuracy (or whatever it is exactly) puts you on the runway or off of it - not nearly enough for the autoland systems to feel comfortable with!
My reference: ex-avionics engineer for Rockwell Collins. That said, none of the statements made (express or implied) reflect the position, past or present, or presume to be 'expert advice' in any matters avionic, of Rockwell International Corp.
GPS is accurate to within 10-15meters with a hand held Garmin or Magellan, to get much better than 7m (autonomous) you need data from a ground based base station. (5mm is possible with a survey grade system, and a base station within 10km)
Europe is building their own system called Gallileo (deployment for 2005), Russia still has it's Glonass system flying. A major contractor for the European system is Novatel out of Calgary Canada (go figure)
In 2005 three more channels will be available from the next generation of American SV's so accuracies should improve.
GPS signals are difficult to but not impossible to fake. Most high grade receivers include anti-spoofing technologies to minimize this threat. it could be blocked but not easily faked
ADS-B is supplemental to exisiting radar systems, so it should improve exisitng navigation, as long as governments dont get lazy and give up on radar stations.
I don't know much about GPS in aviation, but I am a little surprised that this type of system does not already exisit.
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Not in altitude. From 18000 feet to 30000 feet (IIRC), the minimum allowable vertical separation between two aircraft traveling in opposite directions is 1000 feet. I don't know what the minimum allowable horizontal separation between two aircraft flying at the same altitude is, but it's at least a mile.
Since GPS is least accurate in measuring altitude, this might be an issue...
OK, let's think about this. The issue in question is supplanting radar with GPS. Apparently, you think that planes now get their altitude from the control tower. In fact, each plane has a device known as an altimeter. Miraculously, this device will continue to work even if GPS is installed in the plane.
Anyone read _Flare_ by Roger Zelazny and Thomas T. Thomas? One of the sub-stories describes how a jet nearly wipes out because it's GPS nav system is disrupted by a solar flare.
- This particular implementation is curently being tested in parts of Alaska where there is little to no radar coverage. While the system might not offer all the features of radar coverage, its a lot better than what's there now.
- All GPS's certified by the FAA for use in aircraft report altitude. In addition to use the GPS data to compute the altitude, many GPS units can also connect to the altimiter for altitude data just as MODE C transponders do now. Since selective availibility has been turned off, gps computed altitude is very accurate.
- Having the GPS report the aircraft's position for purposes of aircraft seperation is just one small part of this. The UPS technology allows for two way data tranmition between the aircraft and the ground. This is useful for uploding weather data to aircraft, something that is only currently available as an option on very high end corporate and commercial jets. The GPS simply says, "I'm here" and the bandwidth usage is minimized by only sending the data for the local area (as well as any pireps, sigmets, or other timely information). For what its worth, you can also check your email.
This system was never intended to replace ground based radar as a means for directing air traffic. While a single failed transponder can cause problems in the current system, a failed gps unit on a single aircraft in a GPS only system could be catostrophic.If you think this is cool, take a look at http://www.flightexplorer.com. it allows you to track flights in real time. Not just scheduled airliner traffic, but your friend in his Piper Cub.
I have a Garmin GPS III (not sure if the III+ acts identically), and I have held it to the window of an airliner. It nicely registers 525mph landspeed, along with a realtime map showing ground landmarks. Software copyright is 1997.
Civilian GPS units are not shielded from producing antenna echo, so turn it off when the nice crewmembers tell you to turn it off. In brief, receiving-only units like GPS need to amplify the weak incoming signals, and in non-aircraft units, some of the amplified signal leaks back out the antenna, which can interfere with other nearby sensitive devices like the airplane avionics.
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Or should we say it is *a* differential GPS. DGPS is a standard system that does not come close to the 8" or so accuracy of the Lans system. (The best i've ever seen with DGPS even since SA was turned off has been 3ft.)
Basically the lans system used DGPS data (diference in actual vs reported position from each bird) plus clock error data plus a higher density of differential stations. Of course this required expensive atomic clocks at each differential station and a very complicated (though not terribly expensive) reciever, but it certainly wasnt DGPS. And YES the US did try to supress installations of that system in this country as it took gps out of government control (e.g. if you lost satellite reception entirely, you could still possibly deduce your position from land-based recievers alone) where with DGPS you still had to have satellite communications.
~GoRK
I've often wondered how long it will be until someone puts a computer and a GPS into a remote controlled airplane, loads it up with explosives and sends it on its way. In the past, the accuracy of the GPS was probably too low, but I believe the current system is now 3 meter accuracy, which would probably be enough (along with some attitude sensors so it could stay level).
Or heck, make it a remote controlled jet! Imagine a 6-8 foot long jet travelling at 120-150 miles per hour aimed at the white house. It would be unstoppable.
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Sometimes it's best to just let stupid people be stupid.
Today, you can trivially override or jam the broadcasts from the air traffic controllers. This has happened and is considered a serious threat.
So setting up your own transmitter is just repeating an existing threat. The same techniques that are used to catch the folks jamming ATC will catch you.
Furthermore, since aircraft are most interested in signals from other aircraft close to them (which are the ones that represent a collision threat), your jamming would only be significant to aircraft very close to you.
So, overall, I think that the GPS autoreporting system can be significantly more jam-resistant than the current ATC system.
The only good weather is bad weather.
Sorry, but that answer doesn't cut it for me. Sure you can interfere with the existing air traffic control system with a cheap radio. Do you want to perpetuate this sort of vulnerability into perpetuity? If we're going to spend gazillions putting in a new system, how about we make it more secure than "it happens"?
For several reasons. First of all, on smaller aircraft, standard altimeters require constant attention from the pilot. The altimeter gets its data from comparing the pressure of the air outside the plane to the pressure of the air on the ground, and then doing some math to figure out the altitude. The problem is that the altimeter has to know what the pressure on the ground is. This is achieved through a small dial on the side of the altimeter that the pilot has to adjust every 15 minutes or so to keep it accurate. As you can imagine, this is prone to error, and added workload for the pilot.
Secondly, standard altimeters have a tendency to break. I've only been flying for a few years and have already run across several dead or dying altimeters that have required me to change my flight plans.
So I think GPS-based altitude (and this GPS system in general) is a long-needed treat for the aviation community. There are a few hurdles that need to be crossed, such as avoiding abuse of the system (I believe someone else already posted about this) and redundancy. But if they can get the flaws worked out of the system on the ground, I for one will be happy to fly with it in the air.
kugano
Also, as for getting rid of ATC's... They're like traffic cops. Without them, you'd have no way of resolving who gets to go where, when, in the cramped airspaces around a given airport.
Putting GPS on every airplane is a great idea for a bunch of reasons. For example, the black box could not just emit a pulse, but it could emit a pulse with its exact location. It will, in fact, make air travel somewhat safer. But it won't replace the need for towers, radar and controllers, and it's stupid to bill it as such. Just once, I'd like to see an article without hyperbole.
Having redundant base stations does you no good if somebody has set up some equipment to lie to them about what's really out there.
One thing most of those criticizing the GPS based system miss is that the current system greatly increases aircraft density, which itself leads to collisions. The Air Traffic System has fixed locations in the sky which aircraft must go to as part of standar approaches and departures. Furthermore there are fixed, narrow corridors. Thus many aircraft (especially small aircraft) are focussed into small parts of the airspace, and they do collide there!
With an autonomous system, without human controllers, such fixed points and routes would be unnecessary. Aircraft could go point-to-point, reducing density and collision probabilities. Furthermore it would increase traffic capabilities.
As a former pilot who had to spend way too much cockpit time dealing with air traffic control regulations and navigation, rather than watching for traffic and flying to a destination, I think that the current system sucks!
The only good weather is bad weather.
In this case, the stronger/closer signals are more important, and will reduce accidental jamming problems. The power at the antenna has to be similar, of course.
The system by itself does work best when all aircraft use the same system. It does not rule out other systems being used; an aircraft can also be monitoring existing systems or even optical monitoring.
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It can, since all you are really doing is just triangilating on another axis. Most of the low-end consumer devices can report alt., although the accuracy seems to vary from bad to not-so-bad. High end devices should be more likely to provide accurate alt. info, although it really depends on how many satellites are in "view" (the more the better).
I could see how GPS would be good enough to navigate by, but probably isn't good enough land by (yet).
Someday a Slashdot ID of 177180 will mean something.
Of course you sort of have to understand them since GPS is partly controlled by the American Ministary of Defense (or is that just a myth)?
But still superior technology should well be used.. Me thinks..
Ahhhh! Gnutella for Gnavigation!
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The fuzzy factor imposed by the US government to thwart military uses of their GPS system was lifted on May 1 of this year (see http://abcnews.go.com /sections/tech/dailynews/gps_000501.html) - making the use of GPS 10 times more accurate. So, GPS, even for folks like us, is now accurate to within 20 yards. Plus, airplance don't have too many things in their way to block signals from those satellites.
I think you picked the wrong James Bond movie - especially given that "Tomorrow Never Dies" plotline involved changing the syncing of the GPS satellites in order to send a ship into Chinese waters to start a war. Obviously some sixth sense working but only on half power :-)
Cheers,
Toby Haynes
Anything I post is strictly my own thoughts and doesn't necessarily have anything to do with the opinions of IBM.
Rather than imagining a conspiracy by the U.S. aerospace lobby to prevent a foreign technology from coming in (when, after all, consumers all over the US are already using an equivalent technology), realize that the vested interest against such a system is the air traffic control system, in the U.S the FAA. The FAA has, over the decades, significantly increased its air traffic control responsibilities, to the detriment of general aviation. They have a large bureaucratic fiefdom at stake here that they do not want to lose.
The only good weather is bad weather.
Even with radar, altitude has always been self-reported (Mode C). GPS civil mode will now have 20M accuracy, which is much better than ATC radar resolution in any dimension. But backups of some sort are always needed. For example, an Air Force ground test inadvertently took out all civil GPS for at least a few days, over upstate New York, as reported at the time by Aviation_Leak mag. It was rather diffcult to find the jammer, which was only emitting a couple of watts. Then again, as it now stands, the backup for ATC radar outages (whatever the cause) is verbal position reporting by radio.
Off-the-shelf commercial GPS does elevations too. Now that they've taken the dithering off the satellite signal, you can get high-accuracy elevations, not just to the degree needed to keep airplanes off the sides of mountains, but to land surveyor's accuracies, nice and fast.
My big fear is that this airplane guidance system seems to be distributed, so if the GPS system in one plane goes on the fritz, then all the other planes will think that one plane isn't where it is; you can see the danger in that.
Yours WDK - WKiernan@concentric.net
And if you're going to argue poverty of small aircraft, remember that right now most of those are invisible anyway. Those that don't have radar transponders aren't on most radar screens. They're bopping around on visual...of course, they're also down in the lower altitudes and away from the commercial aircraft.
i beleive what youre thinking of is that the government didnt allow the gps people to make it more accurate than a certain amount, but it can actually be accurate to like 3 meters, or something like that. the government also lowered the limit sometime in the past year i think.
A few things in the article leaves me with a few concerns over how expensive it'll be.
The first thing that concerns me is the ranges, 150 mile radius. That's roughly, 70 thousand square miles, how many planes can you get flying in that area? I'm not even going to consider how many you can get if you take into three dimensional space.
With this amount of space to monitor, and all those aircraft, you're going to need two things. The first you need is a fast computer to keep track of all these aircraft. Second you're going to need a damn good radio, and modulation techniques to have broadcasts between all those aircraft without having all the data garbled with collisions.
For the system to be effect you'd have to install it on all aircraft, how long is that going to take? Because if one aircraft, or even a handful of aircraft are flying through the area and only they and the air traffic controllers know about them, the main selling point behind this system isn't really worth while. You still need to rely on ground controllers to tell you who's out there.
For example, if a pilot relies in this system and sees a plane on a collision course, or near collision course, he might turn, into the path of another aircraft that isn't showing up on the system.
For the system to handle 150 mile radius, you need a powerful radio, or large antennas, (both of which you probably won't find in private planes). You'll also need to install it in military aircraft, remember the F-117 that buzzed the airliner a few weeks ago? This of course costs more money and more tax dollars.
I don't see how this system will be as effective as they're promising without it being installed in all aircraft that will be flying through an area. It will help, I'm not denying that, but it will not remove the need of ground controlers and their radars. It won't even lessen their need at all.
Software Engineer & Writer of Military Science Fiction and Fantasy Blog: petermwright.com Twitter: WrightPeterM
Waaaaait a minute, you mean that UPS is doing this? THE UPS? The "We run the tightest [l]ip in the s[l]ipping business" UPS? This is too funny. And they can't even track the location of a simple package!
Personally, I used USPS Priority Mail with the $0.35 tracking tag and insurance to ship my Western Digital drive for RMA.
"Ancillary does not mean you get to rule the world." --U.S. Circuit Judge Harry Edwards, speaking to the FCC's lawyer