The preciseness of modern flight
UPDATE: I think John Glenn agrees with me when he says "going direct keeps the airplanes spread out more" toward the end of that video.
Reading a recent post on Philip Greenspun’s Weblog got me thinking about the pros and cons of VOR-based navigation vs. GPS.
I would argue with Philip in that, at least compared to VOR-based navigation, GPS would be less likely to cause a collision. The primary reason being that it creates the possibility for more "airways" than a pure VOR-based system does.
A little graphic shows this:
The yellow icons are VORs, the purple are airports.
With VOR-based airways planes going to different locations may have to cross the same point if they use the same VOR for their route. This is exacerbated if multiple VORs are being shared (purple line is overlapping course). However if each is on a direct route there would be, at most, one point where they would cross paths.
Even though the VOR airway may be 8 miles wide (because of the error inherent in VOR usage) the aircraft will still be very close when over and near the VOR.
Why is this? Well, if your VOR indication is off by 2 degrees to the left and the other guy’s is off a little to the left you will safely pass each other when you are in the middle of the airways, miles from each VOR. However, as you approach the VOR that 2 degree of error translates to much less distance across the ground – this means that the error in your VOR reading is no longer keeping you apart. If the timing is bad, you will both cross right over the VOR at the same time.
With GPS, there is less sharing of routes. Even aircraft going leaving an airport for the same destination may be on slightly different routes, since they might turn on a direct course from different locations after takeoff.
Another nice thing about direct routes - they let you spend a bit less time in the air. Beyond saving money on fuel, less time in the air means less exposure to mid-air collision.
With autopilots and precise positioning two planes given the same route and altitude are certainly more likely to be scraping paint than they would otherwise. But what comes with this precision is the ability to "make your own airway" and I feel that more than offsets the danger.
Maybe it’s because I’m a computer guy, but I feel that more precision is a good thing.
Reading a recent post on Philip Greenspun’s Weblog got me thinking about the pros and cons of VOR-based navigation vs. GPS.
I would argue with Philip in that, at least compared to VOR-based navigation, GPS would be less likely to cause a collision. The primary reason being that it creates the possibility for more "airways" than a pure VOR-based system does.
A little graphic shows this:
The yellow icons are VORs, the purple are airports.
With VOR-based airways planes going to different locations may have to cross the same point if they use the same VOR for their route. This is exacerbated if multiple VORs are being shared (purple line is overlapping course). However if each is on a direct route there would be, at most, one point where they would cross paths.
Even though the VOR airway may be 8 miles wide (because of the error inherent in VOR usage) the aircraft will still be very close when over and near the VOR.
Why is this? Well, if your VOR indication is off by 2 degrees to the left and the other guy’s is off a little to the left you will safely pass each other when you are in the middle of the airways, miles from each VOR. However, as you approach the VOR that 2 degree of error translates to much less distance across the ground – this means that the error in your VOR reading is no longer keeping you apart. If the timing is bad, you will both cross right over the VOR at the same time.
With GPS, there is less sharing of routes. Even aircraft going leaving an airport for the same destination may be on slightly different routes, since they might turn on a direct course from different locations after takeoff.
Another nice thing about direct routes - they let you spend a bit less time in the air. Beyond saving money on fuel, less time in the air means less exposure to mid-air collision.
With autopilots and precise positioning two planes given the same route and altitude are certainly more likely to be scraping paint than they would otherwise. But what comes with this precision is the ability to "make your own airway" and I feel that more than offsets the danger.
Maybe it’s because I’m a computer guy, but I feel that more precision is a good thing.
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