i have the following doubts on vor, any help would be appreciated.:
1. whats the difference between site error and propagation error?
2. accuracy of VOR is required to be +/-5degrees 95% of the time, then why do we have an index of 4degrees for the VOT (test vor) ?
3. does VOR not suffer from quandrantal error like the ADF?
4. does the failure warning flag come up when a/c is outside the coverage range?
kindly post explanations too.
11th Jan 2011, 18:46
1. Site error occurs because of electromagnetic conductivity properties around the transmitter (that is to say; magnetic fields, buildings, terrain etc etc around the VOR itself). This will be more or less constant over time, but may of course vary significantly on various radials. Propagation error adresses the propagation qualities of the signal, ie atmospheric conditions such as refraction, bending, scalloping etc. We know that electromagnetic waves are supposed to travel in straight lines, but various conditions affect this.
2. I'll leave that to someone else. I'm not sure.
3. The VOR does not suffer from quadrantal error. In fact, the quadrantal error has to do with the way the ADF (the on-board equipment) senses the relative bearing to the station -- so because the VOR reciever only recieves the the radial information based on phase difference, it does not compute a relative bearing (although it can be displayed on an RMI), and does as such not suffer from quadrantal error.
4. This would be equipment specific, but normally yes. The failure flag would normally be displayed anytime valid signal information is not recieved, for any reason.
11th Jan 2011, 23:47
The VOT tolerance is based on the accuracy of the VOT signal and the expected VOR receiver ability to resolve the test signal. It is completely separate issue from the inflight course line accuracy which includes such things as Flight Tecnical Error-- how accurately you and I can track the VOR signal, how accurate the signal is given conditions, tolerance of presentations, etc.
Yes, the flag will appear with an invalid signal, but that does not necessarily mean when the plane has flown past the service volume of the VOR. Fir example, a High VOR has a service volume of 230nm, but you will not get a flag at 231 nm. Coasting out overwater at FL450, it is common for the VOR and DME signal to stay until around 270 nm or so.