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Tune Identify Test - Glass Cockpit
G'day
I'm hoping someone with a bit of knowledge can clear up a debate that I have been having with a few colleagues. When tuning identifying and testing a VOR, the convention is to spin the course to note deflection of the CDI. In a glass cockpit is this a necessary process? Would the system not just display its fail flag? Cheers |
Most glass will automatically identify the VOR anyway and display its ident.
We have no requirement to listen to an ident. |
The OP isn't talking about identing the VOR, they are talking about testing it's serviceability by varying the course, and seeing the course bar behave appropriately.
The VOR works by running a phase comparison between the reference signal and a variable signal. The warning flag usually appears when no signal is received (either reference or variable signal), or when the one received is too weak, and also monitors the receiver itself and will appear if the receiver or indicator is malfunctioning. There are a couple of rare failure modes which can result in no flag, and an apparently valid signal, however: http://www.pprune.org/private-flying...lure-mode.html
Originally Posted by IO540
The point is that the circuits driving the bar, the t/f flags, and the Invalid flags, are all substantially separate, and can thus fail separately. This is how it has been since day 1.
If this is a certification issue then VORs and NDBs and ILSs will be shut down too :) I wrote it as a heads-up (as the Americans call it) because the flight training system maintains that if the Invalid flag is not showing, the instrument can be trusted, which is bollox. |
G'Day jpilotj
In a glass cockpit is this a necessary process? Modern receivers will also have BITE (built in test equipment). |
Most glass will automatically identify the VOR anyway and display its ident. This is not an assumption you should make. As a VOR does not transmit an electronic ident only systems that can decode morse will id a VOR. DME do transmit id and often systems will display the DME ident. |
On our glass display, the VOR needle doesn't get "generated" and point to the beacon unless the needle works correctly. The "ident" letters are shown on the GNS530 side bar. I still check the Morse IDs aurally to confirm both the VOR and DME. If using the beacon to track (not often needed as we don't fly airways) I would confirm the beam bar worked in the correct sense as a function of setting the course pointer.
Whether or not I need to do all this these days, it helps stop me getting bored when I can't see much out of the window. :oh: |
FE hoppy,
good observation, Rockwell Proline 21 works that way, only DME beacons are identified and displayed......VOR ? you do it the old fashion way. |
rudderrudderrat, thank you. I thought this might be the case with the old style systems.
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None of these checks are conclusive. See this.
Turning the OBS and checking for the correct deviation bar movement just tests one part of the circuit. Listening to the morse code checks a different part of the circuit. But there is no test which checks everything is working. You could still have e.g. a blind spot (caused by e.g. a broken antenna or antenna cable) which won't show up until you find yourself in the "right" place on the approach and then you get the incorrect instrument indication. EHSI/EFIS based systems are less likely to suffer from any individual problem because most of them decode the composite signal in software, which will either all work or all not work. But nothing protects from the broken antenna/cable problem which can be detected only by somebody with an avionics tester walking all the way round the aircraft and measuring the dropout signal level on each of a number of bearings. Or by flying to a good distance from a VOR and doing an orbit. |
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