An aircraft is flying over water towards a VOR/DME station. When the pilots are approaching the station, the warning flag on their CDI pops up. What is the reason for that?
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A
The receiver in your aircraft senses that the values are wrong, that is why it shows an error flag.
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B
The ground station measures that the indications exceed certain limits and shuts them down.
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C
Skywaves and ground waves interfere and cancel themselves.
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D
The wrong VOR frequency has been tuned in.
062.02.03.01.09: State that failure of the VOR station to stay within the required limits can cause the removal of identification and navigation components from the carrier or radiation to cease.
When the warning flag on a VOR/DME CDI (Course Deviation Indicator) pops up, it indicates that the ground station has detected a problem with the signals being received by the aircraft. The VOR/DME ground station continuously monitors the signals it is transmitting, and if it detects that the signals are being received out of tolerance, it sends a flag to the aircraft warning the pilots that the signals may be unreliable.
"The receiver in your aircraft senses that the values are wrong, that is why it shows an error flag." is incorrect because the receiver in the aircraft is not responsible for displaying the warning flag. It is simply receiving and displaying the signals it is receiving from the ground station.
VOR automatic self-monitoring system
The monitoring system gives a warning if there is the following:
- Change in bearing in excess of 1°.
- Reduction of more than 15% in the signal strength of the carrier or modulated components.
- Failure of the monitor itself.
Should any of the above cases occur, the identification and the navigation signals may be removed or the VOR signal radiation may cease. In this case, the onboard equipment will show a warning flag
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