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GPS jamming -
Wouldn't doubt it for one minute. Regular event in the eastern Mediterranean.
Years ago it was suggested there was a GPS jammer on every 'telegraph pole' across mother russia. Leaves them with Glonass unfettered.
From the linked article ......
“Flying is still safe. Airlines have operational procedures for such situations if the GPS signal is lost,”
The problem is not so much when the GPS signal is lost, but when the signal is spoofed - meaning - you still get a recognisable signal and therefore no warning, but it puts you somewhere else ... ie, it tells you that you are where you think you are -
but you ain't .... 
LFH
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