"Just to use GPS would be very foolhardy"
My airplanes approved to fly the North Atlantic just with 2 GPSes. Granted - no power lines there....
Anyhow, possibly you meant no pilot should use his DIY GPS approach ? That I would sign...
To split hairs further, visibility in Trier can be "measured" only by the pilot, nobody else. (unless there is an approved and calibrated VAISALA or the like installed)
Given the white I saw 1,5 hrs after the accident on Triers Webcam, the WX reports and the witness account - "we did not see the airplane but heard a jet noise and then a crash, it was very foggy" I´d say its save to assume the weather being very well below anything remotely close to VMC.
ATCwatcher hitted the nail on the head:
there were plenty on airfields open in full sunshine on the high terrain, all around Trier. Attempting yesterday to go inside the Mosel valley with this weather ( plus the fog was in icing conditions as well ) on a strip with no Nav aids is not understandable for me.
In this Video - at the very end - one can see the birds, pheasants, some of them in plastic bags. I guess we can discard the birdstrike theory....
Nach Flugzeugabsturz: Pilot hätte in Föhren nicht landen dürfen - Nachrichten :: Rheinland-Pfalz | SWR.de