Thank you all for your answers.
My questions are related with the report of the Dan Air Comet 4 G-APDN accident near Barcelona (1970). I became interested in this case, because from time to time, I go for a walk in the mountain, and sometimes a walk near the place of the accident. There is not so much information about it. Several months ago I find the report (it's on gov.uk), and I read it, several times because, obviously I wasn't able to understant anything. My questions are about things explained on the report.
The “doppler out of action (allowable)” and the “1 VOR set” which was replaced because of previous malfunctions are mentioned at the beginning of the report, and I wanted to understand a little bit what they are; just because in the “conclusion and propable causes” they said “they aircraft displacement to east could have come as a result of some defect of the aircraft equipment”. But they did not point specifically to any equipment.
I have another question.
They say the cause of the accident was a combination of “erroneous information regarding reporting points, together with the existence of a radar echo coinciding with the report from the aircraft of passing that reporting point” (an echo with characteristics similar to those which the Comet should produce in terms of direction and speed). But they did not point to any kind of explanation/hypohesis about what this false echo was. The report say the radar was working properly.
(Into the context of 1970)
What do you think about?
Is a false echo a common thing?
Any hipothesis?