Thanks a lot for your answer. The aircraft was a standad production HS Comet 4 (1959). Let me add some more questions; always into the context of 1970's.
About the doppler;
Althought the doppler was not a mandatory equipment, it was then a common thing not to repair/replace this equipment? The doppler was out of action, at least, more than 10 days since de malfunction was detected. What is your opinion about?
About the VOR set;
-The aircraft was provided with duplicated Marconi AD 704/706 ILS/VOR, and the number 1 VOR set it has been repaired two times, because during the previous flights it was not working properly. The set it's replaced and seems to work properly. Apparently.
-One day after the VOR set number 1 was replaced, the aircraft was flying out of track without the knowledge of the crew. This is a fact.
My questions about;
-It was a mandatory thing to inform the crew that this equipment has been just replaced? In another words, they crew could be using the 1 VOR set without knowing anything about the previous malfunctions?
-It's a common thing to use both VOR equipments during the flight? Or if the crew trust in VOR set number one, because it seems to work properly, then they don't have any reason to use the second VOR set?
-It is possible that a malfunction in the VOR set mislead the crew, without any chance to detect that the equipment it's not working properly, and while they are convinced they are flying over/or in direction to a radiobeacon included in their flight plan, in fact they are flying over /or in direction to another radiobeacon not included in their flight plan?
-Apart from an eye contact with the aircraft on a radar screen, there was, by that time, another on the ground support that was able to determine the real position of the aircraft?