I wonder if the radalt on the Mk II was even actually approved as a navigation instrument at the time?
The RadAlt (AN/APN171) was one of the very few avionic systems cleared for use, but with restrictions.
These included a warning that crews should be aware of spurious indications when on-board radio transmitters were used. (Not that the intercom was cleared for use, which is somewhat of a limitation when flying an aircraft). And MoD have, apparently, lost the information on mobile phone and other personal devices carried by pax. Convenient.
Notably, the RTS omits the potentially serious combination of;
1. The Mk2 suffered power interrupts (reported by test pilots)
2. Power Interrupt testing on the RadAlt was detailed in the servicing instructions, but no suitable test equipment provided at 2nd or 3rd line.
MoD, again conveniently, cannot state what was being done about this failure, despite it being advised in (at least) 1983.