'Cloudbreak' was a term in common RN ATC usage at Lossiemouth in the 1960s. Not sure if it was ever defined with precision in any publication, but it was certainly well understood by both aircrew and air traffickers.
It was used to describe a procedure for decent by RN, RAF and USAF (F4s and FIIIs) aircraft into LFAs 14, 15 and, for 2TAF Canberras, TainRange.
If memory serves me correctly, after a positive radar ident (turn or IFF), ATC issued a decent 'clearance' to a minimum safe quadrantal level based on the safety altitude within 100nm of Lossie and the RPS. I'm fairly certain that the term 'clearance' was used as part of the procedure.
In those days, RAF Canberras based in Germany flew direct to Tain Range, descended either VMC or under limited radar control or advisory service provided by both ‘Highland Radar’ (the GCI radar at RAF Buchan with a chinagraph GEOREF overlay) and ‘Moray Radar’ at Lossiemouth (with an electronically generated one), dropped the ordinance, enjoyed lunch at Lossie and returned to Germany in the afternoon.
In early January 1966, a 2TAF Canberra crashed into mountains west of Inverness whilst on a radar controlled descent into Tain during a ‘white out’ blizzard. Both the pilot and navigator were killed. Because of the weather, the wreckage wasn’t found for three days – and only then by a ground party. Aerial searches were impossible.
I recall that there was always a problem with visiting aircraft descending directly into TainRange or the then Low Flying Areas 14 and 15 because of the adjoining high terrain. The RN had installed 1960s state of the art radar at Lossie (I think it was the Marconi S264). My recollection is that the radar was as good as it got at that time. On the day of the accident, the Canberra was descending in IMC towards high ground west of Inverness under 'limited radar control' from Moray Radar. The decent clearance was, I think to an altitude below the minimum safe in a perceived expectation that the pilot would report VMC below and proceed VFR to the range. But on the day in question, there were snow blizzards and low cloud. In the prevailing 'white out' conditions (that were known to ATC), VMC below eluded the crew with fatal consequences.
Sounds familiar?
After the accident and subsequent CM of the RN air trafficker, the let down procedure for 2TAF aircraft into Tain was changed to a radar controlled decent for a GCA pickup to Lossie, preferably to runway 23 so that aircraft could let down over the North Sea, overshoot and then proceed VMC across the Moray Firth to the Range.
And a revised procedure was introduced for aircraft working Moray Radar, Moray Approach or Moray Director descending either into the LFAs or recovery to Lossie or Kinloss (including descents into Tain), that without exception, pilots were to be told that if not under positive radar control, they were responsible for terrain clearance, that they were descending towards high ground, that the minimum safe altitude/level was ....ft, and if they were IMC approaching that height/level, they were to climb immediately to the next higher quadrantal level and contact Moray Radar/Approach/Director on .....freq.
I'm not sure what happened to this procedure but it seems to have not survived the passage of time. And neither it seems have the dedicated landlines that in my day used to exist between Lossie, Leuchars and Buchan for handovers etc. Elgin Trunk Sub 4 rings a memory bell, as does the telephone network that each station was connected to via Prestwick.
It might be worth making some enquiries as to why the above process was discontinued; as this might go towards an argument that the Crown had constructive knowledge, and thus a duty of care which it then breached by not maintaining the above arrangements.