[chevvron]

Why do people assume that that the danger is overhead these sites?

Because that's what a circular area with a height restriction suggests! What else should be assumed?

It was changed from a semi-circle in about 1980, but in fact, the radiation hazard only exists south of the east-west median due to the fact it communicates with geo-stationary satellites over the equator and there's no hazard to the north (according to the UK Mil AIP).

[kanga]

.. in fact, the radiation hazard only exists south of the east-west median due to the fact it communicates with geo-stationary satellites over the equator ...

that may be true of Oakhanger (at the moment) but may not be true of other HIRTAs ..

[Keef]

Unless you look up the details, you can't be sure. Even then, there may be other things in those domes that aren't talked about and which squirt in a different direction.

There aren't many that push out enough RF to be dangerous to people (anyone remember Cobra Mist?), but they might give your COM, NAV, or GPS a headache. Whether a permanent or a temporary headache will depend again, but permanent damage is pretty unlikely.

[chevvron]

.. in fact, the radiation hazard only exists south of the east-west median due to the fact it communicates with geo-stationary satellites over the equator ...

that may be true of Oakhanger (at the moment) but may not be true of other HIRTAs ..

Sorry I should have said I was referring to Oakhanger. The notification of it in the Mil AIP is quite specific and there's a list of other HIRTA's which, although depicted as a circle, are 'safe' in some quadrants even to aircraft with FADEC systems like Chinooks. I don't have access to this document any more, so I can't be more specific.
I was told when I first arrived at Farnborough that nobody used to take much notice of Oakhanger until one day, a Farnborough based Wessex with flotation bags (which were triggered electronically) flew through and the flotation bags were triggered. Investigations revealed the cause was the electromagnetic power of the signal being radiated, hence HIRTAs were born.

[Dave Phillips]

The Mil AIP used to list the 'type' of threat. There was then a list somewhere (could have been AIP or more likely GASOs as the information was rather sensitive - don't want Ivan knowing how to zap your aircraft) which specified what threats particular aircraft types and 'fit' could tolerate. I recollect that some aircraft types (Tornado GR1 springs to mind) had a rather comprehensive matrix of "do nots".

[chevvron]

We had a 'new' radhaz avoid marked on our video maps at Farnborough about 5nm east and in the runway 25 pattern when Tornados began to visit. We had to keep Tornados (and the FBW Jaguar) at least 2nm away from this position. Years later, I asked if we still did; our chief techy enquired and was told it had been a 'receive only' (and hence no longer a hazard) station for about 10 years!!

[joe-fbs]

So aircraft designed to operate in the likely nuclear environment of a 1980s war in Europe were not hard against EM damage?

[Dave W]

Oh, they were. I suspect that in the first instance the aim was to "simply" survive a massive nuclear Electro-Magnetic Pulse, whereas the other case is for all equipment to continue operating under a radiofrequency environment - i.e. the two can't really be compared.

The 1980s saw unexpected effects on contemporary avionic systems due to external RF - including the loss of a Tornado GR Mk1 in Germany attributed to RF from a transmitter mast, as well as the potential triggering of Electrically-initiated Explosive Devices (EEDs) such as engine fire bottles, hoist cable cutters and (as chevvron says) emergency flotation gear. The effect of events such as those was much greater design and test & evaluation emphasis on EMC/EMI, which unsurprisingly continues up to today. The information that Dave P describes is still produced for UK military aircraft.

At Boscombe Down there is an area known as "The REG" (radiofrequency environment generator) with many transmitters and calibrated systems to enable assessment of aircraft at least up to A330/Voyager size. That's the biggest in the UK, but several other similar facilities exist.

[G4UMW]

anyone remember Cobra Mist?

Yes! It caused significant disruption to communications in the 1.6-3.8 MHz marine R/T band along the East Anglian coast, including the 2182kHz distress frequency. The navigation warning that was promulgated while the station was active warned amongst other things of the possibility of "sparking in the rigging". Peak power of the station was around 10MW.

[Dave W]

I didn't know about Cobra Mist so went a-Googling.

Fascinating; one thing I found which may be of interest to thse who understand more about radar than I do is this declassified report from the late 70s.

(We're getting a long way off topic for a Red Tape & Gold Plate thread, though.)

[Keef]

We are horribly off-topic, aren't we!
I have a book about Cobra Mist and the other skulduggery that went on at Orfordness. All gone now, and it's returned to the wildlife.

[G4UMW]

My in-laws live in Snape which is not a million miles from Orfordness. There were stories (probably apocryphal) of locals getting shocks from RF-induced volts when they touched anything metallic, including cutlery. The site was later used by the BBC for a World Service transmitter. The BBC masts are still there but I don't know if they are still used.

Apologies for further thread drift!

[chevvron]

I believe RAF Bawdsey was near Orford Ness too. It was an air defence radar unit.

[G4UMW]

Indeed it was, and a Bloodhound missile site too.

[rohmer]

I recently heard about some kit in a Lynx being fried after overflying Rampisham in Dorset. I've advised NATS (& the CAA) that this site, which had been run by Babcocks as a short wave transmitter for the BBC World Service, had been sold to British Renewables over a year ago, the masts have been dismantled and it's being turned into a solar farm. But because an Ofcom licence still exists for it, it's still on the charts.