HIRTA

[thing]

Whats the score on HIRTA's? I'm off up Whitby way on Monday and I can dogleg around Fylingdales 5nm radius HIRTA or go through it. (I'd like to fly up the NY Moors railway line.) All it says on the half mil note 3 is 'Aircraft should not remain for more than 1 minute within 1.5 nm radius of Fylingdales up to 8000 ft ALT'. You're not going to be in there for more than a minute anyway at cruising speed even if you fly right over the place. I know they can make GPS etc go titsup but I'll be visual with the coast. What's the consensus, OK to fly through (I might not even be in the 1.5 mile radius anyway) or dog leg it?

[Whopity]

Can't be any worse than putting your head in the Microwave!

[thing]

I suppose for the sake of an extra minute's flight time I may as well go around. Just wanted a look at Goathland and Grosmont.

[UV]

Depends on your aircraft's HIRTA rating compared with the HIRTA rating of the site.
As all light aircraft, that I know of,do not have a HIRTA rating, they can safely be overflown.
HIRTA's are a problem that affects fly-by-wire systems, contary to folklore about all sorts of other nasty biological things.

[Lima Juliet]

What you need is access to the classified HIRTA book that details aircraft succeptability and frequency/power. However, most don't and the CAA put WORST case on the charts. The comment on microwave ovens is deadly serious as some HIRTAs won't affect your aircraft but it won't do your soft and reproductive organs much good...

If I recall correctly, Fylingdales is one of those best avoided for the sake of your knackers/ovaries/liver/pamcreas/etc...

LJ

[24Carrot]

Wrap up well. I always use bacofoil.

[thing]

I'll get the tinfoil hat on then, thanks guys!

[snchater]

If HIRTAs were a significant problem then flying activity at Croft Farm/Defford and Hinton in the Hegdes would be difficult as both airfields are within HIRTA areas!

[IO540]

Just wrap some bacofoil around your g00lies

Or perhaps not; it might come in handy if your relationship is a bit rocky Or you want to conceive some 6-fingered kids, for Hollywood alien movies.

Seriously, I cannot believe the radiation from those sites could possibly endanger life. Some are laser sites, some are microwave communications sites. If they radiated something truly hazardous like e.g. 1 megawatt on a 1m diameter beam, the countryside would be covered in dead (probably fried) birds.

The hazards do exist e.g. I have two documented failures (both pitch servo burnouts) of my KFC225 autopilot over the same lat/long spot in France. As far as I was able to make enquiries, indirectly obviously, to the French military, there is "nothing there", but there is a danger area there with no special hazards marked. I guess it is a ground-air tracking (missile) radar and the crew are having a but of a laaff.

But with so many GA aircraft operating under little or no navigation, loads of people fly through these things, so they (in the UK anyway) cannot be that hazardous.

[cirrusdancer]

Remember the Darwin award for something similar

[Whopity]

Flyingdales transmits 800KW pulses between 420 and 450MHz into a 40db gain antenna. That's a high ERP.

[sunday driver]

Assuming these are parabolic antennae, does the inverse square law still apply?
If not, 800kW should set your bacofoil crackling.
SD

[Torque Tonight]

For military pilots HIRTAs are manadatory avoids with the avoidance criteria dependent on the the individual HIRTA and your aircraft type. Trials were undertaken to try to measure each aircraft type's susceptibility to each class of HIRTA. Odd effects on the aircraft were not unheard of in the vicinity of some HIRTAs and presumably odd effects on your body could be occuring that you won't get any master caution to warn you of.

I have often heard civvy pilots claim HIRTAs are no big deal. It may be true that they will fly through them for years and have no observable effects but I prefer to err on the side of caution based on previous experience, and will not be putting my crown jewels in the microwave. The often heard argument that 'if HIRTAs were really dangerous nobody would be allowed to drive cars within the circles on the map' is spurious as most of the HIRTAs direct their power skywards and not horizontally.

[mad_jock]

It would be quite silly though to go near one if you had a FADEC or electronic fuel controler or the like.

[englishal]

Rampisham HIRTA (BBC World Service) knocks out our Garmin 496 GPS regulaly if flying too close. It freezes and the only way to get it working again is to remove it from the panel, prize the battery out, inset battery and start again. Bit of a PITA when it is bumpy !

I worked this out because our GPS used to regularly fail on the way to Dunkerswell low level, exactly when passing Rampisham and no where else. At higher levels it was never a problem.

[24Carrot]

Assuming these are parabolic antennae, does the inverse square law still apply?

I believe so. A finite parabolic antenna will transmit most of its power into a cone. The cross sectional area of the cone increases with the square of the distance, so the power per unit area (within the cone) falls off as the inverse square.

[rans6andrew]

I would bimble on through in my aircraft (three axis microlight, Rotax with electronic ignition), without worrying. I have not been through there by air yet but I have transited the HIRTA just to the east of Portsmouth many times. I have yet to experience any equipment malfunctions in the area while using Acom radio, ANR headsets or Skymap GPS and either 2 stroke or 4 stroke Rotax'.

If the radiation was as bad for humans as some have suggested there would be a lot of fried walkers about, the Lyke Wake Walk passes through the area and is in line of sight for some distance. Also, I have been to the NYMR for the wartime weekend (October) many times and most years there has been a flying display (aerobatics) at Grosmont, Goathland or Newtondale performed by a Tiger Moth. Also, a chap in Goathland keeps a helicopter at his house, he must fly in the zone regularly.

Enjoy.

Rans6....

[BillieBob]

Assuming these are parabolic antennae,

They're not, they are solid state phased arrays with a total mean power output in the region of 2.5MW. Unlike the old mechanical dishes, which tended to concentrate transmissions to the north and east, the current arrays are electronically steerable through 360 degrees. Even though the main transmitted beam is set some 3 degrees above the horizontal, field strengths close to international safety limits have been measured on surrounding roads. I wouldn't choose to get too close to it in an aeroplane.

[sunday driver]

My antenna knowledge is clearly prehistoric.

A more considered question could be 'is the energy transmitted as a parallel beam, and if so does the inverse square law still apply?'

Stationary parallel beam = less probability of a zap?
No inverse square law = a big zap if it does hit?

SD

[IO540]

A parallel beam is a physical impossibility, especially at those wavelengths.

A phased array does not magically produce a parallel beam. Its main advantage is that the beam can be steered extremely fast, so multiple targets can be tracked concurrently.

As regards hazards to humans, this was done to death in the mobile phone debate. I am not aware of any credible study which found a hazard other than through the heating of tissue, and you need a lot of average power to do that.

A hazard to avionics is more real, especially the relatively flimsy and often badly wired (badly shielded, etc) GA avionics. The data I have on the KFC225 failures suggests that the frequent servo burnouts are caused both by internal and external RF emissions, but the totality of the failures I have had does not map onto published HIRTAs in any apparent way.