How harmful is Wx radar?

[difrips]

In our company SOP it says that, during taxi out, the Wx radar can be switched on when needed.

In reality this becomes a standard item during taxi, whereby almost everybody switches the radar on regardless of people, airplanes, vehicules, fuel tanks in front of them.

My question to you:

1) Wx radar is harmfull for human beings. What is the danger zone? 1m/5m/50m?

2) How bad is it to switch on the Wx radar when you have a large metal object (ie plane or fuel tank) in front of you? Can this damage the Wx radar itself?

3) What do most other companies do? Switch Wx radar on during taxi or when lining up?

4) Do the military still use civil wx radar beams to identify civilian traffic in sensititive zones (gulf region, Iran,...)


Thanks

[IRRenewal]

Health effects of exposure to radar microwaves (http://hps.org/publicinformation/ate/q315.html)

Not associated with them, just posting the link.

About the Health Physics Society

The Health Physics Society is a scientific and professional organization whose members specialize in occupational and environmental radiation safety.

[Captain Smithy]

1) Depends on how powerful the Antenna is. Most Antennae usually have a minimum safe distance where you will be OK from exposure. Most modern Wx Radars are very low-powered and have very close safe distances. I believe the safety issues are dealt with in the manuals???

2) No, because the metal reflects the transmission which will be received by the Radar as normal. If it's a high powered Antenna and you are close behind though you may get a little warm :) as may the occupants of the aircraft in front... as for the fuel tank however... :uhoh:

3) Not sure, I'm only an engineer, but I have heard that many switch on Tx when lining up for departure, others during taxi (there is another thread on this subject just now).

4) Don't know.

[Dani]

Most modern WX radars talk about 5m safety distance.

It might not be very dangerous but the energy emitted by the system is still far higher than any other source like communications (handphone, satellite, WLAN etc). So as long as we are not sure if these sources are dangerous, I would be somewhat cautious and don't use it beyond the manufactor limitation.

It is widely accepted that one only uses it in the air or lined up on a runway, sometimes already on taxiways when pointing away from ground handling personel.

Biggest misconception about radar emissions is that their radio waves are different to those "unhealthy" ones, like the radio activity (alpha, gamma particles). The later can be summed in your body and finally lead to cell destruction. Radio waves from radio emitters are different: They only are harmful if you get too much per time unit. They don't sum up in your body. You can compare it with your microwave oven: If you sit in front of it, your dosis is minimal, if you're inside, your body gets boiled.

Dani

[shanx]

I was just wondering ... is it safe to spot airplanes near the runway (landing and taking off) ??
(Is there any additional risk of contracting those harmful emissions if an aircraft on finals, flies directly overhead, say, at ~1000 - 1500 ft ?)

[ampclamp]

No.I dont believe you are in danger.(unless you are quite close) Modern wxr is relatively low power approx 100 watts I recall BUT the antennae are very directional which in short means that 100 watts ( for example) is effectively multiplied many times as its basically all in the one direction.
Output power is usually measured with an imaginary perfectly omni directional antenna called an isotropic radiator.

When that 100 w is fed into a modern plate (or any other directinal antenna) we use ERP or effective radiated power.
So you have a concentrated beam but it is very directional so if you are spotting you are still some distance away and as the plate scans you are not in the beam for extended periods.
With the inverse square law the power diminishes fairly quickly too.

I would say you are more at risk with the more powerful land based radars in operation around the fields.

I would think that minimising exposure to any high energy RF field is a good idea.More so the high end frequencies such as DME/ATC/TCAS then up to Rad Alt and then WXR which is a much shorter wavelength still.
They are not anywhere near the very short hi energy x ray band that can act at a cellular level. The jury is still out on what and how much damage is done but surely the less the better.

In answer to the one of the original questions it depends on the wxr used.ifyou are flying an old 727 or f28 for example you could be transmitting many thousands of watts thru someone. Not good.
"safe" distances on modern a/c are a matter of meters only but why take the risk.use it when you are clear of people and lining up would be sensible.You wont get a clear shot of anything until you clear the terminal and other reflective material anyway.
In the end vendor/company policy dictates but minimising exposure I think is wise.

[NSEU]

2) How bad is it to switch on the Wx radar when you have a large metal object (ie plane or fuel tank) in front of you? Can this damage the Wx radar itself?

It's not recommended, even though all modern radar receiver circuits have tunnel(?) diodes (or something similar) which prevent damage to the circuits when strong signals are received (from reflections and nearby radars).

[ampclamp]

Agreed.NSEU. It would be hard to envisage any tx/rx without rx front end protection. Reco not too regardless.

as for firing any radar at a fuel tank /tanker. If you do wear sunnies and ear muffs.Unlikely to blow but I would not be tempting fate too much.
Use of any hi power rf source is not a particularly good idea around fuel/ being fuelled etc.

[Captain Smithy]

I thought it was a given that you never transmit an RF signal in an explosive atmosphere (fuel vapours etc.), lest things go kaboomski :uhoh:

Captain S

[ampclamp]

yes capt I did understate that fact with a little humour.:eek:

[AerocatS2A]

difrips, this is what the Australian regulations say, I'd bet there are similar rules in your own country.

6 GROUND OPERATION OF AIRCRAFT RADAR EQUIPMENT

6.1 The requirement of this subsection shall apply to all radar equipment with a nominal peak power output rating in excess of 25 kW.

6.2 During all ground operation, including testing and maintenance of aircraft radar equipment, the operator and person in charge of such equipment shall ensure that:

6.2.1 The equipment is not energised in its normal mode (antenna rotating) unless the sector area scanned by the radar beam is clear of the following objects to a distance of 37 metres (120 ft) from the antenna:

(a) aircraft being refuelled or defuelled;
(b) fuel tankers, fuel tanks or fuel storage areas;
(c) persons or cargo;
(d) any other aircraft or aircraft hangar.

If you consider that the spacing between runway edge lights is normally 60 metres you'll realise that 37 metres isn't very far but it's probably unwise to just turn the thing on without thinking about what's around you. Our company procedure is to turn it on, if required, when entering the runway with the intention of taking off (ie. not when just crossing a runway.)

[con-pilot]

God I hope they are not harmful, not after over 40 years flying around in a radar filled environment.

[galaxy flyer]

Nr. 4 above.

Yes, there is an International NOTAM out advising civil operators in the Gulf and surrounding areas to operate weather radars continuously. Don't know about Afghan overflights, but probably not a bad idea.

GF

[Graybeard]

Arinc 700 radars, which began production in 1981, are less than 150 watts peak power, which is less than 1 watt rms, heating power. Your kitchen nuke is on the order of 750 watts rms.

If your old airliner's WX radar has a standby mode, then it is usually a high powered, pre-Arinc 700 radar. Only TWA kept the Standby mode when they transitioned to Arinc 700 radars, to minimize pilot training.

Have you ever thought about DME?

GB

[AerocatS2A]

Ah good point, hadn't considered that the weather radar is below 25kw.

[muduckace]

Most modern radar equipped do not transmit the amount of power as the older non-flat (convex) antennae did in the past.

[ampclamp]

I think I posted before most modern wxr's are 100 watts up the stick or so whereas the older gen stuff could be tens of thousands of watts and definitely will do some damage with extended/nearby exposure.

Also do not discount the ERP with 100 watts concentrated into a 3 degree lobe which will give you an effective radiation of thousands of watts, so be careful no matter what.

Last time I looked wxr was in the in the order of around 13 gigahertz.
Well above microwave ovens therefore much smaller wavelength at around 2 to 2.5 cm I think. Still much bigger than cellular level but still worth caution.

Someone mentioned DME .
Indeed, lower freq around a gigahertz but quite a hi peak power ~ 500watts.
Rad alt is around 4.3 gig If I remember correctly.Lower power but still up there in freq and I think worth avoiding where possible.

On the tarmac we are constantly being bombarded with all manner of RF signals.Some at close range.
I'm not convinced we are killing ourselves any quicker with RF and i think we have other more immediate OH&S issues like air quality and chemical exposure.I'm in the "less is likely better" camp.

Also I think some folks do confuse radio freq radiation with nuclear radiation. 2 different things altogether.

[radeng]

I doubt very much that any modern equipment uses tunnel diodes. Unlike other semiconductors, they have a limited life because of the very high doping density leading to further diffusion at room temperature.

The effects of RF are, as far is known and can be reproduced, limited to thermal effects. This means that the radar duty cycle (pulse length and time between pulses) comes into play, as does the length of time the exposure happens. For fuel ignition, there is a DEF STAN on the subject.

100 watts into a 20dB gain antenna gives 10kW ERP: however, there is only 100 watts available to heat somebody up.

[Mr Optimistic]

... after that its the eye humours which are most vulnerable I think so no worries !

[Graybeard]

radeng: 100 watts into a 20dB gain antenna gives 10kW ERP: however, there is only 100 watts available to heat somebody up.

That 100 watts is pulsed power, maximum of 1500 pulses per second, of about one microsecond width. 1,500/1,000,000 = 0.15% duty cycle = 0.15 watts average power. You probably generate that much electricity with your saliva.

Fearing modern radars is spitting in the wind.

GB

[radeng]

Graybeard,

Perhaps not 'modern', but years ago I worked on one that used a Travelling Wave Tube with 275kV on the collector, was 13 feet long, water cooled, and lived in a concrete pit lined with lead. Even with a .001% duty cycle, there was 5kW of RF, which would cook you!

When I did my radhaz course back in the '90s, we did an exercise on a 2MW S band radar of using a 'ball on a stick' to run along the waveguide looking for leaky joints. I found it was just as effective and quicker to run your hand along feeling for the spot where it was warm. A procedure heartily disapproved of officially by the lecturer!

Surprisingly, in pacemakers, where the battery power limits you to no more than 1mW out of the transmitter, you have to have some sort of small radome around the antenna to ensure you meet everybodies requirements on SAR. There we are talking generally of transmissions of a few seconds a month or less. becasue of battery life.

[ChristiaanJ]

Graybeard,

Can you elucidate on that 150mW average power for a radar with something in the order of 200 mi range?
Sounds like a misplaced decimal point somewhere.

CJ

[radeng]

ChristiaanJ,

Remember that we are talking of a 10kW ERP pulse, with 20dB receiver antenna gain - and in all probability, antenna gain is nearer 30dB. So a perfect reflection at 200 miles would be around the -83dBm level into the receiver, even though the average power is very low. Given the signal processing gain available, it doesn't seem too unreasonable.

[egbt]

Perhaps not 'modern', but years ago I worked on one that used a Travelling Wave Tube with 275kV on the collector, was 13 feet long, water cooled, and lived in a concrete pit lined with lead. Even with a .001% duty cycle, there was 5kW of RF, which would cook you!

When I did my radhaz course back in the '90s, we did an exercise on a 2MW S band radar

Try this one Type 85 air defence search radar (http://www.radarpages.co.uk/mob/linesman/type85.htm) 12 S Band trasmitters through one head each of 4.5 - 8 MW.

[Mr Optimistic]

http://www.ntsb.gov/Dockets/Aviation/DCA08MA076/403798.pdf

The following rules apply to the operation of aircraft radar equipment
while on the ground. In this context, "operation" means transmitting in
the "WX, TRB, TERR", position and does not include STBY, TEST, etc.
(1) Aircraft radar equipment shall not be operated while the aircraft is
being refueled.
(2) Aircraft radar equipment shall not be operated when another
aircraft, fuel truck, or other fueling equipment is within 50 feet
ahead or to either side of the nose.
(3) Aircraft radar equipment shall not be operated "nose on" to
another aircraft.
Note: Modem aircraft weather radar units typically transmit
about 70-80 watts of RF energy versus 50,000-75,000 watts
on older radars. The radar units in our aircraft fleet are
modern units, they do not pose a risk to humans, and they
comply with FAA Advisory Circular 20-68B. However,
despite safety to humans, it is prudent to comply with the
above restrictions to prevent possible damage to aircraft
equipment.

[ChristiaanJ]

Type 85 air defence search radar, 12 S Band trasmitters through one head each of 4.5 - 8 MW.Thanks, I'll be reading that in detail, seriously (always been a radar freak).
Does not sound like something I would have gone and stood in front of.

But at this moment I'm just trying to gather a bit of data again in the context of this particular thread.... which seems to ignore just about everything... peak power versus average power of the transmitter, antenna gain, the fact whether the antenna is scanning or not, beam width, you name it.

Unfortunately the internet seems to have very little coherent :) data.

CJ

[Piper19]

There is a saying among our engineers that standing for too long in a beam will cause you to have female children only. And in fact, 9 at 10 of them in my company have daughters, so maybe some truth in there? I'd rather believe you will not get any children at all:suspect:

[Dani]

slightly off topic. But you might be right. There is serious science trying to understand if it is possible to influence the gender of babies. There is one study that says that fathers with a sitting profession are more likely to have female babies, although not statistically significant. It might have a connection with the temperature of the father's sperm. Radar radiation might also induce higher temperatures.

As I said in an earlier post: microwave radiation doesn't work as radioactivity, so it doesn't primarly destroy the DNA, it just increases temperature in the affected tissue.

Dani

[radeng]

Way back when the world was young and the fields full of daisies and real beer was 1/3d a pint and even Watneys Red Barrel was palatable (yes it was - but they soon changed that!), radeng was an apprentice at Marconi in Chelmsford. It was noticeable and well known there that all the engineers working on high power transmitters always had daughters.

[MD83FO]

How many watts does an A320 radar utilize?

[pineteam]

Don’t know but they are completely safe. You can stand right in front of the radome with Radar on and it’s less dangerous as standing in front of a microwave.

[FlightDetent]

How many watts does an A320 radar utilize? According to the Aircraft Radio Station Licence


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wait for it...
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just a little
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110 W
160 W

two models that I got my hands on.

[vilas]

it’s less dangerous as standing in front of a microwave. Microwave doesn't transmit anything at you or outside, the radar beam will be directed at you if standing in front. So the comparison is incorrect. Radars have definitely become safer but if they don't cause any harm at all then why do the modern Aircraft still prevent you from using radar in dispersal?

[pineteam]

Hello Vilas,

I think this recommendations is just to be on the safe side as if we are not 100% sure it’s safe, then we must implement safety rules such as no cellphone during taxi and take off and landing. We all know this is horse **** but they still forbid us to use our phone.

For the weather radar, I know so cause I sent an Email to the manufacturer and they confirmed me it was not hazardous at all to humans.

Here’s the reply:

Hi Gregory,


Sorry for my slow reply. I recently retired from Rockwell Collins and now work contract for them. So I am not regularly checking my email. In the past, with very old weather radars, it was common practice to turn off the radar whenever there was no significant weather because you quickly wore out the magnetron. Today's digital radars no longer use magnetrons and have a very long life. So we recommend having the radar on from push back to taxi in. With that said, over time there will be wear and tear on the gears and bearings in the pedestal. And although Rockwell Collins has a very low failure rate for these components, they are a mechanical system and are subject to failure. So some airlines elect to keep the radar off during operations to reduce the mechanical wear and tear.

And I think this was mentioned in the Cathay video, but the radar is a very minuscule radiation hazard... less than standing in front of a micorwave oven. So it is safe to turn it on during taxi.

Sincerely,

Steve

[zoigberg]

Some blurb from Rockwell Collins on their Multiscan Radar (150W by the way)
“The American National Standards Institute has specified a maximum level of 10mw/cm^2 for personal exposure of 6 minutes or longer to radar antenna electromagnetic radiation. The exposure time is limited to the amount of time within the antenna pattern during each sweep.......Microwave ovens represent a more public safety concern and their leakage standard has been set at 4mw/cm^2. The WXR-2100 power density is half or less than that of the microwave oven standard.”

Which backs up what Pineteam is saying. Now I’m not going to lie down on a radome while the radar is switched on any time soon, but I will be pretty relaxed about whether I’m going to get fried if the radar happened to get left on.

As a general rule, a while ago I read 50ft avoidance should cover pretty much most of the radars out there today.

[wiedehopf]

Those distances are for being in front of the radar dish.
Isn't the more interesting figure how much radar energy there is in the cockpit from the weather radar? (none to speak of)

Also i get the impression people get confused mainly because it's "radiation".
Even without getting a sun burn, the light ("radiation" in the same sense as radar) from the sun will be much much more dangerous than the weather radar for pilots in the cockpit.

[ShyTorque]

The Wx radar in the aircraft I fly is wired through a weight-on-wheels switch so it doesn't actually transmit on the ground.

[Fursty Ferret]

No predictive windshear?

[ShyTorque]

No predictive windshear?

There's little or no problem with that in the type I fly, especially as it can fly at zero IAS. ;)

[Loose rivets]

The Wx radar in the aircraft I fly is wired through a weight-on-wheels switch so it doesn't actually transmit on the ground.

Hmm . . . I've squirted my beam up into threatening clouds before opening the taps on more than a few occasions. Often got useful returns.

Taxiing out at JSY and being stopped adjacent to the radar head. Bzzzzz Bzzzzz Bzzzzz on the headphones and even little movements on the old moving coil instruments. Vasectomy a waste of time on those nights. Nah, more than a few nippers given the spark of life thanks to that myth.

https://www.who.int/peh-emf/publications/facts/fs226/en/

[neilki]

PWS regularly triggers on the taxi out in Denver.... Honewell RDR 400. Its not kidding either....its on as soon as we move off the ramp...

[FlightDetent]

Another idea to consider: Are today's radars equipped with a safety guard against inadvertent operation on the ground in close presence of liveware? Or any health warning in the manuals? There is one on McD's coffee..

[pineteam]

Another idea to consider: Are today's radars equipped with a safety guard against inadvertent operation on the ground in close presence of liveware? Or any health warning in the manuals? There is one on McD's coffee..

Exactly. No safety guard or warning in case you forgot the radar after engine shutdown. As they know it’s not hazardous. If weather radar was dangerous, they would had have installed those safety features.

[vilas]

Exactly. No safety guard or warning in case you forgot the radar after engine shutdown. As they know it’s not hazardous. If weather radar was dangerous, they would had have installed those safety features.
The older generation radars weren't safe but still there were no safeguards. Only there was caution to the operator not to use it.

[pineteam]

True that master! :}

[Uplinker]

RADAR is an acronym: RAdio Detection And Ranging.

Some folk are nervous about (modern) weather RADAR - I have had pilots turn to me and say “ shall we turn the RADAR off to save our gonads?” People get freaked out by the terms ‘RADAR’ and ‘radiation’ and ‘beam’, possibly imagining something from their early comic reading and ‘death rays’ etc. All of this is bogus. Modern weather radar is low power, and the “radiation” is non ionising and is actually the same as visible light but at a lower frequency.

So think of a weather radar as simply a car headlight on high beam shining out in a series of short flashes, and a very very sensitive receiver looks for any reflections to that light during the gaps between the flashes.

Modern weather radar is low power: 100-150W has been quoted. The frequency used is around 10GHz, or 10,000,000,000 cycles per second, which is the resonant frequency of the water molecule, since water is what we want to detect.

Power of a transmitter reduces according to the inverse square law, so the power drops at 1 divided by distance squared, (sorry, I don’t know how to write equation format on this forum). So at a distance of 2 meters, the power received is 1/(2x2) = 1/4. So if the transmit power is 100 Watts, then at 2m it has already reduced to 25W. The equivalent car high-beam power has reduced to a car brake light power at 2m away from the aerial.

If you put your hand at the radar antenna, it might feel warm, similar as it would feel doing the same thing on your car with the lights on full beam. The only thing is that since the radar frequency resonates water molecules, unlike the car headlight, the weather radar could cause more heating in anything containing water, e.g. humans.

But, as I say, only about 100 Watts, so as long as you don’t put your eyes any closer than a couple of meters to the radar antenna, you should be safe.*

The problem with metalwork is that if part of the metalwork happens to be the same physical dimensions as the radar frequency wavelength then sparking might occur, which could be hazardous if fuel fumes are present. This is also why cellphones are prohibited at petrol stations - there is, (a very low risk that), sparking caused by cellphone transmissions could ignite petrol fumes.

Back in the cockpit, those pilots who worry about the weather radar affecting their gonads are behind the radar antenna, which is simply a reflector - like a mirror, so probably no radar waves reach us at all.

Since the radio output of a radar is focussed into a “beam” some say it magnifies the power. It doesn’t. The power remains the same, but the energy is focussed in one direction compared with an omnidirectional antenna. And the “beam” is not pencil like as in a l@ser beam; it is relatively wide, about 30cm diameter, and remember the reduction of power with distance. The safety exposure limit for skin is 10mW per sq centimetre.

* I am much more careful about not looking into a microwave oven - 750 W only 10cm away from your eyes is much much more dangerous. I stay well back, and don’t rely on the microwave oven RF shielding to protect me.