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BYOD
21st Apr 2004, 07:16
Crossing the pond with a bloke 1 mile in front and 1000 ft below. Must have been fried by my radar by the time we crossed. Hope he was shielded by that aluminium tube. Any comments bout this from techkies?

A and C
21st Apr 2004, 07:45
At that range the "microwave" effect of your radar is not a problem to do any damage a person would have to be within about 50 feet ( if my memory serves me correctly ).

However I am told that the BA ground engineers at LHR "killed" a police radar speed gun that was being used on the ramp by giving it one or two sweeps of the WX radar from a 757.
I can only think that the gun was looking for an RF return of about 0.075W and got 200W from the 757 !.

Daysleeper
21st Apr 2004, 08:20
http://hps.org/publicinformation/ate/q315.html

In short its not a problem beyond 10 feet.

Rollingthunder
21st Apr 2004, 08:23
Had a B737 in dock on a C check once. Avionics guys were working on the radar. It was on. Unfortunately a lead was working on the dock in front of the aircraft. The radome blocked their view. She was exposed to it for around an hour.

She spent quite a time in hospital and many months off work afterwards and took a couple of years to fully recover.

Procedures were changed after that.

radeng
21st Apr 2004, 09:58
If we assume the radiated power is 50,000 watts, I make the power the guy would get standing there as 1/30 millionth of what he could get from a microwave oven operating at the maximum allowed end of life leakage.

However, how much more cosmic radiation he got from flying at 30,000 or so feet than being on the ground is another matter......especially as the aluminium tube doesn't do much to stop that!

Flight Detent
21st Apr 2004, 11:11
Hi all,

Then I'm wondering why our Ops manual for the B737-700 tells me the safe distance for the WX radar, in the full 180 degree forward arc, is 275 feet!

Cheers

ukeng
21st Apr 2004, 11:41
Probably because your aircraft is US built, they tend to err on the side of safety to avoid any lawsuits. Note the number of decals around the aircraft stating the obvious.
My particular favorite is the one on the inside of the DV window frame on a 757 which says "Window open"! :)

Can't comment on the damage done by the radar other than we never stand in front of them when it's on and NEVER use it inside the hangar. Same goes for HF transmissions.

radeng
21st Apr 2004, 14:09
Flight Detent says:

>Then I'm wondering why our Ops manual for the B737-700 tells me the safe distance for the WX radar, >in the full 180 degree forward arc, is 275 feet!

I'm not sure what the effective radiated power is for a weather radar - I assumed 50,000 watts. On that basis, if we assume the standard saftey level of 1mW/sq.cm (10 watts/sq. metre), then at 275 feet, the power is 0.566 watts/sq. metre.

That takes no account of the fact that you have to take average, not peak power into account (that drops the effective power by the duty cycle) and for radhaz work, you also integrate the total exposure over 6 minutes.

It's still not a good idea to get too close though. When I did the radhaz course, there was an exercise to find leaks in the waveguide of a 2 MW radar transmitter (the radiated power was much higher): I found them faster by running a hand along the waveguide and feeling for the warm place than was managed with the proper intrumentation. Not really recommended!

The eyes are the first things to go, by the way......

ramsrc
21st Apr 2004, 15:00
I found them faster by running a hand along the waveguide and feeling for the warm place than was managed with the proper intrumentation

Heard of a bloke who managed to burn a hole in his hand doing that regularly, over a prolonged period. Doesn't do the tissue much good in the long run.

Well thats Me
21st Apr 2004, 23:53
Well mate it depends what your flying, RADAR technology has come on leaps and bounds,if your flying a glass cockpit ship you could be sat in front of the radome for 5 mins without any harm,if its a unmodified older generation ship then i wouldnt like that 5 minutes unless your one of these guys that hates kids anyway!

Fragman88
22nd Apr 2004, 02:09
Many moons ago read a story (maybe Urban Myth) about a US pilot having severe headaches, followed by sight loss. Subsequently he recalled having been standing chatting for a significant period, leaning on the radome of of his A/C (I heard DC9 but must have been a low set nose!), and then boarding to find the radar ahd been left on. When his problems developed, he was told due to the Frq/Wavlelntgh of the radar (approx 3 Cm), there were four organs in the body of a size susceptible to microwave-style heating and tissue damage (dipole effect or somesuch) , two of which were his eyeballs!

Good to stay away from.:sad:

B737NG
22nd Apr 2004, 04:37
Ha ha ha that can only happen to a UK Cop (Bobby)....
law enforcement on the ramp. I hope he is prepared to
take all the radiation and emission on the ramp during his
duty. Poor bloke, he better seeks a transfer to the greens...

NG

SimJock
22nd Apr 2004, 06:52
You would think that someone would incorporate a safety circuit into the radar system that dumps the radar tx signal when the aircraft is on the squat switches.. is it too late to patent this idea ?

oh yes.. it is now :(

Scottie
22nd Apr 2004, 07:39
Simjock,

Would be a good idea however we need the wx radar on to look at the departure path before take off to check for CB's etc.

The 737NG and I assume others have a predictive windshear system which utilises the wx radar on the ground during the initial part of the take off roll to check for windshear.

Lear_doctor
22nd Apr 2004, 08:37
Already been done SimJock I'm afraid. Some business jets (the Cessna 560 to name one) already have TX inhibited on the ground.

No large bag of cash for this idea, looks like you will have to continue in your current employment for a little longer!! :O


Regards


The Doc

SimJock
22nd Apr 2004, 20:38
Ahhh.. OK then, I'll settle for a system that switches off with the engines then.. that suit ?

Lear_doctor
23rd Apr 2004, 07:53
Yes I think it would. I hope you will remember the little pepole when your rich. :O

All the best

The Doc

Le-Slat Disagree
24th Apr 2004, 19:07
WX radar off on engine shutdown????

Poor marshaller..... might make his bat's glow at night if his batteries fail though....????!!! Maybe something else too......!

Le-Slat

superpilut
24th Apr 2004, 20:00
ehm... couple it with the squats AND the flaps perhaps?

GND+flaps 0 -> radar off
GND+flaps whatever -> radar useable
FLT+ flaps 0 -> radar useable

No takeoff without flaps and after landing you anyway select them up!

SHOW ME THE MONEY!:} :}

(maybe it can buy me a course in learning to write proper English, so I don't have to edit for typo's the whole time:hmm: )

Inflight BBQ's
30th Apr 2004, 00:50
Hi guys,

I'm a purser with Domestic carrier. Quite often I will enter the flight deck before departure and chat to the tech-crew during boarding.

On more than a few occasions I have noticed the WX radar sweeping along merrilly and displaying a nice solid bank of buildings in front of us. Is this the sort of stuff infertility and eyesight-loss is made of?

Just asking, because when I'm downstairs dropping off my o/night bag, I want to know if I should just leave it that little bit further away...

Cheers :ok:

compressor stall
30th Apr 2004, 01:19
PC12 has a ground inhibit too, but we disable it so we can get a scan before take off. Useful on a dark stromy night in the middle of nowhere.:ok:

wheelchock
30th Apr 2004, 01:22
Inflight BBQ's,

When maintenance has the wx radar turned on on ground, it's most probabaly in test mode. I fly an old piece of junk with an AVQ10 wx radar, with that in test mode, it basically only tests the screen, not the TX. I wouldn't worry about it too much, but would avoid walking in front of the nose dome....I don't know what the test mode does on newer generation airplanes/wx radars.

I don't agree with having the wx radar off on the ground. Reason for that (call me nuts) is that on our old system it actually scares off the birds on the runway. If we depart from a runway with birds around it, we usually leave the thing on. Believe it or not, but they all disapear off the runway.

bigbeerbelly
30th Apr 2004, 13:34
I think superpilut makes the best point about inhibiting the wx radar on the ground. Linking the radar to the ground proximity sensors and the flaps is the only way that this could be acceptable. Once, back in the day while flying the J32 I was number 7 in line for takeoff and the airport was on a ground stop because of storms within the boundary. Tower calls us up and says if you guys want to depart first you can be the "pathfinder". From our perspective, the wx did not look that bad so we said sure. Once on the runway with the radar turned on and tilted up, we quickly realised why we were given priority over the heavies. (19 pax vs. 200+). I'll think twice about being a pathfinder in the future.

unruly
30th Apr 2004, 15:54
Ground inhibit for the radar? That's just making a simple problem complicated. Why not just put it on the checklist (in BOLD letters) so that it won't be forgotten? Then make it company policy for whoever forgets to be subjected to 10 minutes exposure infront so he/she will not do it again! :O

Max Angle
30th Apr 2004, 16:38
On more than a few occasions I have noticed the WX radar sweeping along merrilly and displaying a nice solid bank of buildings in front of us. Not sure what a/c you are talking about but it's more than likely the Enhanced groung proximity warning. It paints on the screen using the same system as the weather radar and can be confused for it, to avoid confusion on Airbus at any rate, it sweeps from the centre outwards rather than side to side. Unlike the radar there is no transmission taking place. Ask the crew next time and I am sure they will explain it to you (or switch the radar off in an embarrassed hurry if you are correct!)

EFP058
30th Apr 2004, 16:47
No takeoff without flaps
Have you told the Fokker 100 and Airbus A310 crews about this? ;)

ex jump pilot
1st May 2004, 13:42
Someone wrote "I'm not sure what the effective radiated power is for a weather radar - I assumed 50,000 watts" and continued "When I did the radhaz course, there was an exercise to find leaks in the waveguide of a 2 MW radar transmitter (the radiated power was much higher)"

Small point. Radar sets of this sort send out a pulse of energy then go quiet. That's because the radar set waits to see what comes back - which is of course a reflected pulse of radio energy from the storm cell (or hanger...).

If a radar set was emitting 50Kw of effective energy, think about the efficency of the radar transmitter. Say 50%? Then you'd need 100Kw of input energy with the other 50% appearing as heat. Is that a reasonable amount of power to obtain from the aircraft's generators? On that basis of efficency, a radar set of 2Mw (that's megawatts) would probably require a small ground based power station to run it...

Main point being a radar set can be thought of as a sophisticated microwave oven hence don't get very close to the radome when the radar is running. The effect of the weather radar on people is the same as that of (if you could) putting your body inside a working microwave oven. As a side effect, overcoming the safety switch on a microwave oven so that it works with the door open means that you have a nifty radar jammer which has be known to fool guided missiles...but don't stand beside the oven when doing this in a war zone.

radeng
3rd May 2004, 11:01
ex jump pilot,

When talking about the power of a radar, it's customary to be talking of the peak power during the pulse. The average power is much less - by the duty cycle.

Assume you want to see out to 40km. That means the time between pulses is a minimum of 266microseconds. If you want resolution to 300 metres, the maximum pulse length is 1 microsecond. This gives a duty cycle of 1/266 or .00375. So a radar giving 50kW peak at the transmitter would actually be only 187.5 watts average.

I also said 'effective radiated power'. This is the power of the transmitter multiplied by the gain of the antenna. A 2 foot dish at 5Ghz will give around 20dB, so my example of the 50kW ERP is actually 500 watts (peak) of RF, and with a duty cycle of .00375, is only a few watts. In all probability, a magnetron based thing will run at around 20 or so watts average, and quite likely around 20kW peak. So the power requirements are well within the aircraft generator capabilities - unlike the start of WW2, where things like Whitleys and Blenheims reportedly had only about 500 watts for everything!

I agree that it's not a good idea to stand in front of one while it's working, though. Incidentally, although it's never as far as I know been formally studied, it is apparently well known amongst engineers working on high power microwave transmitters that when they father children, it's almost always daughters........

Sonic Bam
3rd May 2004, 13:56
Ok, interest piqued so had to look up some figs for this.

Radar safe distance is Max Permitted Exposure Level (MPEL). MPEL is a function of antenna/dish diameter, rated peak power output and duty cycle (time from start of one pulse to start of next pulse transmitted) - radeng explains a lot of this.

The American National Standards Institute (ANSI) gives an MPEL of 0.005 Watts per square centimetre though other national standards of 10mW/cm squared are sometimes used.

Old weather radar sets had to transmit high power because the receiving processor electronics were noisey and needed a higher power return to be able to show a picture of the weather. This isn't the case anymore. Some of the power outputs quoted above would do an Air Intercept radar on an F15 proud.

With newer, more sensitive processing electronics, a good return for showing weather can be of a much lower strength so the transmitter power can be a lot lower.

Transmitted power outputs on modern weather radars range from 1,300 watts (1.3kW) to 10kW giving Radar Safe Distances of 2.7ft for the Bendix RDS-86 fitted to the BAe ATP to 13ft for the Honeywell RDR-4B on large Boeings and Airbus.

So to answer the original post's question - the plane in front was quite safe.

Rule is though, don't switch the thing to transmit until you are taxiing out. Some aircraft have system disables installed but the pilot is the best controller of all.

Sorry you asked now?

ex jump pilot
3rd May 2004, 17:25
Sorry you asked now?
Not at all. Thank you everyone who added to the debate. I was a bit unclear how the 'power' went from "50kW ERP is actually 500 watts (peak) of RF, and with a duty cycle of .00375, is only a few watts". Now I know.
Doesn't take much power to reach the upper advised limit (10mW/cm squared).
Thanks all who contributed - I'll make sure I keep "13ft for the Honeywell RDR-4B on large Boeings and Airbus" away when its wx radar is on....