Dangerous Radar Altimeter waves?

[AirJockey]

A few years back I was told to avoid walking under, or staying under the tailboom for a prolonged period of time on a running helicopter because the radio waves the Radar Altimeter produced could be dangerous to your "private parts". Is there any truth to that, and if so, many people in the offshore industry is, has, will be exposed to the radio waves many times a day when they work as heliguards. The radio waves are after all quite powerfull, but I thought they stopped transmitting as soon as you landed?

We are having a discussion at work about it and I would very much appreciate any inputs you might have on the issue.:confused:

[Avnx EO]

I don't think you have to worry about it too much....

The typical rad alt puts out a few hundred milliwatts RF power at about 4GHz (milliwatt = thousandths of a watt) . Most rad alt installations I've dealt with are not tied to the squat switch and continue to radiate while on the ground. In fact most systems will radiate as soon as aircraft power is applied. The common RF sources you want to stay away from are weather radar (typically 10 or more kilowatts at a few GHz), and HF antennas (typically several hundred watts at 2-30 MHz) Weather radars will cook your brain (with 10-20 feet or so), and HF will actually burn you if you are close enough.

The standard danger from RF is heating of your inards by RF energy (like a microwave oven). The amount your body absorbs depends on frequency and power. At microwave frequencies it takes less power to get you toasty. The shorter waves (higher frequencies) tend to be absorbed, while the longer waves (lower frequencies) pass through you.

Distance is also a big factor. Typically there's the "R-squared" law to consider - that RF power tends to decrease proportional to the sqaure of the distance from the antenna. But that's for Omni antennas, a beam antenna, like that used for rad alt will keep the power pointed in one direction (like the 60 watt headlight in your car keeps the light focussed in one direction as opposed to a naked light bulb) In either case, the intensity drops with distance - but faster for the naked bulb than the headlight.

Put it into perspective.... Your 2.4 GHz cordless phone held within an inch of your head probably gives you a worse RF exposure than you get from your rad alt at a foot or so. Also consider most aircraft com radios put out 5 to 15 watts (depending on model) but in the 108-136 MHz.

Me, I'm not worried about rad alts, but I do try and limit my exposure to RF sources in general. There's the famous story about highway patrol cops getting a higher rate of testicular cancer. Turns out that when going from one speed trap location to another, they were laying their radar guns in their lap (zero distance - maximum power.) And those things (especially the older models) put out more than most rad alts. But even there the key is power and prolonged exposure (like sunburns and skin cancer)

So unless you are taking prolonged naps under the tail boom with your "private part" right up against the antenna, and with ships power applied, I wouldn't worry about it.

[AirJockey]

Thanks Avnx EO. A lot of interesting stuff which you normally wouldn`t find in any aviation books. It is actually an issue of interest espesially for EMS operators and Offshore workers.

Wx Radars are off course quite dangerous to step in front of unless it is off.

Lost a six pac on this one, but learned something new, again......