Met. Radar ON during Taxi
 

I saw it on a video, showing a flight deck of a 747-400 during taxi.
It was clearly seen on the video that the pilots had their met. radar turned on.
I am on C550 and this is my fifth type rating so far, and I was learned that turning it on while on ground (exept in "line up" position) can cause hazardous situation.
Eny one from ''Big Top'' could explain this instrument setting to me?

Highly appreciated!!

Littlejet

We have two types of Radar on our A/C, both are only switched on once cleared to line up.
We can test one type on stand the other you must again wait untill cleared to line up, this can present a problem if it is found to be U/S and we have to taxi back on to stand; so saying I've never yet had to do this as its pretty reliable anyway. :)

Putting to one side any specific radar unit requirements which may exist, the general problem is two-fold -

(a) reflective surfaces close in may cause damage within the radar unit

(b) if personnel are close to the radiating energy, they are at real risk of soft tissue damage - eyes for instance - a bit like a microwave oven.

Perhaps some of our rad techs/electrical engineers may like to comment ?

Radiated energy.
 

During the Vietnam conflict a US Air Force C-141 (or possibly a C-130) was taxiing in with its’ RADAR still turned on. The radiation painted a US Army Cobra, which was running up on the hardstand prior to take off. The radiated energy was so strong that it overcame the grounding on the missiles that they all fired and went down to the end of the field and exploded. The ammunition for the gun was electrically fired and all of it exploded in the ammo bay, which is just below the pilots. Needless to say they never knew what hilt them.

On a more personal note I was a techrep on the Atlas ICBM and was walking along side an Atlas, which was in the coffin complex lying down. The Air Force was conducting a RADAR check on the missile guidance system and the radiated energy caused two retrorockets to fire. They were several feet above my head and it was like standing next to two large gage shotguns going off next to my ears.

:cool:

Since AFAIK all Wx radars in common commercial use radiate when on TST, there is no excuse for turning the knob past "SBY" until lining up.

Can anyone else explain why doing otherwise might not be considered very poor airmanship?

Except for TEST modes, radar not on in terminal areas or on taxiways in proximity of traffic or buildings. And it's usually on STBY in flight in clear weather.

Well, all of that is true of the old technology radar, which emitted 50,000 watts. Those radars would tend to fry whatever happened to be too close. However, the new technology radars, Collins 2400 for example, only emit 25 watts and have a safety zone of only two feet required away from the antennea.

... my knowledge of matters dealing with electrons is miniscule .. but .... run that 50 kW tale past us all again ?

If you can wait a couple of days, I'll have my technical data that I will quote from. I hope it will help.

Most of the airborne weather radar sets that I have used (Bendix, RCA mostly) do not radiate in the test mode so can be tested at the gate accordingly.

Also, using the radar on the parallel taxiway approaching the runway is often quite useful as your departure procedure may indeed point you toward that direction. There is absolutely no problem with this procedure because the radiated power output from these sets is generally not dangerous beyond about twenty feet or so.

Have not flown military aircraft so cannot comment about the sets used in these machines.

One middle-east operator that I flew for required the wx radar to be on for takeoff because they believed that birds would be repelled by the radiated energy (even stating that the range should be selected to the lowest possible, for maximum results)...which is complete nonsense with the sets used in commercial aircraft.

The power of the pencil.
 

To: 411A

I passed this tidbit on to John T having forgotten to include it in my post above:

I used to work with an engineer that spent some time in the USAF as an electronics technician in England working on McDonnell F-4s. He told me that when they worked on the RADAR on the F-4 they would switch it over from wide beam to a pencil beam, which was highly concentrated. In this mode the RADAR could be steered and in doing so they would paint the buildings at the far end of the runway. The concentrated energy would play hell on the fluorescent tubes in the offices to the point that some would burst. No telling what it was doing to the personnel in the office as the material in the tubes is poison and then there is the radiated energy..

:eek:

Tex.............SHACK!

Today's new radars have 1/10 the energy of the old radars and won't do any harm.

I read recently (within the last 6 months) that FAA certification of high freq/lo emission radrs requires them to be safe beyond a distance of something like 95 cm from the radar head.

You could virtually straddle the nose of the aircraft without doing damage.

I will try and locate the reference and post it here.

That said, there is no need to turn the thing on in built up areas anyway.

Scanning your departure area is of great value as you taxi. This way one can decide if that ugly cloud is actually hazardous and if so, if it is too close to make a safe departure. This has been especially helpful at airports with no wx radar or airports with no wx reporting at all. Having said all this, use caution, don't use it near other aircraft, vehicles or buildings of any kind, and start with the tilt up.

This from the FAA in 1980
 

There is a newer version of this that i cannot find just now!!

The following information can be used in establishing a minimum safe distance from the antenna for personnel near an operating airborne weather radar. An applicable graph is shown in figure 1.

1. NEAR FIELD/FAR FIELD INTERSECTION. The distance to the near field/far field intersection can be computed by:


Ri = Gl/8p

where Ri - Intersection distance from the antenna (in meters)
l - Wave length (in meters)
G - Antenna gain


2. DISTANCE TO 10 mw/cm" SAFE LIMIT. For a far field power density of10 mw/cm", the distance (in meters) from the antenna may be calculated by:

Rs = Sq Rt GP/400p

where Rs - The minimum safe distance in meters.
P - Transmitted average power in watts.
G - Antenna gain



3. PROCEDURES. The above formulas or the graphs of figures 1 and figure 2. may be used to determine the minimum safe distance. In either case the following procedures apply:

a. Determine the distance (Ri) to the near field/far field intersection (paragraph 1).

b. Determine the distance (Rs) to 10 mw/cm" power density (paragraph 2).

c. If the distance (Rs) determined in 3b above is less than (Ri) found in 3a above, use distance (Ri) as the minimum safe distance.

d. If the distance (Rs) determined in 3b above is greater than (Ri) found in 3a above, use distance (Rs) as the minimum safe distance.

4. EXAMPLE

a. Data. The following is typical data for an airborne weather radar.


Antenna Diameter : 22 inches = 56 cm
Transmitter Frequency : 9375 : 30 MHz
Wave Length : 3.2 cm
Pulse Length : 1.5 microseconds (search)
Pulse Repetition : 400 Hz
Peak Power : 40 kilowatts
Average Power : 24 watts (search)
Antenna Gain : 1000 (30db)


b. Calculations.

(1) Distance (Ri) to the near field/far field intersection.


Ri = Gl/8p

= 1000 x 0.032/8p

= 1.27 meters = 4.2 feet


(2) Distance (Rs) to 10 mw/cm" safe limit.

Rs = Sq Root GP/400p
= Sq Root 1000 x 24/400p

= 4.37 meters = 14.3 feet


The distance (Rs) is greater than (Ri), therefore, the minimum safe distance is 14.3 feet.

If you have any questions on this PLEASE DON'T ASK ME!!!!!!!!!!!

Big Flaps, excellent ! but you really should get out more . :D

Further to 411A's post, does the Jepp plate for Venice still advise wx radar to be kept on to deter bird strikes?

down here in Africa we sometimes leave the radar on for t/o, for the purpose of scaring away the birdies...

question: what is the angle at which the radar on a C208 and F406 would indicate or scan on a level plane ahead? of course assuming that the a/c is flying stright and level.....it seems that about 5.5 to 6.5 degrees generates a scan like that

is this a function of the angle of incidence and the way the tx/rx is mounted ?

thanks