CB tops and manual Gain radar technique may prevent unpleasant surprises
Thread Starter
CB tops and manual Gain radar technique may prevent unpleasant surprises
QF severe turbulence encounter last year.
AO-2009-029
Hit a CB top at night. There was no mention in the report of gain control use by the crew. Useful hint from radar manuals is to use manual gain control at max setting at high altitudes. This produces more radar power (3000 percent is the figure quoted) and CB tops of ice crystals can often be detected as a slight echo. However if gain control is in auto mode the tops may not show up at high altitudes. Once the very small echo of the ice crystals in the CB are seen on the radar screen (usually at 40-60 miles depending on tilt), the actual extent of the CB is readily seen by lowering the tilt with gain in auto. Good way to prove the theory is to practice this technique in the clear on isolated CB's. In one Pacific airline I flew with on 737's this technique worked well and saved us grief at night or IMC.
AO-2009-029
Hit a CB top at night. There was no mention in the report of gain control use by the crew. Useful hint from radar manuals is to use manual gain control at max setting at high altitudes. This produces more radar power (3000 percent is the figure quoted) and CB tops of ice crystals can often be detected as a slight echo. However if gain control is in auto mode the tops may not show up at high altitudes. Once the very small echo of the ice crystals in the CB are seen on the radar screen (usually at 40-60 miles depending on tilt), the actual extent of the CB is readily seen by lowering the tilt with gain in auto. Good way to prove the theory is to practice this technique in the clear on isolated CB's. In one Pacific airline I flew with on 737's this technique worked well and saved us grief at night or IMC.
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You may have heard the term: Antenna Gain
This term is somewhat misleading. It sounds as though the microwave energy enters the antenna and is somehow increased before leaving it.
That interpretation of Antenna Gain are incorrect!
The term Antenna Gain describes how much the energy leaving the antenna is focused into a particular direction.
This term is somewhat misleading. It sounds as though the microwave energy enters the antenna and is somehow increased before leaving it.
That interpretation of Antenna Gain are incorrect!
The term Antenna Gain describes how much the energy leaving the antenna is focused into a particular direction.
Thread Starter
The term Antenna Gain describes how much the energy leaving the antenna is focused into a particular direction.
"The ability to adjust the gain control during weather detection modes provides some advantages in weather detection at the shorter ranges. Specifically, aircraft operating at high altitudes run a greater risk of encountering low reflectivity targets such as ice crystals. Adjusting the gain to provide maximum detection will aid in locating areas of low reflectivity targets.
By increasing the system gain, the pilot can effectively broaden the beam width of the transmitted signal (within the first 50 nm) to produce returns from targets that might have been otherwsie over-scanned. Once again, judicious use of the tilt and gain controls to discover the extent of nearby targets is recommended".
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I would say from my experience that 95% of QF crews use MAX nearly all the time above 20000'. CAL is recommended below during terminal manoeuvring.
...but max can be pretty useless at times with ice crystals and some build ups no matter how much you scan below (or above).
...but max can be pretty useless at times with ice crystals and some build ups no matter how much you scan below (or above).
I would like to add that max gain should be used in conjuction with some tilt manipulation to give a pilot best understanding of the weather ahead.
In the early 90's, The A330 radar is so useless that what should be red showed up as scatted greed dots. So, we have to repeatedly tilt it down to minus 8 the move it up a notch every sweep. Using simple 1-in-60 rules, we learn to read the cloud and manage to make a smarter guess of where is the top of the nasty bit where anything on top of that should be ice crystals. That help to decide how much to avoid or what can go through. Those monsters sitting over Indonesian airspace gave many good practices.
Used the same method in the B737 and B777. Works even better as these radars are more accurate.
In the early 90's, The A330 radar is so useless that what should be red showed up as scatted greed dots. So, we have to repeatedly tilt it down to minus 8 the move it up a notch every sweep. Using simple 1-in-60 rules, we learn to read the cloud and manage to make a smarter guess of where is the top of the nasty bit where anything on top of that should be ice crystals. That help to decide how much to avoid or what can go through. Those monsters sitting over Indonesian airspace gave many good practices.
Used the same method in the B737 and B777. Works even better as these radars are more accurate.
Thread Starter
Centaurus, why assume the radar wasn't in MAX already?
Last edited by Centaurus; 3rd Jul 2010 at 08:24.
Centaurus
I Know your background and acknowledge your wide experience. I would however suggest that your advice in this area is not appropriate to some more modern radar units.
I Know your background and acknowledge your wide experience. I would however suggest that your advice in this area is not appropriate to some more modern radar units.
The CAL (calibrated) gain setting yields the most accurate correlation
CAL gain is the recommended gain position for normal operation.
Figure 4-38 shows a radar display with gain set to CAL.
of color levels (black, green, yellow and red) with actual rainfall rates
and their corresponding thunderstorm threat levels.
CAL gain is the recommended gain position for normal operation.
Figure 4-38 shows a radar display with gain set to CAL.
The above exerpt is from the Collins WXR2100 manual.
I can't tell you how frustrated I get sitting next to guys who, lacking an understanding of advances in the radar world, apply procedures that are outdated and inappropriate to the equipment they are using, and end up diverting around returns that are either innocuous or below them.
Proffer advice by all means, but may I suggest you qualify it.
Maui
Last edited by maui; 3rd Jul 2010 at 09:15.
I hardly ever use man gain on the 330, 777, 737 or 744. We were taught from day 1 what maui said above and I agree with him.
That's not to say I don't switch to man every now and then when the situation warrants further investigation. Including using low gain in high rainfall areas whilst down low in the Terminal area.
Constant use of tilt and range is a must.
I very rarely see the FO or SO with 320 nm range and 1 down tilt on a dark night over the Pacific anymore, but I used to.
That's not to say I don't switch to man every now and then when the situation warrants further investigation. Including using low gain in high rainfall areas whilst down low in the Terminal area.
Constant use of tilt and range is a must.
I very rarely see the FO or SO with 320 nm range and 1 down tilt on a dark night over the Pacific anymore, but I used to.
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I carried a couple of technical types from one of the radar manufacturers a couple of years ago. They were investigating that with the radar in auto, why CBs did not show up that well whilst flying over the Pacific. They came to the conclusion that the radars were calibrated for North American CBs which are apparently wetter.
Perhaps I'm just a luddite because I still use manual with the appropriate tilt/gain for the selected range................ it works well for me!
Perhaps I'm just a luddite because I still use manual with the appropriate tilt/gain for the selected range................ it works well for me!
Thread Starter
I would however suggest that your advice in this area is not appropriate to some more modern radar units.
offchocks.
The same happened with the new modern ( sic ) radar on the 777-300ER that was introduced by SQ in 2007. The Honeywell RDR4000 had to be re-calibrated to suit the rest of the world conditions after they discovered it couldn't see shi* outside N.A.
And after 2 years using it I was not really that impressed........Give me a tilt any day thanks.
They came to the conclusion that the radars were calibrated for North American CBs which are apparently wetter.
And after 2 years using it I was not really that impressed........Give me a tilt any day thanks.
The Collins Manual is here.
The first part of the manual is specific to the 2100 radar itself.
The rest is about weather radar and weather in general, and operating tips.
The first part of the manual is specific to the 2100 radar itself.
The rest is about weather radar and weather in general, and operating tips.