Over and between the weather / From Sabadell LELL to Friedrichshafen EDNY

Peter wrote:

I think the difference between on-board radar and the ground based weather radar is the vertical beam width.

The big difference is that aircraft is looking from above while ground based radar is looking from below. When using an on-board radar, you have to deal with ground clutter which will conceal low level precipitation (you’re essentially looking against a very noisy background while ground based radar has a very nice background in comparison). They have much smaller antennas (hence broader beam) and I assume are less powerful.

The former has an adjustable tilt so the vertical extent of the wx can be estimated, whereas the latter is a fixed beam.

I was never taught to estimate vertical extent (with the intent of determining whether I could fly over it). The core is most reflective and those lie at about 12 +-4 thousand feet. You want to point your radar there. You then look for shadows cast by cores. Ground clutter can give you strong returns, but it won’t cause shadows (and by ground clutter I mean cities, not mountains – those do cast shadows). If you identify a strong core, you shouldn’t be flying over it. You should stay away. At that point, it really doesn’t matter how high it goes. Perhaps if I could get to 50 thousand feet.

Ground based radar should also be aimed for the cores to give calibrated representation AFAIK. That band is fixed. Red means a lot of precipitation so unless I can visually verify the state, I don’t want to be there. At any altitude.

denopa wrote:

it’s very different if you have nose radar that’s 20 degrees wide and powerful enough to paint stuff out to 80nm, or if your radar is in your wing, 10 degrees wide and good out to 30nm.

Without being picky that is the wrong way around. The larger the antenna, the narrower the beam which is why it is effective to a greater range. So the 10" antenna on the PA46 has a beam width of 10 degrees whereas the 12" on the Mustang has a beam width of 8 degrees.

More can be read on the excellent website. http://code7700.com/radar_tilt.html

Image below from that site.

@Peter – the onboard wx-radar does not show pure ice crystals (matter of wave length). So the idea behind the antenna tilt is to find the section of the CB with the big water droplets in it and to avoid it laterally. Never try to set the tilt to 0° in IMC thinking you would avoid the cloud if nothing appears on the scope – the antenna tilt accuracy is +/- 5°
acc. to the radar manufacturer (of the aircraft types I flew). Additionally researchers found CBs popping up at rates of more than 5000ft/min.
The advantage of ground based wx radar is that almost no attenuation effect occurs, i.e. you have a truer picture of the situation whereas the onboard radar theoretically can hide an echo that is behind a strong one in the foreground.

Peter,
you are correct about on-board. If used properly, it tells you what’s in front of you now; in front meaning within a cone that extends left, right, up and down to some extent. With tilt you can adjust to see only what’s below your current altitude, or above it, which means you can know what’s at your altitude. Having said that it’s no so easy to use; first of all you don’t get that many occasions to use it (at least I don’t), secondly a lot of the training that’s available isn’t installation specific and it needs to be: it’s very different if you have nose radar that’s 20 degrees wide and powerful enough to paint stuff out to 80nm, or if your radar is in your wing, 10 degrees wide and good out to 30nm.

Had a similar experience yesterday flying from EHRD to ESSB. Without some kind of wx in the cockpit, even if slightly delayed, it’s practically impossible to fly in these conditions.
Dutch and German ATC as efficient and helpful as always.
Safe flying.

ps. very friendly and easy handling at ESSB fyi.

I don’t know much about this (I would not fly in those conditions in IMC in the plane I have) but I think the difference between on-board radar and the ground based weather radar is the vertical beam width. The former has an adjustable tilt so the vertical extent of the wx can be estimated, whereas the latter is a fixed beam.

Peter wrote:

At best, it will give you an overly cautious impression (which is good) because you can have really dense radar regions but the tops might be FL100-150.

I thought the rule of thumb was that if it’s red, it’s high and you shouldn’t even think about flying over it in a SEP. At least without an on-board radar. You shouldn’t get that heavy precipitation otherwise. Of course, even ground based radar can catch some clutter. Anyway, IR coverage the ADL offers is better than radar coverage and strike coverage is good too, so you can correlate it.

denopa wrote:

When using onboard radar, the advice is to avoid the green parts as well, as long as they belong to stuff with yellow or more in them. I actually don’t know what the guidance would be for downlink radar. I have had flight where I was in the green parts of the DL and the onboard radar was showing absolutely nothing.

I was told to stay at least 20 NM away from a core (horizontally). Green on an image from a ground based radar can easily be a low level stratus slowly raining, nothing that would concern you in cruise (unless your machine has low service ceiling). It will blend with ground clutter on an image from an on-board radar.

I too have used the O2D2 with the “mask” setting, to get 95%+ at FL200. It works really well. I’ve done it with passengers too so it isn’t just me.

Regarding radar, I don’t think uplink radar (basically, meteox.com) is good for wx penetration in IMC unless you have separately established the probable total absence of CBs. At best, it will give you an overly cautious impression (which is good) because you can have really dense radar regions but the tops might be FL100-150.

Thanks, Chris. I achieved merely 90% @ FL200 with the D10-setting. Next time I’ll also switch to the F-mode.