WX radar PAC alert

[Hardy Heinlin]

Good morning,

is there anybody on the forum who has flown with a radar that provides PAC alert (Path Attenuation Compensation alert)?

The alert is displayed as a yellow arc fragment on the outer arc of the ND compass rose. I know how it looks like on an expanded compass rose, but I'm unsure how it's displayed on the centered compass rose.

On the centered compass rose the radar image goes beyond the compass arc, i.e. a radar shadow may lie outside the compass arc. If the yellow PAC alert is placed directly on that centered compass arc, it may lie in front of a radar shadow and that looks bizarre in my tests.

In short words: Where is the yellow PAC alert displayed when the compass rose is centered?

Difficult question. I'm sure nobody knows it :-)


Cheers,

|-|ardy

[stekeller]

Hardy:

This may not help much, but it's from a recent 747-400 pilot (Tim Gleason, who you may remember from AV-ED at Leesburg)

"Good question.  You can see PAC alerts all the time, but I don't recall what it looked like in centered compass mode. No one really uses centered mode unless they are trying to see waypoints behind them to anticipate turns during SIDs and such."

- Stekeller
KORD

[Hardy Heinlin]

Thank you, Stefan.

Perhaps the alert is not displayed at all in centered mode.


Cheers,

|-|ardy

[delcom]

Very good question, Hardy.

I find no info on the PAC alert bar in centered mode, all illustrations I have show this feature in expanded mode only. If I have the chance, I'll try to trigger one (by full down tilt), then switch to centered...see what happens.

One thing for sure...no PAC alert bar in MAP mode.

EDIT: PAC is also disabled if the gain control is not in CAL and outside of the STC (Sensitivity Time Control). So beware of the gain even in WX or WX+T mode.

And of course the magic number for PAC alert is 80nm or less from the aircraft.

regards,
delcom

[Hardy Heinlin]

Thank you, Delcom.

Yes, those conditions (CAL, 80 nm etc.) are included in my model.

One thing for sure...no PAC alert bar in MAP mode.

You mean CTR mode? Edit: Now I got it, you mean WXR MAP, not ND MAP :-)

I'll try to trigger one (by full down tilt)

Interesting. Does this mean that whenever the radar horizon lies within the map (dark arc around the image) the PAC bar occurs?


Cheers,

|-|ardy

[Hardy Heinlin]

PAC alert on heading 125:





Some more radar shots ...

No clouds, just ground clutter, radar in manual mode.
Left: Tilt down. Right: Tilt up.




Clouds and ground clutter, radar has just been switched to AUTO.
Automatic removal of ground clutter, from sweep to sweep, in 16 seconds:





[size=8](click to enlarge)[/size]


Cheers,

|-|ardy

[delcom]

Yes, I meant WXR MAP mode. ;-)

BTW...ND modes. Of course you can display weather radar in all ND modes (CTR and EXP) except PLN mode.

***Interesting. Does this mean that whenever the radar horizon lies within the map (dark arc around the image) the PAC bar occurs?***

That's a good one, too. I have not thought about this earlier. However I doubt it. PAC logic seeks for radar shadows behind attenuated areas only. Just because the upper edge of the beam sweeps at 79nm (not intersecting the 80nm circle) it won't trigger a PAC bar...at least I don't think so.

Aiming down the antenna? That's how I'll try to get a PAC bar. I do not expect the storm of the century next month. There is a chance that there won't be a single cloud when I'll perform this little "test". Once we have our bird ready sitting in front of the hangar, I'll try to use the strong returns caused by terrain, buildings, etc to get radar shadow(s). Hopefully that will create PAC bar(s). I'm sure, Hardy...you are aware of multiple PAC bars displayed at the same time.

regards,
delcom

[delcom]

PAC alert on heading 125:

Nice screenshots, Hardy. Amazing job you're doing.

One little thing: PAC bars have very distinctive sharp edges, so it cannot be mistaken with actual return signals. The soft wavy alert bar of yours looks more like moisture returns. Does not alert me at all. Of course even the blind can see the huge shadow behind that storm.

Give 'em sharp edges and they'll be just fine.

EDIT: is PWS included in your WXR?

sincerely,
delcom

[Hardy Heinlin]

Multiple PAC bars, yes.

Sharper bar? In fact, that would've been my next question. Is the bar generated in the radar imaging box and sent through the radar bus -- or is it generated in the EIU/IDS symbol generator?

In other words, is the PAC bar brightness controlled by the inner or by the outer brightness knob?

If it's on the radar bus, I cannot get rid of the fuzzy look (just like the EGPWS terrain database number on the terrain test image cannot get sharper on the real ship).

PWS is on the todo list.


Cheers,

|-|ardy

[John H Watson]

Precisely.

How non-wavy are the PAC lines?

These Predictive Windshear lines are somewhat wavy in closeup, but fairly straight from a distance.



JHW

[Zinger]

a. The name of this Multiscan Radar capability is Path attenuation compensation.
b. Little hard evidence, with some speculation:
1. The mode is useful for high altitude flight in which two beams collect return from the reflective cloud portion and above it in the non-reflective, cloud top and above cloud. That way CAT is detected. In such flight phase, MAP is the main ND mode.
2. Such detection, analysis and display is performed by the radar relative to the aircraft and radar reference axis. See picture below. That is very close to the ND reference axis in all modes (except PLN which has no radar imagery display).
3. So my guess is that it is as shown in the Collins picture, superimposed on ND, and indicating if any rerouting is required to avoid the unsafe zone.
The picture could also assist regarding the shape of the yellow segment stripes.

[picture]

Edit: Just noticed somewhat of a copyright infringement, please remove the picture if necessary to correct it. Sorry.


Edit (HH): The picture is on page 14 in this PDF:
http://www.rockwellcollins.com/content/pdf/pdf_3344.pdf

[delcom]

Was this google translator? I did not understand a thing.

EDIT: Or is it just me?

all due respect,
delcom

[Hardy Heinlin]

Thanks, Zinger.

All info is already available in those Collins brochures and user manuals. The main question remaining is:

Is the yellow PAC bar ...

a) drawn in the radar imaging box and then sent through the radar raster bus to the EIUs? (Fuzzy look and inner brightness knob has control.)

b) Or is it generated in the EIUs? (Sharp look and outer brightness knob has control.)


Regards,

|-|ardy


Edit: The other remaining question is: Is the PAC alert bar also shown when the ND compass rose is centered (not expanded)?

[Hardy Heinlin]

Using the left and right NDs for comparison: Captain's INBD CRT brightness control for raster brightness (inner knob) at max, and that of the F/O very low:  



If the PAC alert bar is on the radar raster bus, the alert bar won't be visible when the pilot has turned the raster brightness (inner knob) down.

This is just an Alpha version. I don't know where the PAC bar is generated -- is it done in the raster image generator or in the IDS symbol generator?


|-|


[size=8]Edit: Just to avoid confusions in advance: This round MAP knob is not for the ND MAP mode, and not for the WX MAP mode :-)[/size]

[John H Watson]

Surely it would have to be a raster-generated image. Just think of the complexity of sending information regarding multiple pac segments at different angles via Radar to the EIU's.
Also, as far as I can see, there are no databuses going from the Weather Radar System to the EIU's (only discretes).

a) drawn in the radar imaging box and then sent through the radar raster bus to the EIUs? (Fuzzy look and inner brightness knob has control.)

The raster information goes directly to the IDUs, not via the EIUs. This is the same for Terrain displays.

If I have the chance, I'll try to trigger one (by full down tilt),

From an engineering manual:

"This feature is only seen by the flight crew, but it is important that
the ground engineer is aware of its existence."

This almost suggests an air/ground input!

Regards
JHW

[delcom]

John,
as far as I recall it...air/ground logic of WXR is for PWS function and MAP mode enable/inhibit only. I'm planning to shoot weather(WX, WX+T), not terrain (MAP).

regards,
delcom

[delcom]

[size=8]Edit: Just to avoid confusions in advance: This round MAP knob is not for the ND MAP mode, and not for the WX MAP mode :-)[/size]

Lol,
delcom

[Hardy Heinlin]

Speaking of "Predictive Windshear lines": With the ND compass centered these lines will probably look strange also. (Just a side thought, I'm not working on that. That problem is certainly worth a new thread.)

|-|ardy


Quiz: Find Lake Geneva in this thread

[John H Watson]

That problem is certainly worth a new thread.)

|-|

Since the Weather Radar self test produces the PWS pattern, I imagine it would be very simple to get a shot of this in centered mode. Perhaps it will also give us answers to the centred PAC display, since both involve yellow lines

Rgds.
JHW

[Jeroen Hoppenbrouwers]

The raster information goes directly to the IDUs, not via the EIUs. This is the same for Terrain displays.

So... if we depower the EIU, but not the radar and not the terrain generator (EGPWS?) and not the IDU... do the raster images remain on display?


Jeroen