A320 overheating avionics symptoms

[Dupre]

Hi, I had a failure of the avionics ventilation system on the ground in an early (<1000 MSN) A321. After a few minutes the PFD and ND lost some of their colour, most notably the grey background turned black behind the speed, altitude and heading tapes. It was pretty obvious something was amiss, but took me a minute to put my finger on what was different.

Is this by design of airbus, or is it just a lucky coincidence that hot avionics give you this warning?

Also, someone told me once that with hot avionics, the first thing to go is the wx radar image, Sure enough I turned the radar and no image showed, nor did the tilt. Why would this be?

Thanks!

[ACMS]

Turned on the radar on the ground, I hope you weren't parked......:eek:

[Dupre]

The whole thing happened on the taxi out, tested the radar at the holding point before returning to gate.

[STBYRUD]

Quote from FCOM DSC-31-40 P 1/70
Note: A grey background appears on the speed, the heading vertical speed, and the altitude
speed scales of the PFD . If the Primary Flight Display (PFD ) Unit temperature exceeds a
defined threshold, the grey background disappears, in order to limit power consumption and
prevent a DU overheat. Any additional increase in temperature will lead to a complete cut
off of the power supply to this display unit.
and FCOM DSC-31-45 P 1/88
Note: In case avionics ventilation is not sufficient (e.g. due to a blower and extract fan failure),
and the Navigation Display (ND ) Unit temperature exceeds a defined threshold, the ND will
not display the weather radar image, in order to limit power consumption and prevent a DU
overheat. Any additional increase in temperature will lead to a complete cut off of the power
supply to this display unit.

That should only apply to older ships with CRT displays.

[Dupre]

Wow thanks!
Slightly embarrassing that I haven't read that before (or at least haven't remembered it...)
But answers my question fully!

[Fursty Ferret]

Turned on the radar on the ground, I hope you weren't parked......:eek:

Unless someone has their hand in the mechanism when it's turned on, the "nuked by weather radar" thing is a myth.

[ACMS]

Go ahead then, you can stand in front of my radar any day.

[Fursty Ferret]

Fine by me.

[Flo121142]

Not to be too off topic, but did not want to start a new thread for this...how would the removal of the WX radar picture due to overheating manifest itself? Would only the picture disappear or also the "Tilt" Information in the corner of the ND? I'm just wondering as I had a weird intermittent radar failure during a line check recently. We were trying to avoid some pretty big CBs over Bulgaria in a middle aged A320 (LCD Displays, MSN around 2500) when suddenly and without any other indication (so rather subtle) the WX Radar picture and the tilt setting disappeared from both NDs (our first thought was that we inadvertently switched it off, but when we checked it was still in the on position). We recycled the switch by briefly setting it to the Number 2 position and then back to the Number 1 position (only one radar on this airplane), this action had no effect. We then put Terrain on ND on the Captains side. After he removed the Terrain the radar started working again (the whole time from recognition of the condition until it started working again was around 3 to 4 minutes). No idea if the recycling of the Terrain switch helped sorting it out or if it was just coincidence. We checked the CFDS In Flight Report as well afterwards, it didn't record any failure. Is it possible that the cause was a temporary overheating of the avionics?

[FlightDetent]

Flo: I am under the impression that the removal of WX picture is limited to CRTs, in the sense discussed above.

Yours story sound like a gremlin at large.

[Dupre]

yes, have a look in the reference STBYRUD kindly posted in your fcom.

In my fleet it only mentions the overheating and radar image on CRT models, not ones with LCD displays.

But as an aside, when i was checking the wx radar with overheating avionics, I also noticed that the tilt display on the ND had also disappeared.